EPA-600/2-76-097
April 1976
Environmental Protection Technology Series
FEASIBILITY OF A HEAT AND
EMISSION LOSS PREVENTION SYSTEM FOR
AREA SOURCE FURNACES
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects "Research
2. . • Environmental Protection Technology
.3.. Ecological Research
4." Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield. Virginia 22161.
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EPA-600/2-76-097
April 1976
FEASIBILITY OF A
HEAT AND EMISSION LOSS PREVENTION SYSTEM
FOR AREA SOURCE FURNACES
by
R.A. Brown, C.B. Moyer, andR.J. Schreiber
Aerotherm Acurex Corporation
485 Clyde Avenue
Mountain View, California 94042
Contract No. 68-02-1318, Task 5
ROAPNo. 21ADD-042
Program Element No. 1AB013
EPA Task Officer: W. B. Steen
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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FOREWORD
This report presents the results of a study to determine the feasibility
of candidate concepts for simultaneous heat and air pollutant emission recovery
from the combustion products of domestic-size furnaces. The study was performed
by the Aerotherm Division of Acurex Corporation for the U.S. Environmental Pro-
tection Agency.
Aerotherm extends its appreciation to Mr. Kenneth M. Brown for his val-
uable assistance with the detailed heat transfer analysis.
The EPA Task Officers were Mr. D. B. Henschel and Mr. W. B. Steen. The
Aerotherm Program Manager was Dr. Larry W. Anderson. The study was performed
during the months of June through September 1974.
iii
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TABLE OF CONTENTS
Section
1 SUMMARY 1
2 INTRODUCTION 6
3 DEFINITION OF PROBLEM AND EXISTING TECHNOLOGY 8
3.1 Energy Consumption and Methods of Energy Savings 8
3.2 Furnace Types 21
3.3 Furnace Design Practice 27
3.3.1 Central Air Gas Fired 27
3.3.2 Central Air-Oil Fired 31
3.3.3 Hot Water-Gas Fired 34
3.3.4 Hot Water-Oil Fired 34
3.3.5 Furnace Efficiencies and Standards 39
3.4 High Efficiency Furnace and Heat Recovery Device
Research 47
3.5 Heat Recovery Devices Commercially Available 64
3.5.1 Isothermics Air-0-Space Heater 64
3.5.2 Dolin Metal Products - Heat Reclaimer 66
3.5.3 Other Manufacturers and Devices 66
4 IDENTIFICATION OF ALTERNATE HEAT RECOVERY DESIGNS 71
4.1 Retrofit Schemes 71
4.1.1 Black Box Approach 71
4.1.1.1 General Discussion 71
4.1.1.2 Design Problem Areas 75
4.1.1.3 Conclusions 80
4.1.2 Internal Modifications 80
4.2 New Furnace Designs 82
4.2.1 Increased Heat Transfer Surface 82
4.2.2 Novel Approaches 82
4.2.2.1 Catalytic Combustion 83
4.2.2.2 Submerged Combustion 85
4.2.2.3 Thermoelectric Device 85
4.2.2.4 Other Concepts 88
5 DETAILED ANALYSIS OF RETROFIT SCHEMES 89
5.1 Schemes 3A and 4A
5.2 Scheme 4W 104
6 SYSTEM COST 109
6.1 Potential Saving and Payback Period 109
6.2 Cost of Retrofit Units 114
6.3 New Furnace Designs 115
6.4 Cost of Conventional Designs 117
6.5 Conclusions 120
v
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TABLE OF CONTENTS (Concluded)
Section Page
7 CONTROL OF AIR POLLUTANT EMISSIONS FROM RESIDENTIAL HEATING
EQUIPMENT 121
7.1 Introduction 121
7.2 Control Strategies for Emissions From Residential
Heating Systems 123
7.2.1 Combustion Process Modification 123
7.2.2 Post-Combustion Control 125
7.3 Principal Recent or Current Residential Emission
Reduction R&D Efforts 125
7.4 Conclusions 125
8 POTENTIAL MARKET 129
8.1 Potential Market Estimate 130
8.2 National Reduction in Fuel Consumption 130
9 CONCLUSIONS AND RECOMMENDATIONS 138
9.1 Conclusions 138
9.2 Recommendations 139
REFERENCES 141
APPENDIX A A-l
VI
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LIST OF FIGURES
Figure Page
1 Heating Equipment, by Regions: 1970-Percent (All Occupied
Units) 23
2 House Heating Fuel, by Regions: 1970 Percent (All Occupied
Units) 24
3 Gas Fired-Forced Air Furnaces (Courtesy Sears Roebuck
& Co.) 29
4 Gas Fired Forced Air Downflow Furnace and Details of Com-
ponents (Courtesy Coleman Co. and Westinghouse) 30
5 Oil Fired Central Air Furnace (Courtesy Day & Night Co.) 32
6 Typical Oil Burners (Courtesy Johnson Oil Burner Co.) 33
7 Gas Fired Hydronic Boiler (courtesy of the Raypack Co.) 36
8 Oil Fired-Hydronic System (Courtesy of Weil-McLain Co.) 38
9 Temperature Rise Across Oil Furnace During a Typical
Normal Cycle 43
10 Temperature Rise Across Gas Furnace During a Typical
Normal Cycle 44
11 Energy Balance for a Particular Cycle of Oil Furnace (Top)
and of Gas Furnace (Bottom) 45
12a AMANA Electric/Gas Heating Cooling Unit Using the HTM* 48
12b AMANA Heat Transfer Module 49
13a The High-Velocity, High-Temperature, Forced-Air Baseboard
Heater System 51
13b Section View of the Heat Exchanger and Air Flow 51
14a Cross Section of Ceramic Heat Exchanger-Burner Unit 53
14b Cross Section of Ceramic Heat Exchanger Force-Air Furnace 54
15 Schematic Illustration of the Pulse Combustion Process 55
16 An Experimental "Finned Tube" Pulse Combustion Furnace 56
17 An Experimental, Lo-Boy Pulse Combustion Furnace 57
18 An Experimental, Hi-Boy Pulse Combustion Furnace 58
vii
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LIST OF FIGURES (Continued)
Figure Page
19 An Experimental, Warm Air Heating Panel System 59
20 An Experimental Heat Exchanger for a Warm Water Heating
Panel Application 60
21 Experimental Direct-Fired Wall Panel 61
22 Experimental Snorkel-Vented Dual Wall Furnace with
Bypass Arrangement 62
23 Forced-Air Furnace with Integral Blower-Heat Exchanger 63
24 Isothermics - Air-0-Space Heater 65
25 Dolin-Heat Reclaimer 67
26 Dolin Heat Reclaimer Performance 68
27 Theoretical Dew Points of the Combustion Products of
Industrial Fuels 78
28 Potential Heat Recovery 81
29 Burner Arrangement - Submerged Combustion 87
30 Compact Heat Exchanger Designs 92
31 Typical Blower Performance Curve 94
32 Plate-Fin Heat Exchanger 98
33 Fin Tube Design 99
34 Performance of the Noncondensing Plate Fin Flue Gas to
Air Heat Exchanger 1000
35 Performance of the Noncondensing Fin-Tube Flue Gas to
Air Heat Exchanger 101
36 Performance of the Condensing Plate Fin Flue Gas to Air
Heat Exchanger 102
37 Performance of the Condensing Fin-Tube Flue Gas to Air
Heat Exchanger 103
38 Noncondensing Flue Gas to Water Fin Tube Heat Exchanger
(Scheme 4W-N) 105
39 Condensing - Flue Gas to Water Fin Tube Heat Exchanger
(Scheme 4W-C) 106
40 Potential Saving as a Function of Flue Temperature for
Retrofit Heat Recovery Device 111
Vlll
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LIST OF FIGURES (Concluded)
Figure Page
41 Payback Period as a Function of Heat Saved and Initial
Investment 113
42 Initial Investment Increment vs. Lifetime or Payout Period 118
43 Residential Fuel Saving Per Year 134
44 Savings Per Year 135
45 Oil Saving Per Year 136
IX
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LIST OF TABLES
Table Page
1 Energy Consumption in the U.S. by End Use 1968
(Trillions of Btu and Percent per Year) 9
2 Studies in Conservation of Energy from Residential and
Commercial Building 10
3 Savings from Modification of Characteristic Design
18
4 Breakdown of Energy Savings for Furnace Recovery and
Flue Damper 19
5 Residential Heating System in the U.S. 1970 Census 22
6 Furnace Systems Sold (GAMA) 25
7 Year Structure Built for Owner and Renter Occupied Housing
Units by Heating Equipment 1970 26
8 Typical Operating Conditions 28
9 Oil Fired Central Air Systems 35
10 Oil and Gas Fired-Hot Water Typical Operating Conditions
of Design Practice 100,000 Btu/Hr Input 37
11 Listing of Standards for HVAC Equipment which Include
Efficiency 40
12 Thermal and Service Efficiencies of Residential Hot Water
Boilers (Boiler A Differs from Most Contemporary Oil-Fired
Equipment 42
13 Heat Recovery Device Manufacturers 69
14 "Black Box" Heat Exchanger Schemes 73
15 Improvements to Existing Devices 76
16 Potential Materials of Construction 79
17 Aspects of Catalytic or Surface Combustion for Central Units 84
18 Submerged Combustion 86
19 Potential Schemes to be Analyzed 90
20 Heat Exchanger Performance Program (PERF) 93
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LIST OF TABLES (Concluded)
Table Page
21 Plate Fin Heat Exchangers - Flue Gas to Air 96
22 Fin Tube Heat Exchanger - Flue Gas to Air 97
23 Induced Draft Fan Requirements 104
24 Fin Tube Heat Exchanger - Flue Gas to Water 107
25 Fuel Cost $/Therm 110
26 Heat Exchanger Costs 114
27 System Costs and Payback Period 116
28 Annual Savings to Homeowner Using a Heat Pump Vs. Equivalent
Comfort-Conditioning Systems 119
29 Emissions From Natural Gas- and Oil-Fired Burners 122
30 Combustion Control Strategies for Reducing Air Pollutants
From Residential Heating Equipment 124
31 Post Combustion Control (Flue Gas Treatment) Strategies for
Air Pollutants From Residential Heating Equipment 126
32 Principal Recent or Current Residential Emission Reduction
R&D Efforts . 127
33 Estimate of Hot Water and Central Air Furnace Installation
for 1974 by Region (Millions) 131
34 Retrofit Schedule 132
35 Energy Savings 137
XI
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SECTION 1
SUMMARY
Residential space heating represents 11.0 percent of the total U.S.
energy consumption. Thus there is a strong incentive to reduce energy con-
sumption in the residential section particularly for space heating. There are
a great number of studies being conducted through the National Bureau of Stan-
dards, NSF, American Society of Heating, Refrigerating and Air Conditioning
Engineers (ASHRAE), American Gas Association, public utilities and others on
the overall problem of energy use reduction in residential heating and cooling.
These studies have shown that between 9 and 28 percent of the heating load
could be recovered by heat recovery of the furnace flue and shut off of the
flue during nonuse periods. This represents from 3.6 to 11 percent of the to-
tal energy consumption of the house and from 1 to 3 percent of total U.S. en-
ergy consumption. Other significant energy conservation techniques include
reduction of air infiltration and increased insulation in wall ceilings and
floors. However, none of these studies dealt directly with the development of
a heat recovery device.
The first step to develop a heat and emissions recovery system (HELPS)
is to determine the distribution of heating systems across the U.S., their ef-
ficiency, their design and limitations on their design. U.S. census data for
1970 show that the central forced air, gas-fired furnace is the principle heat-
ing method with oil and gas-fired hot water system and oil-fired central air
systems ranking 2, 5, and 4, respectively. In the Northeast section of the
country, oil-fired hot water systems are the most prevalent. However, in the
last ten years, gas-fired central air furnaces accounted for 29 to 46 percent
of the heating systems sold nationwide.
The gas-fired central air furnace typically has a steady state efficiency
of about 80 percent with oil-fired units either a few percentage points below
or nearly equal to the 80 percent figure. The gas-fired system uses an aspir-
ated burner and relies on the draft created by the buoyancy forces in the flue
to draw sufficient combustion and excess air through the furnace. This results
in very low pressures (.05" W.C.) in the combustion chamber, low heat transfer
coefficients and a low pressure drop through the unit. Higher efficiencies
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could be achieved with lower flue gas temperatures. At 80 percent efficiency,
the temperature of the flue gas exiting the furnace is such that condensation
is avoided in the stack and sufficient buoyancy is created to discharge the
flue from the stack.
Concepts for higher efficiency furnaces can be retrofit systems or sys-
tems applicable only to new installations. Retrofit concepts are important be-
cause of the large number of existing units that require attention. Concepts
that can be applied only to new installations deserve attention because they
offer greater potential in fuel, emission, and cost savings. Research aimed
at investigating both new and retrofit systems is ongoing.
Research on higher efficiency furnaces is being conducted by the furnace
manufacturers, oil companies and by the American Gas Association (AGA). The
Amana Company recently announced a new furnace design concept (Heat Transfer
Module) which utilizes a forced air surface combustion burner which transfers
heat to an intermediary fluid. Slightly higher efficiencies are claimed (5-8
percent) while flue gas temperatures are maintained high enough to avoid con-
densation.
AGA over the last 20 years has explored a number of unconventional con-
cepts for new installations. The most significant and one on which they are
still working is the submerged pulsed combustion concept. Efficiencies as high
as 95 percent are claimed for this concept which relies on condensation of the
water in the flue.
Two commercially available flue heat recovery devices have been identi-
fied for retrofit on residential heating systems. A heat pipe device manufac-
tured by Isothermics, Inc., of New Jersey can recover from 5,000 to 12,500
Btu/hr or 5 to 12-1/2 percent of a typical 100,000 Btu/hr furnace, depending
on flue gas temperature. A flue gas-to-air tubular exchanger is available from
the Dolin Manufacturing Company. Their unit recovers only from 3000 to 5300
Btu/hr. Other retrofit devices consist of off-cycle flue dampers to prevent
heat loss through the flue pipe.
For the retrofit market, external modifications were determined to be
the most promising path. For these retrofit schemes, the heat in the flue may
be exchanged with one of the following mediums:
• Combustion air (air preheat)
• Fuel (fuel preheat)
• Recirculating house air/water exiting from furnace
• Independent air/water stream
• An intermediary fluid or solid which eventually exchanges heat with
one of the other mediums ("runaround system").
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It was determined that the last four schemes were potentially practical.
The latter two are represented by current devices on the market so were not
considered further although improvements were identified.
Common to all retrofit designs are the following problem areas:
• Pressure drop
• Removal of condensate (if condensing system)
• Corrosion and materials selection
• Thermal stresses and cycling fatigue.
It was determined that in order to make any significant improvement on
efficiency, a compact heat exchanger design and induced draft fan (to compen-
sate for increased system pressure drop) would be required. This heat ex-
changer and the associated duct work would be manufactured from a low grade
stainless steel to avoid corrosion problems. Up to 30,000 Btu/hr could be
recovered from a high temperature flue if the temperature was reduced to the
condensation point so that the latent heat of vaporization as well as the sen-
sible heat could be recovered.
Detailed analysis was undertaken on a plate fin and fin-tube design for
exchange with the exit air or water, or inlet air or water and flue for both
condensing and noncondensing systems. A simple computer program was written
to calculate the performance of any potential surface configuration. From
these calculations, a noncondensing plate fin exchanger with dimensions of
1.2" x 7.1" x 15" was determined to be an attractive arrangement. A larger
unit was designed for a condensing heat exchange surface. These units would
easily fit over the air inlet or outlets of the furnace in much the same man-
ner as a filter.
Bids were solicited from a number of heat exchanger manufacturers and
a broad spectrum of cost were returned. From these data, cost estimates were
made for each scheme for the heat exchanger, required ductwork, insulation,
fan, and installation. From the performance curves, the fuel cost savings per
year was estimated and the payback period determined. The payback period takes
into account the time value of money and assumes that a seven percent rate of
return is available. The calculations show that in terms of payback, the flue
damper is the best buy. It also reveals that the most promising devices are
those that are applied to oil-fired furnaces with high flue gas temperature.
It was also shown that if a 50 percent fuel savings could be achieved
with a new furnace design incorporating higher efficiency heat exchanger,
closure of the flue during non-use periods and furnace modulation, an additional
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$500 to $1000 could be invested as initial capital investment with a payback
in five to ten years.. However, although the large scale economics appear
attractive, formidable social and institutional obstacles would act to prevent
the widespread use of either the retrofit or new furnace designs.
The potential market is, however, rather large if one assumes 20 percent
of the units in the Northeast and Northcentral portion of the U.S. are con-
verted. This assumption would indicate a total conversion of 6.33 million
units and a potential fuel savings by 1982 of 3.02 percent of the U.S. space
heating energy consumption estimate.
In addition to the energy savings aspects of the proposed concepts, the
HELPS study also reviewed the potential for reducing emissions from domestic-
size furnaces. Emissions from gas and oil-fired units account for 1-10 per-
cent of the nation's total emissions. Control strategies for these sources
include fuel substitution, combustion process modification and post-combustion
control. Fuel substitution has been incorporated for quite a few years with
the switch from coal to oil and to gas with a subsequent decrease in emissions,
especially particulates. However, as gas becomes scarce, there may be a trend
back to the other fuels or electricity. Most of the combustion control strat-
egies can be applied to oil-fired units with excess air level adjustment the
primary control for gas-fired units. Research is currently underway by EPA
and AGA on low emission, high efficiency oil and gas burners, respectively.
In all, the feasibility of most of the post-combustion control devices for
residential heating application is unknown.
The results of the present study lead to the following recommendations
for future work of a general nature and for additional studies of a retrofit
scheme:
1. Obtain actual operating data on furnaces by measurement
2. Study British and European design practice where fuel prices
have been historically higher
3. Develop a furnace performance code and compare with 1 above
4. Monitor commercial and legal progress of retrofit devices and
test these units
5. Refine the design of a condensing flue gas heat recovery device.
However, the most fruitful approach would probably be to explore further the
possibility of a new high efficiency furnace design.
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Recommended components in the development of improved furnace designs
include Recommendations 1 and 3 above, followed by tasks to:
6. Predict efficiency of proposed modulation schemes by analytical
techniques; identify cycles to optimize operation; modify cycle
to see how to improve efficiency
7. Analytically predict the effect on heat transfer due to modulating
output,
8. Explore methods of modulation
• Vary gas flow rate
• Use multiple burners in various combinations
• Heat capacitance/hot water systems
9. Develop heat load detector and furnace controller
10. Modify an existing furnace for modulated mode
11. Design a new furnace using either submerged combustion or catalytic
combustion concepts in conjunction with the modulated concept
12. Build and test a prototype unit as described in Recommendation 11
13. Relate the progress of this design and development effort to:
• Commercial and research developments in alternative heat pump/
all electric systems (including solar-assist components)
• Other integrated energy management system programs, including
total-energy and MIUS
• Household energy conservation programs which will be affecting
thermal load data for new construction
With regard to emission control devices two specific areas of study are
recommended:
14. Further define the real contribution of residential emissions to
environmental air quality
15. Further investigate post combustion control devices, if required
16. Define the potential of the modulated furnace concept (Recommenda-
tions 6-11) to reduce the high peak emission associated with start-
up and shutdown periods.
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SECTION 2
INTRODUCTION
This report presents the results of a study to determine the feasibility
of candidate concepts for simultaneous heat and air pollutant emission recovery
from the combustion products of domestic-size furnaces. The major objectives
of the study, separated into report Sections, were as follows:
Definition of Problem and Existing Technology (Section 3)
This Section includes statistics on energy consumption and emissions as-
sociated with domestic furnaces, a review of furnace design practice, and de-
scriptions of commercially available heat recovery devices.
Identification of Alternate Heat Recovery Designs (Section 4)
For typical operating conditions, the most promising concepts identified
in the preliminary phases were characterized in detail, designed, and optimized,
both for retrofit applications and for new installations.
Detailed Analysis of Retrofit Schemes (Section 5)
Two of the most attractive options for retrofit flue gas heat recovery
devices were analyzed in greater depth.
System Cost (Section 6)
Capital and operating costs were estimated in this phase for the systems
designed for retrofit and new installations. Possible impacts of mass produc-
tion were considered.
Control of Air Pollutant Emissions From Residential Heating Equipment (Section 7)
Past, present, and future combustion and post-combustion control methods
we re re vi ewe d.
Potential Market (Section 8)
This final task evaluated the potential of energy recovery devices con-
sidering overall economics (payback periods) and the total size of the potential
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markets. The possible impact of such devices on the U.S. energy situation was
estimated.
Conclusions and Recommendations (Section 9)
Further work that is required to complete the analysis of the costs and
benefits of the HELPS concept is outlined.
In all, the report serves to clarify the energy and environmental impact
of the residential heating sector, as well as to analyze the feasibility of sev-
eral solutions proposed to lessen this impact.
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SECTION 3
DEFINITION OF PROBLEM AND EXISTING TECHNOLOGY
As background to this study a brief survey was made of other work being
done in this field, current furnace design practice, and current heat recovery
devices on the market.
3.1 ENERGY CONSUMPTION AND METHODS OF ENERGY SAVINGS
Table 1 shows the pattern of basic energy consumption in the U.S. for
1968 (Reference 1). This reveals that 11 percent of the total energy consump-
tion went to residential space heating and 6.9 percent went to commercial
space heating. The total residential and commercial energy usages are 19.2
percent and 14.4 percent respectively. Thus, there is a strong incentive to
reduce energy consumption in the residential and commercial sectors and par-
ticularly for space heating.
Table 2 lists a number of government agencies, universities, and trade
associations with ongoing programs in various aspects of energy conservation
in the residential and commercial sector. Entries in the table were compiled
from an Aerotherm survey conducted under this task from testimony presented at
recent hearings on Conservation and Efficient Use of Energy before the Commit-
tee on Government Operations and Science and Astronautics of the House of
Representatives (Reference 2) and from a detailed inventory of current energy
research and development activities compiled by the Oak Ridge National Labora-
tory (Reference 3)*. Table 2 cites only programs which
• Have a direct relevance to this study and which have been personal-
ly investigated in detail in this program, or
• Provide a representative sampling of the total research picture in
residential space heating
This document was obtained late in the course of this brief study, and not
all apparently relevant leads have as yet been pursued in detail.
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TABLE 1
ENERGY CONSUMPTION IN THE U.S. BY END USE 1968
(TRILLIONS OF Btu AND PERCENT PER YEAR)
(Reference 1)
Residential
Space Heating
Water Heating
Cooking
Clothes Drying
Refrigeration
Air Conditioning
Other
Total
Commercial
Space Heating
Water Heating
Cooking
Refrigeration
Air Conditioning
Feedstock
Other
Total
Industrial
Transportation
National Total
Consumption
6,675
1,736
637
208
692
427
1,241
11,616
4,182
653
139
670
1,113
984
1,025
8,766
24,960
15,184
60,526
Percent of
National Total
11.0
2.9
1.1
0.3
1.1
.7
2.1
19.2
6.9
1.1
.2
1.1
1.8
1.6
1.7
14.4
41.2
25.2
100.0
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TABLE 2
STUDIES IN CONSERVATION OF ENERGY FROM
RESIDENTIAL AND COMMERCIAL BUILDING
Contacted
X
X
X
Agency/Asspci ati on/ Insti tuti on
U. S. Department of Commerce
Bureau of Standards - Center for
Building Technology
U. S. Department of Housing and
Urban Development
- Office of the Assistant Secre-
tary for Policy Development and
Research
(Support from NSF-RANN and EPA)
(Hittman Associates)
- Building Technology and Site
Operations
(California State Polytechnic
University)
Nature of Studies
• Computer analysis of building thermal response
• Importance of insulation
• Fenestration and Infiltration
• Equipment and System Options
t Heat pumps
• Heat Exchangers
• Underground heat distribution systems
• Field demonstration projects using energy
conservation projects
t Total energy systems
t Publication of relevant energy conservation
information
• Workshops on energy conservation
• Recommendation of standards
• Identify means for obtaining greater efficiencies
in the consumption of residential power
• Quantify total energy balance in typical residence
• Indentify technical innovation to reduce residential
energy utilization
t Determine the total annual energy savings possible
for several modified versions of the characteristic
house incorporating energy conservation modifications
• Evaluate heating loads in old residential structures
• Research, evaluation of a system of natural air
conditioning with solar energy as the power source
Reference(s)
4, 5, 6, 7, 8
9, 10, 11, 12,
13, 14
2, 17
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TABLE 2 (Continued)
STUDIES IN CONSERVATION OF ENERGY FROM
RESIDENTIAL AND COMMERCIAL BUILDING
Contacted
X
X
Agency/Association/Institution
National Science Foundation/RANN
- Center for Environmental Studies,
Princeton University
- Oak Ridge National Laboratory
U.S. Atomic Energy Commission
- Colorado State University, Solar
Energy Applications Laboratory
- Texas A&M, Texas Engineering
Experiment Station
- University of Wisconsin, Solar
Energy Laboratory
- California Institute of Tech.,
Environmental Quality Lab.
Nature of Studies
• Research project entitled Energy Conservation in
Housing
- Statistically study of a large multiple family
dwelling to determine distribution of energy
utilization
- Development of data acquisition system
- Surveillance of the construction of townhouses
and apartments
Interview and discussion with developers to
develop ideas for improvement for energy
utilization
• Estimate potential monetary and energy savings
through the use of additional thermal insulation in
residential construction
• Develop inventory of current energy research and
development
• Experimental development of a full operational
residential heating and cooling system based on
solar energy
• Development of a compressed-film floating deck solar
water heater
0 Simulation study of solar heating and cooling for
the United States
• Solar/thermal technologies for buildings - technical,
economic and institutional aspects
• Project SAGE - a project to investigate the commer-
cial feasibility of solar assisted gas energy for
water heating in new apartments
Reference(s)
15
16
2
2
2
2
2
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TABLE 2 (Continued)
STUDIES IN CONSERVATION OF ENERGY FROM
RESIDENTIAL AND COMMERCIAL BUILDING
Contacted
X
X
X
Agency/ Association/ Institution
- American Society of Heating
Refrigerating and Air Conditioning
Engineers (ASHRAE)
- University of Florida
- Carnegie-Mellon University
American Gas Association
- Institute of Gas Technology
- Allied Chemical Corporation
- K. Johnson Co.
- Ohio University
- Dynatech Corporation
- A.G.A. Laboratories
Nature of Studies
• Preparation and publication of a ASHRAE Guide
chapter on application of solar energy for heating
and cooling of buildings
• Formulation of a data base for the analysis, evalu-
ation and selection of a low temperature solar
powered air conditioning system
• A selective total energy system for a residential
complex
• Detailed energy usage profile in the Canton/test
homes
• An assessment of selected heat pump systems
• Absorption heat pump program
• New working fluids for Rankine cycle residential
air conditioning system
• New heat pump working fluids
• Thermal refrigeration - direct conversion of heat
energy into refrigeration
• Free piston Stirling engine driven - gas fired air
conditioner
• Basic research in heat transfer
• Design of domestic appliances to use gas at elevated
pressures
• Development of a central heating furnace with ultra
high efficiency (submerged-pulsed combustion device)
Reference^ )
2
2
2
18
18
18
18
18
18, 19, 20, 21,
22
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TABLE 2 (Continued)
STUDIES IN CONSERVATION OF ENERGY FROM
RESIDENTIAL AND COMMERCIAL BUILDING
Contacted
Agency/Association/Institution
Nature of Studies
Reference(s)
- Battelle Columbus Laboratories
• Investigation of thermal fatigue of heat exchangers
in domestic gas furnaces
• Indoor air quality control device
- Thermo-Electron Corporation
• New developments in gas fired appliances; applica-
tion of Rankine cycle engines to residential gas
air conditioning
- AiResearch Manufacturing Co.
• Development of a heat actuated space conditioning
unit for commercial applications - utilization of
a Brayton cycle engine
Pope, Evans and Robbins
• Economic advantage of central heating and cooling
systems
University of Oklahoma Research
Institute/Public Service Co. of
Tulsa
• A comparitive study of energy usuage
American Society of Heating,
Refrigerating and Air Conditioning
Engineers (ASHRAE)
- Edison Electric Research Corp.
(York Research Corp.)
• Measurement of the performance of the ASHRAE infra-
red space heating system
• Determination of specific heats of building
materials
- University of Florida
Determination of shading coefficients for reflective
coated glasses with draperies
ASHRAE Research and Technical
Committee, Task Group on Energy
Conservation
A task group on energy conservation has been estab-
lished to evaluate the manner in which basic energy
sources can be conserved through the more effective
utilization of energy in residential commercial in-
stitutional and industrial buildings. Conducts sym-
posia, publishes papers by members, e.g. reference
18
2
23
23
24, 25
-------
TABLE 2 (Continued)
STUDIES IN CONSERVATION OF ENERGY FROM
RESIDENTIAL AND COMMERCIAL BUILDUNG
Contacted
Agency/Association/Institution
Nature of Studies
Reference(s)
25 Symposium on Heat Recovery. Update ASHRAE Guide
and data book to reflect latest technology on con-
servation of energy. Provides component index of
technical articles published by the Society and
presented in the Journals.
- ASHRAE Standard 90-P Committee
Has taken the NBS document on design and evaluation
criteria for energy conservation mentioned above
and drafted an ASHRAE Interim Standard on Energy
Conservation for use by the National Conference of
States on Building Codes.
Long Island Lighting Co.
• Electric energy utilization study of the generic
environmental impact of electric versus oil space
heating, i.e. what effect electric heat will have
on air quality
Stevens Institute of Technology
• Determine efficiency fuel oil burners in the field
and difference between makes.
• Determine method of maintaining efficiency
Pennsylvania Power and Light Co.
- Franklin Institute Res. Labs.
Assist in the design of energy conserving home
incorporating features such as heat pumps, waste
heat recovery, supplementary solar heating and
thermal energy storage
Construction and testing of the above house
Consolidated Natural Gas Service
Co. (Thermo-Electron Corp.)
• Development of a compact liquid heater for indus-
trial and commercial heat transfer applications
Oklahoma Gas and Electric Co.
• Development of a computer oriented system for
determining building energy requirements and an
economic analysis of their requirement
5, 26, 27
-------
TABLE 2 (Concluded)
STUDIES IN CONSERVATION OF ENERGY FROM
RESIDENTIAL AND COMMERCIAL BUILDING
Contacted
X
X
X
X
Agency/ Association/ Institution
Southern California Gas Co.
- Thermo-Electron Corporation
Environmental Protection Agency
- Contractor
- Rocketdyne
- Aerotherm/Acurex
Nature of Studies
• Similar to above; development and distribution of
E cube computer program to determine energy con-
sumption of a building. Also sponsored by A.G.A.
t Application of heat pipe technology to appliances
• Conducted study of various strategies for reducing
national energy demand
• Development of optimum oil-fired burner and furnace
package
• HELPS
Reference(s)
28
2, 29
30
39
-------
There are many more programs dealing with solar heating and typical energy uti-
lization of family dwellings.
A large number of these studies are concerned with the overall reduction
of energy for both heating and cooling through
• Better and more insulation
• Lower indoor temperature levels for heating
• Higher indoor temperature levels for cooling
• Setback of temperature at night
• Closing off of unused rooms
• Reduced lighting
• Addition of insulating glass or storm windows
• Better window caulking
• Insulation of heating ducts
• Improved maintenance of heating equipment
• Better management of doors, windows, and drapes
• Installation of automatic pilots
• Adjustment of ventilation systems
• Minimized use of portable electric heaters by improving main heat-
ing system
• Replacement of inefficient heating systems with systems of higher
efficiency
• Systems modification for zone control
• Means to transfer heat from the center of a large building to the
cool periphery
• Automatic door closures
• Installation of heat recovery devices (References 6, 10, 30)
For example, the National Bureau of Standards estimated that the winter heat-
ing loads could be reduced by as much as 40 percent if all these options were
incorporated (Reference 6). To recover heat from stacks Reference 6 mentions
heat pipes, runaround circuits and automatic stack dampers. For ventilation
systems Reference 6 recommends runaround circuits, thermal wheels, heat pipes,
heat pumps, and other heat exchange circuits. However, no details were given
of these systems.
16
-------
The Hittman Report on residential energy consumption (Reference 10)
came to the following conclusions:
• Infiltrated air was the greatest load component for both heating
and cooling
• Conductive losses thorugh the walls and windows ranked second and
third, respectively
• Losses through ceiling, floors and doors were relatively small.
Table 3 shows the estimated annual energy savings by incorporation of
various energy conservation modifications as presented by Siedel, et al.
(Reference 30). This shows that in terms of saving energy, heat recovery of
the furnace flue represents the largest single contributor. This figure of
28 percent, however, includes recovery of the latent heat of vaporizations
and incorporation of a furnace flue shutoff device. A more detailed break-
down of these savings is available from the Hittman Report and is shown in
Table 4.
This shows that a noncondensing heat recovery device can save about
9 percent of the heating load and only 3.6 percent of the total energy con-
sumption of the house.
Research by the Oak Ridge National Laboratory shows even greater poten-
tial savings from increased insulation (Reference 16). They estimate that a
gas heated home could realize energy savings as high as 30 to 50 percent at no
economic penalty through increased insulation in floor, walls, and ceiling.
For a more detailed discussion of the various strategies for energy
reductions, the reader is referred to the EPA document on Energy Conservations
Strategies (Reference 30) and the NBS document on Technical Options for Energy
Conservation in Buildings (Reference 6) as well as the Hittman-HUD reports
(References 14-16).
Energy conservation strategies discussed by the American Society for
Heating Refrigeration and Air Conditioning Engineers (ASHRAE) (References 24,
25) have been primarily oriented towards commercial and institutional buildings.
However, their recent development of draft interim standards, ASHRAE Standard
90P (Reference 27), for energy conservation in new buildings (the implementa-
tion of recommendations by the NBS) includes all building and equipment sizes.
This standard is under open review to be completed September 1974. These new
standards cover the following areas:
17
-------
.TABLE 3
SAVINGS FROM MODIFICATION OF CHARACTERISTIC DESIGN
(Reference 30)
Load or MOD
Furnace Reference Load
Air Conditioner Load*
Furnace Recovery
High Performance Unit**
Furnace Pilot Elimination***
Open Air Cycle
Storm Windows
25% Window Area Reduction
Cinder Block Insulation
High Capacity Wall
Sealed Furnace Air Supply
Sealed Hot Water Air Supply
Clothes Dryer Recovery
Double Door Design
Revolving Door Design
Ducted Oven Design
Ducted Refrigerator
Attic Ventilation
Winter Load
Percent
Saved
100.0
27.9
3.4
15.8
19.1
7.1
2.6
4.6
1.7
2.4
1.6
2.6
MBTU
Saved
101.4
28.3
3.5
16.0
19.4
7.2
2.6
4.7
1.7
2.4
1.5
2.7
Summer Load
Percent
Saved
100.0
33.3
8.3
8.1
9.5
.6
.8
1.9
3.8
6.9
1.9
7.0
.5
MBTU
Saved
10.8
3.6
1.0
.9
1.0
.1
.1
.2
.4
.7
.2
.8
.1
*
- Based on 8.0 Btu/watt-hr performance
**
- Based on 12.0 Btu/watt-hr performance
***
- Based on a 1000 Btu/hr pilot light
18
-------
TABLE 4
BREAKDOWN OF ENERGY SAVINGS FOR FURNACE RECOVERY AND FLUE DAMPER
(Reference 10)
"Characteristic House Energy Consumption"
(Therms)
Annual Consumption
Heating
1044
Cooling
388
Total
Heating & Cooling
1432
Lights &
Appliances
1174
Total
2606
Heat Recovery Device
Noncondensing
Heat Recovery Device
Condensing
Furnace Flue Closure
Heat Recovery & Furnace
Flue Closure
Noncondensing
Heat Recovery & Furnace
Flue Closure
Condensing
Energy Therms
94
~ 194
- 100
194
294
Percent of a
9
18.6
9.6
18.6
28.1
Percent of b
6.6
13.5
7.0
13.5
20.5
Percent of c
3.6
7.4
3.8
7.4
11.28
19
-------
• Insulation
• Procedures for determining heating or cooling system capacity
• Temperature control, single zone and multiple zone
• Humidity control
• Controlled temperature setback during non use periods
• Simultaneous heating and cooling
• Reheat
• Illumination
• Energy recovery (air exhaust-makeup systems only)
• Air infiltration
• Procedures for HVAC zoning
• Duct air leakages
• Automatic ignition system
• Recommended equipment efficiencies (efficiencies should comply with
current American National Standards Institute (ANSI) for heating
equipment; to be discussed in Section 3.4).
• Prevention of off cycle air flow heat loss
The later criterion recommends that all combustion heating equipment
with greater than 250,000 Btu/hr input should be equipped with devices, such
as automatic vent dampers, to minimize air flow through the combustion chamber
during off cycles. These standards will significantly affect the energy con-
sumption of new residential construction through the areas of better insulat-
tion and limitations of air infiltration. It is estimated that through these
two areas alone from 30 to 50 percent of the heating load could be saved de-
pending on location of total number of infiltration points. An overview of
the Energy Conservation Standard recently appeared in the ASHRAE July 1974
issue (Reference 26).
Although the quantitative results of these various studies differ ac-
cording to differences in assumptions, the results agree that improvements in
furnace efficiency (or, alternatively, flue gas energy recovery) can provide
significant energy savings in a major energy consumption area.
20
-------
3.2 FURNACE TYPES
The first step in designing a heat recovery device is to determine the
types and distributions of furnaces across the U.S. ASHRAE, AGA, GAMA, furnace
manufacturers and other trade associations consistently referred us to the
1970 U.S. Census information as the most detailed breakdown available.*
Table 5 from Reference 31 presents the 1970 U.S. Census information on the
distribution of residential heating systems for the entire U.S. This informa-
tion is divided into heating system type, fuel, owned or rented, percentage of
total population of furnaces and the ranking.** Unfortunately, there was not
a good breakdown on definitions of "other heating equipment", which may in-
clude room heaters with flue, room heaters without flue, fireplaces, stoves or
portable heaters. This table shows that the principal heating method for the
U.S. as a whole is the gas fired warm air furnace (31.6 percent; this includes
both gravity type and forced air systems). Oil fired hot water or steam ranks
second with 12.29% of the heating systems. There are, however, considerable
variations in the mix of heating system types across the country. Figures 1
and 2, also from the U.S. Census data, show the gross distribution of heating
equipment types and housing fuels for four regions of the country. These fig-
ures show that in the Northeastern section of the country, 56.2 percent of the
homes are steam or hot water heated and that 54.4 percent of all the furnaces
are oil fired. By contrast, 41.1 percent of the homes in the West are warm air
furnaces and 71.1 percent are gas fired.
Table 6 from data published by the Gas Appliance Manufacturers Associa-
tion (GAMA) show that the trend in the last ten years is toward gas fired
forced air systems, which account for 46.2 percent of the furnaces sold in
1973 (Reference 32). This is further substantiated by U.S. Census data shown
in Table 7 (Reference 31), which indicates that for houses built prior to 1939
almost 30 percent of the warm air furnaces are oil fired compared to approxi-
mately 15 percent for houses built during the period 1960-1970. These data
show conditions at the time of the 1970 Census which no doubt include a consi-
derable number of replacement units. The older more inefficient furnace are
most amenable to retrofit devices. Unfortunately, one cannot determine direct-
ly the furnace age from these statistics. These tables and figures thus indi-
cate that both gas and oil fired central warm air and hot water furnaces should
Some large manufacturers indicated they had similar information but that it
was considered proprietary.
The two categories, "built in electric unit" and "none", appearing in the U.S.
census tables of Reference 31 have been omitted from Table 5.
21
-------
TABLE 5
RESIDENTIAL HEATING SYSTEM IN THE U.S. 1970 CENSUS
(Reference 31)
Steam or Hot Water
Gas
Fuel Oil
Coal or Coke
Wood
Electricity
Bottled, Tank, or LP Gas
Other Fuel
Warm Air Furnace
Gas
Fuel Oil
Coal or Coke
Wood
Electricity
Bottled, Tank, or LP Gas
Other Fuel
Floor Wall or Pi pel ess
Gas
Fuel Oil
Coal
Wood
Electricity
Bottled, Tank, or LP Gas
Other Fuel
Other Heating Equipment
Gas
Fuel Oil
Coal
Wood
Electricity
Bottled, Tank, or LP Gas
Other Fuel
Owner
2,415,455
3,687,913
183,293
84,758
32,205
13,968,429
4,746,515
428,130
966,673
24,162
2,672,364
414,983
40,637
273,788
3,447
3,213,424
1,650,175
320,499
438,330
1,406,157
3,683
Rented
2,694,746
3,463,636
407,821
75,334
175,181
4,389,501
1,284,546
155,518
224,906
20,686
1,858,511
156,663
20,644
103,834
3,673
3,801,315
1,069,039
264,410
355,578
670,498
3,249
Total
5,110,201
7,151,549
591,114
160,092
207,366
18,357,930
6,031,061
583,648
1,191,579
44,848
4,530,875
571,646
61,281
377,622
7,120
7,014,739
2,719,214
584,909
793,908
2,076,655
6,932
58,174,289
%
8.78
12.29
1.02
0.28
0.36
31.56
10.37
1.00
2.04
0.08
7.79
0.98
0.10
0.65
0.01
12.06
4.67
1.00
1.36
3.57
0.01
99.98
Rank
5.
2.
1.
4.
9.
6.
3.
7.
10.
8.
22
-------
Northeast
Steam or Hot Water
Northcentral
Southwest
West
Figure 1. Heating Equipment, by Regions: 1970-Percent (All Occupied Units)
(Reference 31)
|444444^4*%^444 ie.o%
m 5.9% \m 5.1% ]
Warm-air Furnace
I444444i 31.6%
44444<*4*64. 5^1 4444444 34. 9;: 14444 4444*4 m
Built-in Electric Units
\4 2.6%
4 2.3%
44 7.4% |*4 8.8%
Floor, Wall, or Pi pel ess Furnace
i 1.7%
4 4.3%
44i 10.8% 4444* 22.1%
Room Heaters with Flue
m 5.3%
mm 10.2%
444 15.7% 444 14.2%
Room Heaters without Flue
1 1.1%
< 1.3%
444 14.8% 4 2.8%
Fireplaces, Stoves, or Portable Heaters
1 1.3%
i 1.4%
mm 0:6% tf 2.2%
None
| 0.1%
0.0%
I 0.6% 4 2.2%
4 = 5%
-------
to
**•
(Northeast
Utility Gas
Northcentral
Southwest
1 4444444* 37. id 44444464C664 444*44^450.0%
West |
444444*04*1 .B|
Fuel Oil, Kerosene, etc.
1 44444404*54.4%! 4444 19.6%
44*14 18.9%
441 8.8% |
Coal or Coke
|f 3.5%
fl 3.3%
« 3.2%
1 0.7% |
Mood
|l 0.2%
1 0.4%
4 2.9%
1 1.3* 1
Electricity
I* 3.1%
43.1%
444 13.2%
44i n.7% I
Bottled, Tank, or LP Gas
ll 1-1%
4l 6.3%
44l 10.9% 14 3.8% I
Other
If 0.7%
1 0.5%
1 0.2%
1 0.4% I
None
ll 0.1%
I 0.1%
• 0.6%
< 2.2% 1
Figure 2. House Heating Fuel, by Regions: 1970 Percent (All Occupied Units)
(Reference 31)
-------
TABLE 6
FURNACE SYSTEMS SOLD (GAMA)
(Reference 32)
Gas Fired Forced Air
Floor - Gas
Vented Wall Furnace - Gas
Oil Fired Cent.
Oil Fired Floor & Wall
Gas Fired Direct Heating
Oil Fired Direct
Coal & Wood Direct
Totals
1973
#
2,261,600
42,900
719,660
734,000
N/A
708,300
197,600
228,200
4,892,260
%
46.2
0.9
14.7
15.0
14.5
4.0
4.7
100%
1963
#
1,394,300
77,200
448,100
520,200
30,300
1,323,800
417,000
537,400
4,748,300
%
29.4
1.6
9.4
11.0
0.6
27.9
8.8
11.3
100%
25
-------
KJ
CTi
TABLE 7
(Reference 31)
Year Structure Built for Owner and Renter Occupied Housing Units by Heating Equipment
1970
Household Head—All Races
[Dora bos«j on sample, see text. For meaning of symbols, see text]
United States
HEATING EQUIPMENT BY HOUSE
HEATING FUEL
Wood
Electricity ,. .
Bottled tank or LP gas
Other fuel .. ....
None ~
Utility gas
Wood
Bottled tank or LP gos .
None _ _ .
flwr, wall, or |Hp«W§t fumott ..
Utility gas
Wood - -- -
Other fuel
Utility gas -- ' --
Wood - -
Other fuel .
None - -
TOTALS
J/TOTAL
Owner occupied
Totol
6 403 624
2 415 455
3 687 913
183 293
B4 758
32 205
20 884 609
13 968 429
4 746 515
428 130
750 700
. 966 673
24 162
3 404 219
2 672 364
414 983
40 637
274 788
3 447
7 241 305
3 213 424
1 650 175
320 499
438 330
209 037
1 406 157
3 683
37 935 757
100
I960 to
March
1970
1 130 071
505 486
582 870
6 295
30 033
5 387
6 933 059
4 921 180
1 058 415
16 676
504 785
481 897
5 106
463 420
284 025
: 99 701
2 093
76 939
662
1 051 219
354 334
248 853
27 860
67 875
48 968
X2 735
594
9 632 769
25.4
1950
to
1959
1 240 413
372 917
836 556
13 609
12 474
4 857
5 875 640
4 155 148
1 365 369
45 265
143 320
160 884
5 654
1 164 639
950 491
141 154
4 411
67 757
826
1 511 323
690 623
341 8i7
40 105
67 457
64 887
305 513
916
9 792 015
25.8
1940
to
1949
601 621
200 555
379 325
11 813
6 659
3 269
2 158 617
1 411 688
586 325
52 093
41 875
63 335
3 301
725 396
622 917
60 527
5 509
35 838
605
1 242 996
611 441
235 636
49 799
72 549
39 804
233 203
564
4 728 630
12.5
1939
or
earlier
3 431 519
1 336 497
1 889 162
151 576
35 592
18 692
5 862 293
3 480 413
1 736 406
314 096
60 720
260 557
10 101
1 052 764
814 931
113 601
28 624
94 254
1 354
3 435 767
1 557 021
823 869
202 735
230 449
55 378
564 706
1 609
13 782 343
36.3
Renter occupied
Totol
6 816 718
2 694 746
3 463 636
407 821
75 334
175 181
A 616 735
4 339 501
1 284 546
155 518
541 578
224 906
20 686
2 143 325
1 858 511
156 663
20 644
103 834
3 673
6 3O6 399
3 80! 315
1 069 039
264 410
355 578
142 810
670 498
3 249
21 883 677
. 100
1960to
March
1970
1 014 359
559 174
399 179
11 408
13 510
31 588
2 282 206
1 527 538
243 604
4 307
422 922
76 950
6 885
464 856
4)0 865
29 343
991
22 563
1 094
634 368
396 5^8
88 790
13 288
24 136
24 654
86 747
205
4 396 289
20.1
1950
to
1959
6-96 233
267 402
379 730
17 840
9 Oil
22 250
1 127 94O
794 339
225 578
8 126
62 401
34 505
2 991
596 720
531 263
4] 509
1 252
22 003
693
955 817
591 460
156 262
23 427
35 542
33 283
115 333
510
3 376 710
15.4
1940
to
1949
7B2 369
297 964
403 094
44 394
11 408
25 509
70S 771
489 389
156 177
15 064
21 145
21 546
2 450
442 833
394 156
28 025
2 524
17 543
585
1 144 942
722 745
174 148
37 736
53 855
30 453
125 290
635
3 075 915
H.I
1939
or
earlier
4 323 257
1 570 206
2 281 633
334 179
41 <05
95 834
2 500 818
1 578 235
659 187
128 021
35 110
91 905
8 360
638 916
522 227
57 786
15 877
41 725
1 301
3 571 77J
2 090 562
649 839
169 909
•242 045
54 390
343 123
1 899
11 034 763
50.4
-------
be considered. Since noncentral systems are so widely distributed in types,
they will be eliminated from further discussion.
3.3 FURNACE DESIGN PRACTICE
With the furnace designs to be considered now determined, the next step
is to define a characteristic design for each of these furnace categories.
3.3.1 Central Air Gas Fired
Figures 3 and 4 show some typical gas fired forced central air sys-
tems which account for the single largest category.* There are generally
three forced air types: upflow, downflow, and horizontal. There is lit-
tle variation among manufacturers in the overall layout. Typically for an
upflow unit, the house circulating air enters the bottom or side of the unit,
flows through the main circulating fan, then to the heat exchanger and usu-
ally out the top to the distribution ducting. The gas burners are natural-
ly aspirated types consisting of three to four venturies, with distribution
pipes consisting of rows of small orifices. The primary air is drawn into
the venturi by the gas presssure and premixes with the gas prior to ignition.
The primary air/fuel ratio can be controlled through small shutters at each
venturi. Secondary air from the furnace room enters around the burners to
quench the peak flame temperature and allow complete combustion. The flue
products then proceed upward through a parallel flow heat exchanger and exit
into a common plenum. Units always include draft diverters which dilute the
flue gas stream and prevent downdrafts from blowing out the pilot. Typical
operating conditions are tabulated in Table 8.
Several comments concerning this data of Table 8 are appropriate.
First, the wide range in excess air levels is due to variations in installa-
tions and meterological conditions. Second, the combustion chamber pressures
are quite low due to the naturally aspirated burners. Consequently, the heat
transfer area is quite large on the flue gas side to prevent excessive pres-
sure drop. This results in fairly low heat transfer coefficient on the hot
side and consequently fairly large surface areas. The furnace relies on the
stack to create sufficient draft to draw the secondary air through the fur-
nace. Furnace manufacturers frequently claim that reduction in the stack
*
In the past there were also a considerable number of gravity or natural draft
gas and oil fired central air systems. These have fallen out of favor due to
the rather large ducts furnace volume required and higher cost.
27
-------
TABLE 8
TYPICAL OPERATING CONDITIONS*
Assume 100,000 Btu/hr
Recirculating Air Flowrate (SCFM): 800-1200 SCFM
Excess Air: 20% - 500%
Flue Exit Diameter: 3-1/2" - 5"
Heat Exchange Area: ~ 30 ft2 - 35 ft2
Overall Heat Transfer Coefficient: 2 Btu/hr-ft2°F - 3 Btu/hr-ft2°F
Exit Flue Gas Temperature (Before Draft Diverter): 450 - 650
Draft Diverter Dilution Air Flow Percent of Flue: 20% - 50%
Combustion Chamber Pressure: ±0.2 "H20
Temperature Rise on Air Side: 70°F - 75°F
Overall Steady State Efficiency: 75% -
if
Data is compiled from discussion with manufacturers and from
References 33, 34, 35, 36, and 37.
**
New installation must meet ANSI standards of 75 percent.
28
-------
i
il
Figure 3. Gas Fired-Forced Air Furnaces
(Courtesy Sears Roebuck & Co.)
-------
'••
• •
UNIVERSAL SLOTTED PORT STEEL
BURNER
Burns Natural And Liquefied Petroleum
Gases. Stainless Steel Head.
UNIQUE PATENTED DRAFT DIVERTER
HEAT EXCHANGE
Figure 4. Gas Fired Forced Air Down-flow Furnace and Details of Components
(Courtesy Coleman Co. and Westinghouse)
-------
temperature below 300°F will result in insufficient draft for the burners and
cause condensation in the stack. Simple calculations reveal these statements
to be approximately correct (see the appendix for calculations). The shape of
the heat exchanger in Figure 4 should also be noted. Notice that the base of
the unit near the burners is flared to prevent flame impingement on the carbon
steel heat exchange surface. It is possible that if insufficient secondary
air is drawn in around this surface, it could result in excessive temperatures.
The general design method for these furnaces was characterized through
discussions with 19 furnace manufacturers and through the presentations in the
Gas Engineers Handbook, ASHRAE Handbook of Fundamentals, ASHRAE Guide and Data
book and the Handbook of Air Conditioning, Heating and Ventilating (References
33-36). In summary:
• The procedure is largely empirical and relies on testing and modi-
fications of experimental units to meet AGA/ANSI standards (see
Sections 3.3.5) .
• Efficiencies are checked on the basis of exit temperature and CO_
level using charts published by the AGA or ASHRAE (see Section 3.3.5.
on efficiency calculations).
• An overall heat transfer coefficient of 2.7 Btu/hr-ft2°F is recom-
mended by ASHRAE.
• Empirical correlation are available for stack sizing (see
References 36, 38).
3.3.2 Central Air-Oil Fired
Figure 5 shows several typical oil-fired forced air furnaces. From the
outside, these furnaces look very similar to the gas-fired units and are now
being made with overall volumes not much greater than the gas-fired units.
There is a considerable internal difference. The heat is usually supplied by
a gun type oil burner as pictured in Figure 6. This unit consists of a com-
bustion air blower, motor, damper, fuel pump, ignition system, main air tube
and swirlers, and fuel nozzle(s). The fuel flow rate is controlled by the
orifice size in the oil nozzle, the total air flow rate by the blower and damp-
er. The proper air/fuel ratio is adjusted using the damper until minimum CO
and smoke levels are achieved.
The burner is mounted in a refractory or refractory felt lined combus-
tion chamber which is cooled by the house circulating air. From the combus-
tion chamber the flue gases pass through a gas to air heat exchanger and fi-
nally out the stack. Generally there is no draft diverter in the flue because
there is no pilot flame and a forced draft system is used. The burner blower
31
-------
•--•
Figure 5. Oil Fired Central Air Furnaces
(Courtesy Day & Night Co.)
-------
Figure 6. Typical Oil Burners
(Courtesy Johnson Oil Burner Co.)
•
-------
may supply the full pressure to exhaust the flue from the stack or it may
rely partially on the bouyancy forces downstream of the furnace. Table 9
lists typical operating condition.
Again the design procedure is quite empirical and relies on prototype
development, experience, and testing.
Efficiency and standards for construction are set by Underwriters
Laboratory and ANSI.
3.3.3 Hot Water-Gas Fired
Figure 7 shows a typical gas fired-hot water or hydronic heater. New
units are usually considerably more expensive than forced air systems and
therefore are now being made in the larger size ranges of 130,000 Btu/hr and
higher. However, old units are still quite prevalent in the Northeastern
and Northcentral regions of the U.S. The gas systems on the new units are
quite similar to the central air furnace utilizing the naturally aspirated
burners. Typical operating and design conditions for both oil and gas sys-
tems are given in Table 10.
Heat transfer area is governed by the gas side transfer coefficient
which is once again limited by the pressure drop requirements of the naturally
aspirated burners. Further details on the design procedures of these units
were not investigated.
3.3.4 Hot Water-Oil Fired
Figure 8 shows the oil fired-hot water system. Again, although quite
prevalant in older homes in the Northeast and Northcentral States, they are
now quite costly and are limited to the larger size ranges. The design ap-
proaches that of larger hot water boilers and these units are similar in some
respects to the oil fired central air designs in that they employ a refractory
lined combustion chamber followed by the heat exchange surface. However, no
draft diverter is required. It has been reported that poor matching of burner
and combustion chamber requirements occurs between the burner manufacturer and
furnace manufacturer (Reference 39). Typically, considerable leakage of se-
condary air into the firebox can occur, lowering flame temperatures. In many
cases this is necessary to prevent damage to the combustion chamber but leak-
age probably results in overall lower furnace efficiency.
34
-------
TABLE 9
OIL FIRED CENTRAL AIR SYSTEMS
Typical Operating Conditions
Recirculating Air Flow: 800 -1200 SCFM
Excess Air: 10% - 100%
Flue Exit Diameter: 5" - 7"
Heat Exchange Area: 20 ft2 - 30 ft2
Overall Heat Transfer Coefficient: 2 Btu/hr-ft2°F - 3 Btu/hr-ft2°F
Exit Flue Gas Temperature: 500°F - 900°F (Older Units)
Combustion Chamber Pressure: .05 "H20 - 0.2 "H?0
Temperature Rise on Air Side: 75°F - 80°F
Overall Steady State Efficiency: 70% - 75%
35
-------
galvanized and baked
enamel jacket,
100% copper
and bronze waterways
massive bronze headers—
easily removable
heat exchanger
inspection panel
corner sealed & interlocked
combustion chamber
high velocity water flow
Raypak "V" baffles
1" integral-finned
copper tubing
modulating valve
totally enclosed
automatic controls
removable door for access to
slide out burner drawer
'precision titanium-
stainless steel burners
Figure 7. Gas Fired Hydronic Boiler (courtesy of the
Raypack Co.)
-------
TABLE 10
OIL AND GAS FIRED-HOT WATER
TYPICAL OPERATING CONDITIONS OF DESIGN PRACTICE
100,000 Btu/HR INPUT
Recirculating Water Flows:
Excess Air (percent):
Flue Exit Diameter:
Exit Flue Gas Temp (Upstream Draft Diverter):
Exit Flue Gas Temp (Downstream Draft Diverter):
Combustion Chamber Pressure:
Temperature Rise on Water Side:
Overall Steady State Efficiency:
Gas
3-15
20-500
3 1/2-5
500-600
300-400
.05-2
10-40
75-80
Oil
3-15
30-100
3 1/2-5
400-600
-
0.2
10-40
70-75
37
-------
HYDRO-WALL DESIGN
TOP CLEAN-OUT OPENINGS
Figure 8. Oil Fired-Hydronic System
(Courtesy of Weil-McLain Co.)
:
-------
3.3.5 Furnace Efficiencies and Standards
As stated in the previous sections, furnaces must meet certain stan-
dards sanctioned by the AGA through ANSI or by U.L. to carry their seals.
These institutes are composed of members from trade association and
government agencies, and insurance organizations. Each standard is developed
and updated by a committee composed of representatives of concerned groups.
Each standard itself is a 30- to 40-page document which covers nearly every
aspect of the system from the efficiency to motors, wiring, sheet metal, bur-
ners, and safety systems. Table 11 gives a brief listing of the various ANSI
and U.L. standards pertinent to this study and the recommended efficiencies.
It will be noticed that the efficiency for gas fired forced air central fur-
naces is 75 percent. However, standard practice in the industry is currently
about 80 percent.
These efficiencies are determined, however, under controlled steady
state conditions. Actual efficiencies in the home will depend on the given
installation (closet, basement, garage), air flow to the furnace, wind and
atmospheric conditions, effects of cycling to satisfy heating load, pilot
usage, standby losses, condition of air filter and air settings on the furnace.
In addition, the furnace efficiencies will usually degrade with time due to
accumulations of soot, nozzle fouling, filter plugging, fan belt slippage, and
similar degradation effects.
In 1966 the AGA laboratories conducted performance tests on identical
gas and oil fired hot water boilers. They attempted to quantify the "service
efficiency" to take into account these losses. Table 12 shows the results of
these tests (Reference 40). These data show the service efficiencies to be
1 to 8 percentage points below the thermal efficiency depending on cycle on/
off time. In general, the data showed the gas furnace to be slightly more
efficient than the oil units while not deteriorating with age. Another in-
teresting study in 1970 by Strieker (Reference 41) attempted to measure the
efficiencies of two forced air furnaces in the "as found" condition in the
field over a six-month period. Figures 9 and 10 from this study show the
typical temperature rise on the air side during a cycle. Figure 11 shows the
resulting average energy balance for the oil fired and gas fired furnaces.
The seasonal efficiencies were calculated to be 61 percent for oil and 62 per-
cent for gas. The authors warn that these values cannot be considered typical
and that a large number of furnaces and structures must be studied to obtain
typical values of seasonal efficiency.
39
-------
TABLE 11
LISTING OF STANDARDS FOR HVAC
EQUIPMENT WHICH INCLUDE EFFICIENCY
ANSI Z31.11 - 1974
Gas-Fired Room Heaters
Volume I (Z21.11.1) Vented Room Heaters, Greater than 20,000 Btu/hr -
Efficiency 70 percent based on total volume of gas; Less than
20,000 Btu/hr - Efficiency 65 percent.
Volume II (Z21.11.2) Unvented Room Heaters - 1974 - Performance - No
number for efficiency.
ANSI Z21.13 - 1972
Gas-Fired Steam and Hot Water Boilers
Shall have a thermal efficiency of 75 percent based on total heating
value of the fuel.
ANSI Z21.34 - 1971
Gas-Fired Duct Furnaces
Thermal efficiency of 75 percent based on total heating value of
fuel.
ANSI Z21.43 - 1968
Unvented Gas-Fired Infrared Radiant Heaters
Radiant efficiency of at least 35 percent.
ANSI Z21.44 - 1973
Gas-Fired Gravity and Fan Type Sealed Combustion System Wall Furnaces
Gravity type - Efficiency 70 percent based on total heating value
of fuel.
Fan type - Efficiency 75 percent based on total heating value of fuel,
ANSI Z21.47 - 1973
Gas-Fired Gravity and Forced Air Central Furnaces
Gravity type - Thermal efficiency 70 percent based on total heat
value of fuel.
Fan type - Thermal efficiency 75 percent based on total heating
value of fuel.
ANSI Z 21.48 - 1973
Gas-Fired Gravity and Fan Type Floor Furnaces
Gravity type - Efficiency 65 percent based on total heating value
of fuel.
40
-------
TABLE 11 (Concluded)
Fan type - Efficiency 70 percent based on total heating value of fuel.
ANSI Z21.51 - 1971
Vented Gas-Fired Infrared Radiant Heaters
Efficiency - shall have a radiant efficiency of at least 35 percent.
ANSI Z21.52 - 1971
Gas-Fired Single Firebox Boilers
Steam and hot water boilers shall have efficiency 75 percent based on
total heating value of fuel.
ANSI Z21.53 - 1967
Gas-Fired Heavy-Duty Forced Air Heaters
Shall have thermal efficiency of not less than 75 percent based on
total heating value of fuel.
ANSI Z91.1 - 1972
Oil-Powered Central Furnaces
Performance - Output capacity in Btu/hr 0.75 times input.
41
-------
TABLE 12
THERMAL AND SERVICE EFFICIENCIES OF RESIDENTIAL HOT WATER BOILERS
(Boiler A Differs From Most Contemporary Oil-Fired Equipment)
(Reference 40)
Boiler and
Condition
Boiler A (Oil)
- New
- After 6 mos.
- After 10.5
mos.
Boiler B (Oil)
- New
- After 6 mos.
Boiler C (Gas
- New
Boiler D (Gas)
- New
- After 6 mos.
Thermal
Eff., %
76.2
74.8
73.43
72.60
71.50
76.80
76.78
76.78
Standby Loss
% of Input
2.02
2.40
3.00
3.14
Service Eff. %
("On/Off" Time, Min.)
20/10
75.50
74.10
72.87
71.50
70.30
75.30
75.90
75.90
15/15
74.80
73.30
72.06
70.00
68.80
73.70
74.20
74.20
10/20
71.30
70.00
68.78
67.10
66.00
68.40
70.40
70.40
NOTE: Electric consumption of oil boiler accessories included in
input.
-------
100
Area Under Curve
Represents 2.42 KWH
Area Represents
0.145 KWH
Blower Starts
Blower Stops
Extrapolated to
Zero Temp. Rise
10.5 14.0 17.5
Blower on Time in Minutes
21.0
24.5
Figure 9. Temperature Rise Across Oil Furnace During a Typical Normal Cycle
(Reference 41)
-------
100
O)
o
to
10
o
i.
o
ef.
QJ
Q.
Ol
OJ
Ol
ro
s_
Ol
80
60 -
40
20
0
Fire Stops
Area Under Curve
Represents 6.51 KWH
Area Represents
0.103 KWH
Extrapolated to
Zero Temp. Rise
9 12
Blower on Time in Minutes
15
18
21
Figuro 10. Temperature Rise Across Gas Furnace During A Typical Normal Cycle
(Reference 41)
-------
Furnace Hrat Output
Measured in Duct System
52.9% (+J.7)
Combustion
A1r: 1.91
Contained
Flue-Gas as
leaves furnace
Heat Required
to Vaporize Oil: 0.6*
Recovered by
Stack-Pipe Loss
Tol.il IKrftil Mr«t:
(•:>.;)
Electrical Input-
Remainder After
Blower Stops
Furnace Heat Output
Measured in Duct System
64.5* (+3.2)
Combustion:
Air 2.2*
Flue-Hater
9.8* (+0.5)
/Heat Contained 1n .
Flue-Gas as 1t \
Leaves Furnace:
31.6* (+1.6)
Heat That Leaves House
Via Chimney: 29.8* (+1.5)
Mlscellaneout: 0.9X
Total Useful Heat:
67.1* (+3.2)
Recovered by
Stack-Pipe Loft
Remainder After
Blower Stops
Electrical Input
Total Accounted Energy:
Figure 11.
39.li (*3.C)
Energy CaUnco for a Particular Cycle of OH Furnace (Top)
and of
-------
A significantly lower value was reported by Dunning, Loeary, and
Thumbower as part of the Westinghouse Energy Utilization Project (Reference 42).
Their analysis determines the furnace efficiency of gas furnace to be 47 percent
based on an hour by hour computer study of the heat losses and gains of a char-
acteristic house. A furnace efficiency of 42 percent was reported for the equi-
valent house heated with an oil furnace. Their analysis takes into account the
heat provided by a variety of other heat sources, such as appliances, occupants,
and the sun, and the heat required to warm to room temperature that outside air
infiltrating to replace air going up the flue.
Similar efficiencies were reported by Kurylko (Reference 43) in a study
of 1260 oil fired home heating plants in the Boston area. He found thermal ef-
ficiences as low as 48 percent, although 15 percent of the oil burners were
found operating close to optimum with efficiencies above 80 percent.
These significantly lower overall efficiencies may be partially ex-
plained by referring back to Figures 9 and 10 which show the typical tempera-
ture rise on the air side. Notice that the fire is extinquished at the peak
temperature rise on the air side. It is at this point the peak ("certified")
efficiency is probably achieved. For the remainder of the cycle the air
blower remains on but the flue gas temperatures and flowrates have dropped.
Perhaps more important and what is not shown on this curve is that the burner
has been firing for several seconds prior to the blower on cycle. This again
means that there is a significant period of time when there is no flow (or
very little flow) on the air side and therefore inefficient heat exchange is
occurring. Of course, some of this heat is stored as heat capacitance in the
furnace structure to be eventually recovered but much also escapes out the
stack under inefficient conditions.
An oversized furnace will in addition accentuate the cycling phenomena.
Although the methods outlined by ASHRAE for determining the heat load in a
structure [see Chapter 21, ASHRAE Handbook of Fundamentals (Reference 34) or
Chapter 2 of Strock, Handbook of Air Conditioning, Heating and Ventilating
(Reference 36) are quite detailed, many residential furnaces are grossly over-
sized to assure a wide margin of safety. It might be possible to design a
modulated furnace that would avoid these severe inefficient transients and con-
trol steady state heat output closely to the required heat demand.
Any study of a modulated furnace must explore whether cycling allowed
use of lower cost materials by avoiding higher steady state temperatures. On
the other hand, the problem associated with thermal fatigue due to cycling may
not be as severe with a modulated system. This area warrants further study.
46
-------
In addition using flue shut off dampers during off cycles to prevent
exfiltration of air through the stack may actually result in greater saving
than reported by Hittman (Reference 10). The argument is made that low effi-
ciency heat exchange would be prevented that would normally allow low tempera-
ture gases to pass out of the furnace. The Save-Fuel Corporation which manu-
factures the Vent-O-Matic damper (see Section 3.5.3) claims savings of 20 to
30 percent of the space heating requirement.
In any case, during the steady state portion of the cycle (if one real-
ly exists), from 20 to 30 percent of the input energy escapes from the stack.
Addition of a heat recovery device or a higher efficiency furnace (steady
state) would not only improve the steady state efficiency but quite likely
the overall efficiency.
3.4 HIGH EFFICIENCY FURNACE AND HEAT RECOVERY DEVICE RESEARCH
During the course of the study portion of this task a number of manu-
facturers or associations were contacted which had conducted or are conducting
studies of high efficiency furnaces or heat recovery devices.* For ^example-,
Chevron Research are presently doing a cost effectiveness evaluation on com-
mercially available heat recovery devices. This study will lead to the de-
velopment of improved devices. However, all this information is proprietary.
Other large manufacturers, such as GE, indicated that they have built or are
designing higher efficiency furnaces (> 90 percent).
Electric Furnace Man (EFM) has developed a hydronic furnace with 89.5
percent efficiency (Reference 44). A recent development is the Heat Transfer
Module developed by AMANA (Reference 44). A solution of ethylene glycol and
water is heated in the "Heat Transfer Module" (HTM) and then passed through
the air conditioning coils to transfer the heat to the room air. The HTM and
furnace is pictured in Figures 12a and i2b. The natural gas fuel burns on a
central cylinder and passes readily through a porous matrix carrying the heat
transfer liquid. One unique feature of this unit is that the gas .is ignited
with spark ignition rather than a pilot flame. In addition a forced draft
Most research, however, has been in the area of heat pumps rather than in im-
provements of conventional systems. The Westinghouse Utilization project
(Reference 42) showed that there was overall cost benefit for heat pumps over
gas and oil system in the majority of the locations studied. Since the sub-
ject of heat pumps, heat pump-solar energy systems, and total residential
energy conservation projects utilizing heat pumps is covered in detail in
other references (Reference 2), no further discussion will be given here.
Similarly, considerable research is being conducted in the academic community
as was indicated in Table 1, particularly in the area of solar energy research.
However, no specific academic programs were found relating to a high efficienT
cy furnace or heat recovery device.
47
-------
Figure 12a. AMANA Electric/Gas Heating Cooling
Unit Using the HTM*
-------
The first major breakthrough in heating technology in years.
The Exclusive
- r <'r / --i r- • Hr1! '•' P
fJLlJsJjU^* _T-J j iA/U
It's only 9" high and 9" in diameter. It's the most
advanced and compact heating system available today.
Here's how it works:
(1) Gas (natural or propane) is pulled from
the gas valve by the combustion blower
into the HTM* Heat Exchanger burner.
The burner is only 4" high x 2" in
diameter.
(2) A spark plug ignites the gas and air
mixture in the burner. No wasteful, both-
ersome pilot light. Wind does not affect
its operation.
(3) A flame probe monitors the burner to
give proof of combustion. If combustion
doesn't take place, the flame probe will
close the gas valve within 15 seconds.
(4) The stainless steel burner provides 9000
tiny flames which produce extremely
hot flue gases.
These gases passing through the por-
ous matrix create high turbulence to
produce rapid heat transfer. Exclusive
porous matrix is made up of thousands
of copper coated steel balls fused to-
gether to perform the function of heat
exchange.
(6) The solution (50% water and 50% eth-
ylene glycol to prevent freezing) carry-
ing tubes embedded in the matrix pick
up the heat and transfer the hot solu-
tion, moving at 4.7 feet per second,
through the HTM* Heat Exchanger.
(7) A limit control monitors the tempera-
ture of the solution. And, if it rises above
design temperatures, it shuts down the
system.
(8) You get 7%-10% more usable heat
than industry standards (depending on
the firing rate) from the gas burned be-
cause of less heat loss through the flue.
(9) The heater keeps the temperature of
the HTM* Heat Exchanger above sur-
rounding temperature at all times, so it
remains dry and untarnished by atmos-
pheric moisture.
Figure 12b. AMANA Heat Transfer Module
-
-------
combustion air fan is used to overcome the pressure drop of the combustion
chamber and heat exchange surfaces. No draft diverter is required. Overall
efficiencies, however, range between 75-89 percent depending on load.
The American Gas Association has been conducting studies for the past
10-15 years on improving heat exchange performance and evaluating new or dif-
ferent ways to heat the home. DeWerth and Smith (Reference 21) studied the
effects of flame aeration, quantity and direction of recirculating air flow,
internal flue baffling and heat exchanger materials of construction on heat
transfer efficiency. Experimental application of the developed optimum heat
transfer conditions produced on 18.5 percent increase in element loading.
Since this data are now about 13 years old, it is quite likely most of the
results have been incorporated into present designs.
DeWerth, Schaab, and Hellstern (Reference 19) studies several new ways
of heating localized areas around the home. Seven experimental units were de-
veloped which operate at an efficiency of 80 percent or more. Many of the
prototype units can be scaled to sizes and capacities of central heating sys-
tems. The following designs were investigated:
• Baseboard Designs
Direct-Fired Tube-In-Tube Baseboard Convector
Liquid Filler Baseboard Heater
U Tube Direct-Fired Baseboard Convector
• Outdoor Installation
High Temperatures, High Velocity - Forced Air Baseboard Heater
• Radiant Types
"Infra-Vector" Heater
Radiant Bathroom Heater
Metallic Radiant Heater
Of particular interest is that three of the designs have "power" ex-
haust systems necessitated by higher pressure drop designs. One of these de-
signs, the high velocity, high temperature forced air baseboard heater, is
shown in Figure 13. It is possible that this design could be scaled to cen-
tral heating system size.
50
-------
1. SINGLE POLE DOUBLE THROW FAN LfMIT CONTROL
2. HIGH TEMPERATURE LIMIT CONTROL
J. HOT AIR FEED TO ROOM
It, DUCT FROM FLUE EXHAUST BLOWER TO OUTSIDE
5. BURNER AND VENTURI
6. PILOT SWITCH
7. PILOT
8. BLEED TUBE FOR VALVE
9. PRESSURE SWITCH - (VALVE CONTROL)
10. PRESSURE REGULATOR
11. 110 VAC GAS VALVE
12. HEAT EXCHANGER
1J. FLUE DUCT TO FLUE EXHAUST BLOWER
1<». INLET AIR SUPPLY OPENING
15. VENT CAP FOR BALANCED FLUE SYSTEM
16. FLUE PRODUCT'S EXHAUST OPENING
17. CIRCULATING AIR BLOWER
18. FLUE EXHAUST BLOWER ..
Figure 13a. The High-Velocity, High-Temperature,
Forced-Air Baseboard Heater System
6 INCH TUBE
5 INCH TUBE
1| INCH TUBE-,
INLET DUCT
DISTRIBUTION
AIR
_WARM AIR DUCT
TO ROOM
EXHAUST DUCT
Figure 13b.
Section View of the Heat
Exchanger and Air Flow
51
-------
In a later AGA study Griffiths and Niedzwiechi (Reference 20) investi-
gated several novel high efficiency concepts for central heating systems.
Figures 14 through 23 show the following schemes considered:
• Ceramic heat exchanger forced air furnace
• Four pulsed combustion furnaces
• Warm air heating panel
• Warm water heating panel
•. Direct force wall panel
• Snorkel-vented dual wall furnace with bypass arrangement
• Forced air furnace with integral blower heat exchanger
All of these furnaces were constructed on an experimental basis and found to
operate with efficiencies of 75-85 percent or higher. Considerable experi-
mental data is reported in Bulletin 101 on each of these designs. To our
knowledge none of these designs has found a commercial marketplace nor has
further research been carried out except for the pulsed combustion concept.
This bulletin also reports the results of an experimental investigation which
increased the heat exchange area of a conventional gas fired central heating
furnace. The draft hood of the furnace was removed and combustion products
were passed through a secondary heat exchanger. An exhaust blower was placed
at the outlet of the secondary heat exchanger to vent the combustion products.
The flue losses were reduced from 22.5 percent to 12 percent with the same
mass flow through the unit. The modified unit was also tested under natural
draft conditions and found to be unstable during the first five minutes of
operation. Steady condensation of water vapor took place during these tests.
The report points out the following precautions if a condensing system is
used:
• Corrosion resistant materials would be required, particularly if
trace amounts sulfur are present in the exhaust gas stream.
• All ducting would have to have watertight joints and seams.
• A forced draft system might be needed.
AGA is continuing to do research on the pulsed combustion concept.
The latest Research and Development Bulletin (Reference 18) of AGA describes
the work under way:
52
-------
III. Evaluation of Potential Home Heating Systems
COLLECTOR
DUCT TO EXHAUST BLOWER
CERAMIC FELT GASKET
CEMENTED EDGE FOR SEAL
VERTICAL PASSAGES
FOR FLUE PRODUCTS
HORIZONTAL AIR PASSAGES
THROUGH HEAT EXCHANGER
CEMENTED EDGE FOR SEAL
CERAMIC FELT GASKET
METAL BURNER JACKET
HOLE FOR SPARK IGNITOR
INSULATING BRICK
CRISS-CROSS CERAMIC
INLET PLATE
GAS AND COMBUSTION
AIR INLET
GAS SUPPLY
Figure 14a. Cross Section of Ceramic Heat Exchanger-
Burner Unit
53
-------
III. Evaluation of Potential Home Heating Systems
-BLOWER MOTOR
r—EXHAUST
\ BLOWER
1 \
-FLUE OUTLET
BURNER
COMBUSTION
CHAMBER
COMBUSTION
AIR INLET
GAS
CONTROLS
Figure 14b. Cross Section of Ceramic Heat Exchanger
Force-Air Furnace
54
-------
SPARK PLUG
TAILPIPE
COMBUSTION CHAMBER
CA) STARTING PHASE
FLAPPERS
CLOSED
EXHAUST
PROD.UCTS
CB) POSITIVE PRESSURE PHASE
CO NEGATIVE PRESSURE PHASE
Figure 15. Schematic Illustration of the Pulse
Combustion Process
55
-------
2 EXHAUST
MUFFLERS
r MUFFLER
COMPARTMENT
FURNACE
EXHAUST
OUTLET
COMBUSTION
AIR INLET
INLET'MUFFLER
WARM AIR
OUTLET
2 - i|8" SECTIONS
FINNED PIPE
25 FINS PER FOOT
EXHAUST EXPAN-
SION CHAMBER -
12" X 12" DIA.
OUTSIDE DIMENSIONS
OF UNIT: 35" WIDE,
26" DEEP AND 76"
HIGH
PULSE COMBUSTION
VALVE ASSEMBLY
INLET EXPAN-
SION CHAMBER
CIRCULATING
AIR BLOWER
CONTROL COMPART-
MENT AND BLOWER
AIR INLET
Figure 16. An Experimental "Finned Tube"
Pulse Combustion Furnace
56
-------
OUTSIDE DIMENSIONS OF UNIT:
2
-------
COMBUSTION
AIR INLET
INLET MUFFLER
INLET EXPANSION
CHAMBER 14 BY 8
BY 8 INCHES
TAILPIPE - 7 FEET
OF 1-1/2 INCH PIPE
FLUE EXHAUST
FUEL INLET
GAS RESERVOIR
COMBUSTION CHAMBER
*1-1NCH DIAMETER BY
OR 12 INCHES LONG
EXHAUST EXPANSION
CHAMBER 12-INCH
DIAMETER BY 12
INCHES LONG
CIRCULATING
AIR BLOWER
OUTSIDE DIMENSIONS OF UNIT:
18 INCHF.S WIDE, 22 INCHES
DEEP AND 60 INCHES HIGH
Figure 18. An Experimental, Hi-Boy Pulse
Combustion Furnace
58
-------
2 BY
3/'t" THICK
FIRRING STRIPS
INSULATION
ALUMINUM FACING
SHEET METAL
WARM AIR PANEL
. WARM AIR
DISTRIBUTION
PLENUM
\ \\ WARM AIR
\\INLET OPENINGS
INTO PANEL
WARM AIR
DISCHARGE
OPENINGS IN
PANEL
Figure 19. An Experimental, Warm Air
Heating Panel System
59
-------
' l'l '
1 h r
ll III 1
11
WATER
OUTLET
GAS BURNER
FORCED DRAFT BLOWER
1 INCH DIAMETER BY 56-INCH
LONG COMBUSTION CHAMBER TUBE
1/2 INCH THICK
INSULATION
*»-INCH DIAMETER BY
5^-INCH LONG "WATER
JACKET
WATER INLET
3-INCH BY 1 INCH
BELL REDUCER
GAS PILOT
GAS
Figure 20. An Experimental Heat Exchanger for a
Warm Water Heating Panel Application
60
-------
VERTICAL
STIi
BURNER
A
BALANCED FLUE
oZ"_
28
76"
28"
^
A-L.
2"
INLET AIR
CHANNEL
SECTION A-A
BURNER
AIR CHANNEL OPEN
AT TOP AND BOTTOM
FRONT PANEL
107 - NO. 41 PORTS SPACED
C TO C-ALONG TOP BURNER
GAS
f U.
! --"^n/iJ
DISTRIBUTION
TUBE '•
.NO. 64 DMS
-• GAS ORIFICE
AND PRIMARY ' SECTION B-B
.AIR OPENING
EIGHT 1/8" D HOLES IN
BOTTOM OF DISTRIBUTION
TUBE 3" C TO C
Figure 21, Experimental Direct-Fired Wall Panel
61
-------
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HOT AIR
"OUTLET
3 DUCT SECTION HEAT EXCHANGER PANELS
5-INCH DIAMETER
VENT
10-INCH
DIAMETER
BLOWER
FILTER AND
AIR INLET
COMBUSTION J
AIR INLET
MANIFOLD,
CONTROLS -1
AND BURNER
BLOWER DRIVE MOTOR
CIRCULATING AIR FLOW
PASSAGES CONTAINING COMBUSTION
PRODUCTS
NOTE: WIDTH OF UNIT 19 INCHES
Figure 23. Forced-Air Furnace with Integral
Blower-Heat Exchanger
63
-------
The burner is immersed in a small nonpressurized
water tank, transferring most of the heat input
through its walls to the water. The burner's
combustion products exit under water in the up-
per part of the tank, using pressures developed
by the pulse combustion process to vent these
gases. The heated water is then circulated
through a finned water-to-air heat exchanger to
heat circulating room air. Flue gas temperatures
of 100°F with C02 concentrations of 9 to 10 per-
cent are achieved with this arrangement, provid-
ing efficiencies of 90 to 95 percent, based on
flue losses. At the same time, bubbling flue gases
through the water effectively muffles noise of
operation at the exhaust to a very low level. Fur-
ther work is under way to minimize operating noise
at the inlet and consideration is being given to
air heat exchanger design, materials of construc-
tion and arrangements of components to provide
compactness.
The latest developments on this concept are considered to be proprie-
tary, however, and no recent reports have been published.
The only other research efforts on heat recovery devices found in the
literature were another AGA study by Potter and Wail (Reference 22) and an NBS
document by Garrivier on the Use of Air to Air Heat Exchange Systems (Reference
46). These papers deal primarily with either large, higher temperature recu-
perator systems or with the recovery of ventilated air from commercial
building. Many of these heat recovery systems for commercial buildings are
currently available on the market.
3.5 HEAT RECOVERY DEVICES COMMERCIALLY AVAILABLE
Discussions with furnace manufacture personnel at the Center for Build-
ing Technology at NBS, review of the ASHRAE Journal and other HVAC journals,
as well as such popular publications as Popular Mechanics and Popular Science,
and follow up of other leads have revealed only two devices presently on the
market for residential application: a heat pipe device marketed by Isother-
mics of Augusta, New Jersey and a flue gas to air heat exchanger manufactured by
Dolin of Brooklyn, New York. Descriptive literature on each of these devices
will be found in the appendix. The paragraphs below provide brief descriptions.
3.5.1 Isothermics Air-O-Space Heater
The Isothermics Air-0 Space Heater utilizes 3-5 finned heat pipes pro-
jecting into the flue (see Figure 24). A separate 100 CFM blower delivers air
across the opposite end of the heat pipe to recover the energy. Figure 24
also shows the potential heat recovery as a function of stack temperature.
64
-------
'
HOT
AIR
— FURNACE
Space heater uses series of heat pipes to
extract heat from hot flue gases exhausted
from oil-fired home furnace. Recovered heat
can be used to heat the basement or directed
to the supply duct. Fan blows cool air over
condenser end of heat pipes which are
isolated from ends in flue by a metal barrier.
Fan plugs into 115-v a-c outlet and is
controlled by a thermostat in supply duct.
Heat output can be adjusted by moving pipes
in or out of flue. Air-O-Space Heaters can
recover from 5000 to 15.000btuh, depending
on number of pipes in unit (3, 4 or 5), and
stack temperature. Unit weighs 15 Ib and
installs in standard 6-in. tee in about 15 mm.
Figure 24. Isothermics - Air-O-Space Heater
-------
The normal operating range is for flues in the 500°F to 800°F range. In fact
Isothermics does not recommend using the unit if the flue is below 500°F for
two reasons:
1. The potential heat recovered is below 5000-7500 Btu/hr, or less
than 5 to 7.5 percent improvement in efficiency for 100,000 Btu/hr
furnace.
2. The exit gas temperatures downstream of the unit will become low
enough to cause condensation.
They also recommend that the unit be cleaned periodically and removed
during the nonheating season. The device sells for around $100 plus installa-
tion.
Isothermics indicated they have other domestic units in the prototype
stage, but all information is proprietary.
3.5.2 Dolin Metal Products - Heat Reclaimer
The Dolin Heat Reclaimer is a simple flue gas to air heat exchanger
made up of 52 3/8" base steel tubes on a 5/8" triangular pitch (see Figure 25).
Cooling air provided by a separate blower flows through the tubes while flue
gases are directed over the tubes. Unfortunately, wide gaps on either side of
the heat exchanger surface on the flue gas side allow nearly half the flow to
bypass the unit. This is regarded as a "safety" feature in case the tube bun-
dle becomes plugged. Dolin claims 19,800 Btu/hr heat recovery at a flue tem-
perature of 800°F, although they have no test data to substantiate this claim.
A simple analysis reveals a more likely figure of 5300 Btu/hr at 800°F. Figure
26 shows the more detailed results of this analysis which may be found in the
appendix. As in the case of the Isothermic Unit, Dolin stipulates that the
unit should not be used with flue temperature below 500°F and that the unit
should be inspected and cleaned periodically. This unit sells for $130 plus
installation and optional duct and register kit.
3.5.3 Other Manufacturers and Devices
Several other manufacturers were contacted who indicated they manufac-
tured heat recovery devices. Table 13 gives the companies contact and the
type of equipment they manufacture. As can be seen from the table, none
offers equipment in the residential furnace size range.
66
-------
Heating engineers have designed a
simple, relatively inexpensive unit that
reclaims the wasted heat from oil and
coal furnaces that is normally lost
up the chimney. It's called . . .
The Dolin
DOLIN HEAT-RECLAIMER
Suggested Retail Price: $130.00
(Installation not incl. See your dealer.)
1. Motor and Blower
2. Flue Pipe Adapter (Specify
flue pipe diameter: 5" to 10".)
3. Reclaimer Housing
4. Reclaimer Core
OPTIONAL DUCT AND REGISTER KIT
Suggested Retail Price: $15.00
5. Transition Piece
6. Register Box
7. Register Grill
8. 4" Duct (supplied and installed by
local dealer.)
Figure 25. Dolin-Heat Reclaimer
-------
6000
5000
0)
or
a\
oo
4000
3000
Furnace Size:
Excess Air:
Cooling Air Temp:
Cooling Air Flow:
100,000 Btu/hr
60% (Oil Fired)
60°F
61 scfm*
500
600 700
Flue Inlet Temp (°F)
800
See attached curve of resulting operating point of Blower
Figure 26. Dolin Heat Reclaimer Performance
-------
TABLE 13
HEAT RECOVERY DEVICE MANUFACTURERS
Company
Product
Wing Co., Division of Aero
Flow Dynamics, Inc.
Linden, New Jersey
Hughes Tool Co.
Torrance, California
Heat Recovery Corp.
Kearny, New Jersey
Heat Pipe Corp. of America
Whippany, New Jersey
Industrial Air, Inc.
Ameilia, Ohio
Q-Dot Corp.
Dallas, Texas
Rotary air to air heat exchangers - applied
to ventilated air
Manufactures line of heat pipe to be applied
by others.
Manufactures large heat exchangers for
industrial and commercial applications.
Building prototype unit; no product yet.
Referred to Q-Dot.
Manufacturers large heat exchangers for
industrial and commercial applications.
Heat pipe devices for commercial buildings;
heat recovery of ventilated air.
69
-------
In England, a common method of heat recovery uses concentric flue and
combustion air supply piping. In this country, the combustion air supply is
normally taken from the house air and/or from vents below the house. No fur-
ther information has been obtained to date on the concentric flue design ap-
proach. Section 4.1.5 discusses this general scheme.
Two manufacturers of automatic flue dampers were contacted for informa-
tion.
Save-Fuel Corporation
The Vent-0-Matic Device manufactured by the Save Fuel Corporation
claims to save between 20 to 30 percent of the space heating requirements.
The vent is automatically opened electrically prior to the burner ignition and
interlocked with the heating applicance gas valve to prevent ignition if the
vent is not open. The unit was initially approved by the AGA and the Canadian
Gas Association as well as by numerous city public works departments.
However, AGA recently withdrew their approval for application to old
furnace systems and the matter is under study by the Federal Power Commission,
Federal Trade Commission and Senate Antitrust Committee.
It has not been applied and tested on oil fired units however. The in-
stalled cost of this unit is around $100. A bulletin on the device will be
found in the appendix.
Werner Diermayer
Werner Diermayer offers a thermally actuated vent damper for about
$7-$15 in Europe. This unit utilizes bimetal quadrants as the closure plates.
AGA approval has not been granted, although the unit has been used for over
40 years in Europe. A bulletin describing the device will be found in the
appendix.
i
I
70
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SECTION 4
IDENTIFICATION OF ALTERNATE HEAT RECOVERY DESIGNS
Section 3.5 above identified the current state of the art in furnace
and heat recovery design. Earlier sections indicate that a potential of 20 to
35 percent of the input energy is available for recovery. Depending on the
flue gas temperature, 30 to 50 percent of this energy is from the latent heat
of vaporization of the water in the products of combustion. Thus to realize
a significant heat recovery, particularly with the higher efficiency, lower
exhaust temperature furnaces that are found in a large number of homes, a con-
densing system will be required.
Because of the different engineering problems involved, it is useful to
consider designs in two separate categories:
• Retrofit schemes for existing furnaces
• New furnace design
Each of these general approaches will be discussed in the following
sections.
4.1 RETROFIT SCHEMES
In a retrofit approach the furnace may be regarded either as a black
box with a hot flue gas stream exiting from the unit or a system subject to
internal modifications. In the first approach we concentrate on add-on de-
vices, outside of the original envelope of the furnace, for exchanging heat
between the exit flue gas stream and any of several other streams of interest,
such as the intake air. Section 4.1.1 presents various alternatives in this
general class. The second general approach, discussed briefly in Section
4.1.3, contemplates modificaitons much as heat transfer improvements, within
the original furnace envelope.
4.1.1 Black Box Approach
4.1.1.1 General Discussion
In this approach a hot flue gas stream is available to exchange heat
with some other medium. The other medium may be one or more of the following:
71
-------
1. Combustion air
2. Fuel
3. Recirculating house air/water exiting from furnace
4. Recirculating house air/water returning to the furnace
5. Independent air/water stream
6. An intermediary fluid or solid which eventually exchanges heat with
one of the other mediums (trade jargon denotes systems of this type
as "runaround" systems)
Alternatively, one might also consider converting that energy directly
into work or electrical energy. The latter two ideas will be further discus-
sed in Section 4.3, NOVEL APPROACHES. The Isothermics device utilizes Methods
5 and 6 by using the fluid in the heat pipe to exchange heat with an indepen-
dent air supply. The Dolin device uses Method 5 to exchange an independent
air supply directly with the flue.
The advantages and disadvantages of each of these approaches are tabu-
lated and ranked subjectively according to probability of success in Table 14.
Although the Method 6 "runaround" circuit shows a fairly high potential, the
cost is probably greater, except for the heat pipe approach, than for schemes
3, 4, and 5.
Rotating heat capacitance systems represent another offshoot of Method
6. The rotary metal or ceramic wheel used on gas turbine recuperators or ven-
tilation ducts of commercial buildings is an example of this approach. Rotat-
ing wheels that allow leakage between streams could not be allowed with a
flue-gas-to-house-air system. However, it may be possible to mechanically ro-
tate a solid between streams with adequate sealing. The chief disadvantages
with solid rotation are as follows:
• Mechanical drive system reliability and noise
• Sealing, leakage, and conveyor problems
• Limitation on heat uptake rate by transient conduction effects
Since the probability of success of this scheme seems fairly remote and
since the heat pipe represents an inexpensive and simpler solution, this ap-
proach was not further explored.
72
-------
TABLE 14
"BLACK BOX" HEAT EXCHANGER SCHEMES
Scheme
Number
1
2
3 A
W
4 A
W
5
Exchange Flue
Heat With
Combustion Air
Fuel
Hot Air from furnace
Hot Water from furnace
Cold Air to furnace
Cold Water to furnace
Independent air/water
stream
Advantages
• Equal mass flow rates
• Room air (low temperature)
available for heat exchange
t Low temperature duct work
• Compact heat exchanger
• Easy retrofit
• Flue stream and air stream
are parallel and adjacent
in up flow design
• Possibly can get by with-
out auxiliary air fan
• Simple piping
• Does not require auxiliary
pump
• Potential for condensing
heat exchange
t May not require auxiliary
fan
• Simple piping
• Potential for condensing
heat exchange
• Does not require auxiliary
pump
• No change to main air
ducting
• Can choose air/water flow
for optimum heat exchanger
design
• Does not affect main air/
water flow rates
• Probably least expensive
scheme
• Can run duct to spare room,
garage, basement, etc. or
back into main air stream
if pressures compatible
• Potential for condensing
heat exchange
Disadvantages
• Preheated combustion air
may produce excessive
furnace metal tempera-
tures
• Require extensive duct
work
• May not be compatible
with a naturally aspir-
ated gas burner or oil
burner
• Heat capacity of oil or
gas is fraction of avail-
able within temperature
restrictions
• Potential for heat reco-
very limited to noncon-
densing case due to ~ 140
air temperature
• Will decrease main air
flow rate
• Potential for heat recov-
ery limited to noncondens-
ing case due to 180 water
temperature
• May decrease total water
flow rate
t Required extensive duct
work reventing
• May decrease main air flow
rate
• May decrease main water
flow
• May not be compatible with
a hydronic system
• Requires auxiliary fan or
pump
• In some case would require
extensive separate duct
work or piping
Rank*
5
6
4
3
1
73
-------
TABLE 14 (Concluded)
"BLACK BOX" HEAT EXCHANGER SCHEMES
Scheme
Number
6
Exchange Flue
Heat With
Intermediary Fluid
("Runaround Circuit")
Advantages
• Least possibility for leakage of
gas/air streams
• Simple manifolding - can run
streams in parallel
• Ideal for heat pipe
• Potential for heat sink remote
from heat source
Disadvantages
• Except for heat
pipe, requires au-
xiliary "runaround
circuit" and equip-
ment (pump, valves
piping, etc. )
Rank*
2
*1 = best
6 = worst
74
-------
A more elaborate version of Scheme 5 (or Scheme 6) would have a heat
pipe unit or heat exchanger transfer heat to a central energy recovery water
loop to store energy in a hot water system. All energy using appliances
should be tied into this scheme to achieve best results. This scheme, while
it may offer some advantages, seems unlikely to contribute an economical
retrofit scheme.
Since the usual versions of Schemes 5 and 6 are already represented
on the marketplace, no further detailed analyses were done on these. However,
the potential for improving on these devices still exists. Table 15 lists
some possibilities.
In general the disadvantages of Method 1 outweigh the advantages re-
sulting in a fairly low ranking. However, as was mentioned earlier the
British commonly use this system in the form of concentric inlet and outlet
ducts for the flue gas and combustion air. Furnaces are designed to accommo-
date the preheated combustion air and higher flame temperatures.
Scheme 2 can be dismissed because the heat capacity of the fuel within
the temperature limitation of the flue gas is a small fraction of the poten-
tial heat recoverable.
4.1.1.2 Design Problem Areas
Problems common to all retrofit designs will be discussed in more de-
tail in the following paragraphs:
Pressure Drop
It can be shown by conventional heat exchanger design techniques that
to increase the system efficiency by only 7 percent using existing furnace
heat surface types (heat transfer coefficient approximately 2.7 Btu/hr-ft2°F),
thereby incurring minimum pressure drop, would require nearly double the sur-
face area. A preferable solution uses more compact heat exchange surface
(high surface to volume ratios), higher heat transfer coefficients and con-
sequently higher pressure drops. Tables 8-10 in Section 3 indicate that the
available pressure exhausting the products of combustion is quite limited, on
the order of 0.05-0.2 inches H-O. Thus it seems quite likely that to decrease
the flue temperature below 500°F an induced draft fan will be required. The
feasibility of this with a naturally aspirated gas fired burner has been
shown by DeWerth, et al. (Reference 19) in a novel wall furnace (see Figure
13 in Section 3).
75
-------
TABLE 15
IMPROVEMENTS TO EXISTING DEVICES
Scheme
Number
5
6
Present
Manufacturer
Dolin
Isothermics
Improvement
• Close off bypass area
• Use fin tubes
• Increase heat transfer
area to achieve con-
densing heat exchanger
t Use plate-fin heat ex-
changer
• Increase heat transfer
area to achieve con-
densing heat exchanger
Problems
• Satisfying local city
safety codes
• Provision for condensate
• Change ducting materials
to avoid corrosion
problems
• May require induced draft
fan once the bouyancy is
reduced and pressure drop
increased
• Provision for condensate
• Change ducting materials
to avoid corrosion
problems
• May require induced draft
fan once the bouyancy is
reduced and pressure drop
increased
76
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Condensate
If temperatures anywhere in the system (including surface temperatures)
get below the dewpoint (approximately 123°F, depending on fuel, excess air and
relative humidity (see Figure 27), condensation will begin. If the flue is
cooled to 100°F approximately 2 to 2-1/2 qts/hr will be condensed for natural
gas combustion with 60 percent excess air. Provision must then be made for col-
lecting and draining off this water. Careful installation of the device is re-
quired as well to prevent condensate from flowing back into the furnace.
Corrosion
As the dewpoint is reached on any metal surface and condensate begins
to flow, the potential of corrosion exists due to the sulfur in the fuel.
The problem will no doubt be more severe for oil and coal fired furnaces than
for gas fired. Most furnaces are manufactured from carbon steel and the flues
from galvanized steel or aluminized steel. The choice of materials for the
heat exchange surface and ducting will depend on the temperature level and
whether there is a condensing condition. It may be possible to use different
materials in different temperature regimes. Table 16 lists some potential
materials of construction, maximum temperature, relative cost, resistance,
thermal conductivity (important for finned surfaces), and potential application.
It should also be kept in mind that once the bulk exhaust temperature gets be-
low 300°F, the probability of condensation on cold metal surfaces is fairly
high; therefore, any heat recovery device applied to flue temperatures below
500°F will probably require a change of ducting material.
Thermal Stress and Cycling
Thermal stresses and thermal cycling are common problems with all fur-
nace components which must be taken into account in the design. Temperature
gradients, particularly in cross flow heat exchangers, can easily produce des-
tructive thermal stress in an improper design. In addition, many commercial
systems suffer from failures due to fatigue cracking causes by cyclic stresses.
Overcoming these problems usually requires extensive experience and/or rather
sophisticated analysis. AGA has a program devoted to studying the problem of
cycling fatigue as this remains the principle failure mode of the main furnace
heat exchanger.
77
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PER CENT EXCESS AIR
S g S 5 S
.04
.08 ~!iz I B I iSp I 3^ I 53 I 35T
WEIGHT RATIO H2/(s-t-C) FOR 'SOLID AND LIQUID' FUELS
.40
400
600 ] 1200 ] 1600 1 2000 | 2400 ( 2800
I BTU PER CUBIC FOOT FOR GASEOUS FUELS
3200
3600
4000
PER CENT[ OXYGEN TOTAL [DRY FLUE PRODUCTS) |
20
10
20 30 40 50 60 70 80
PER CENT DRY AIR IN TOTAL DRY FLUE PRODUCTS
90
100
Figure 27. Theoretical Dew Points of the Combustion Products of Industrial
Fuels
78
-------
TABLE 16
POTENTIAL MATERIALS OF CONSTRUCTION
Material
Carbon Steel
Aluminized Steel
Copper
Aluminum
(3003)
Stainless Steel
(409)
Stainless Steel
(301)
Galvanized Steel
Porcelain Coated Steel
Ceramic Plasma Sprayed
Steel
Plastics
Maximum
Temperature
Range
(°F)
800-900
1180
500
400
1100
1470
550
1100
1100
250
Corrosion
Resistance
Poor
Fair
Fair
Fair
Excellent
Excellent
Fair to Poor
Excellent
Excellent
Excellent
Thermal
Conductivity
Btu/hr-ft°F
26
-26
220
116
8.0
9.4
26
26
26
.05-. 2
Cost
$/#
.33-. 42
.9-1.0
.74
1.05
1.15-1.20
.24
Potential Application
Furnace H.E. surface
Duct - noncondensing
H.E. - noncondensing
Low Temperature H.E.
Low temperature but noncon-
densing H.E. ducts
All parts
All parts
Ducts - noncondensing
Ducts - condensing possibly
H.E.
Ducts - condensing possibly
H.E., poor fabricability
Ducts - low temperature
H.E. - low temperature
-J
ID
-------
Potential Heat Recovery
Figure 28 shows the potential heat recovery as a function of flue tem-
perature upstream and downstream of the device, for a 100,000 Btu/hr furnace
operating on natural gas at 60 percent excess air. From this curve it can
be seen that with a low upstream flue gas temperature one must go into the
condensing regime to achieve significant percentage heat recovery. If the
furance is fairly inefficient and the upstream flue temperatures are high
(800°F), significant recovery can be made in the noncondensing regime.
4.1.1.3 Conclusions
All the retrofit external modification schemes share some common pro-
blems summarized briefly in Section 4.1.1.2. In addition, each of the
methods has particular difficulties, as discussed in Section 4.1.1.1 and sum-
marized in Table 14. Scheme 2 is definitely not feasible. Scheme 1, although
sound in concept, does not appear practical as a retrofit scheme for the geo-
metries of common U.S. furnaces. Schemes 3, 4, and 5 appear to survive this
first examination as candidates for retrofit schemes; more detailed analyses
of these concepts will be described in Section 5.
4.1.2 Internal Modifications
It may be possible to design a device such as additional surface which
would be inserted as a retrofit unit into a furnace heat exchanger to improve
the heat transfer performance. This would have to be done within the pressure
limitations of the burners, unless an induced draft fan could be added. Only
sensible heat could be recovered since condensation within an existing furnace
could not be tolerated. Care would also have to be taken so that furnace wall
temperatures would not become excessive. Access to the heat exchanger surface
would be a problem in many cases and installation costs would usually be high.
For these reasons this avenue was not further pursued at this time.
80
-------
-D
01
01
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o
o
O)
cc
-------
4.2 NEW FURNACE DESIGNS
Two general clarifications of new furnace design approaches can be made.
• Increase Heat Transfer Surface
• Novel Approaches
These are treated separately in the subsections below.
4.2.1 Increased Heat Transfer Surface
As pointed out in the previous section, to increase the efficiency of
the furnace using the existing heat transfer surface configuration would re-
quire excessive volumne. In addition, to increase the efficiency beyond what
is currently being achieved, 80 percent, will require provision for condensa-
tion in the stack or for a full condensing furnace. The latter approach seems
to be the most advantageous. To achieve within a reasonable volume the heat
transfer surface required for a condensing heat exchanger will probably re-
quire a so-called "compact" heat exchanger with associated higher pressure
drops. Therefore, either a "power burner" (forced draft) or an induced draft
fan will be required.
We see no serious impediments to the design of such a furnace. Careful
consideration will have to be given to materials, as mentioned in the previous
section, as well as to cost. Since several large furnace manufacturers indi-
cated they had such designs in the prototype stage, no further analysis was
performed on the concept at this time.
4.2.2 Novel Approaches
Several novel designs have been identified as having potential. They
include the AGA pulsed combustion concept, the ceramic honeycomb and heat
exchanger, a catalytic central house heater, a submerged combustion heater,
and the AMANA heat transfer module approach. The first and last of these were
discussed in Section 3.4. The first, the pulsed combustion development, is
just now being costed by AGA and leading manufacturers. No data are yet
available on this unit. The last is a commercially available system.
A number of other novel ideas as well as the catalytic and submerged
combustion concepts will be discussed in the following subsections.
82
-------
4.2.2.1 Catalytic Combustion
The potential for low emissions and high heat transfer in catalytic
unit rates (References 47, 48) suggest the possibility of applying the concept
to residential heating systems. Several investigations have in fact pursued
this possibility in various forms. The so-called "surface infra-red panels",
in which fuel and air burn on the surface of a porous refractory panel, are
used to supply local heat in several space heating applications such as semi-
outdoor restaurant terraces. The similar catalytic "tent heater" provides
another example of local space heating. The application of such devices to
space heating when burning a hydrocarbon fuel is limited by CO and hydrocarbon
emissions; safety requires adequate venting. Proposed schemes involving hy-
drogen as a fuel do not have stringent venting requirements and have many at-
tractive design possibilities.
In a central heating concept, surface or catalytic combustion is of
chief interest because it may provide a very low NOX combustion unit. Ref-
erence 48 surveyed the current research and development scene and explored
several potential applications, all of which promised low NOX performance.
Several experimental systems have demonstrated excellent combustion and
emission characteristics.
Because surface combustion allows high combustion rates per unit area,
proper design incorporating this concept can reduce equipment size over
that of conventional equipment, and often can achieve dramatically lowered
costs. In addition, if the system is designed to have low mass, the heat out-
put of a surface combustion unit can be modulated with great exactness and
speed. Section 3.3.5 discusses the possible benefits of a modulation or "turn
down" capability.
The small size and high heat transfer rate capability of a surface
combustion unit may make it unsuitable for use with warm air heating because
it typically is difficult to provide a high enough heat transfer coefficient
on the air side to accept the high heat fluxes without forcing heat exchange
wall temperatures too high. The approach should be much better suited to a
water scheme. Table 17 summarizes some of the other potential disadvantages
of the surface combustion approach, and some of the outstanding question areas.
Despite the possible disadvantages and the question areas, surface com-
bustion deserves careful study for house heating application. The subject was
not pursued, however, under this program because EPA is currently sponsoring a
separate feasibility review of surface combustion applied to home heating, in-
dustrial furnaces, and similar applications, following up the critical survey
83
-------
TABLE 17
ASPECTS OF CATALYTIC OR SURFACE COMBUSTION FOR CENTRAL UNITS
Probable Advantages
Possible Disadvantages
Question Areas
1. Clean combustion: low
particulate, low
hydrocarbon, low NO
2. Compact heat transfer
area; implied low cost
3. Modulation capability
if properly designed
1. May not be suitable for
direct transfer to air
2. Unless carefully de-
designed for low mass,
will not be suitable
for short "on" periods
and cannot be modulated
3. Preferred low tempera-
ture operation requires
a catalyst, with associ-
ated problems of cost,
lifetime, and maintenance
4. Cold starts are difficult
Most experiments to
date show higher
hydrocarbon emissions
than desired
Design problems for
liquid fuels are
difficult and need
further study
84
-------
of Reference 48. Should this feasibility study indicate definite potential
in the home heating area, a detailed design and cost analysis task is
recommended.
4.2.2.2 Submerged Combustion
High heat transfer rates and the potential for emission prevention sug-
gest that a submerged combustion might be a feasible scheme for a high effi-
ciency low emission furnace. In fact, the AGA pulsed combustion furnace is
just such a device. However, it is not clear that the submerged combustion
concept can be applied to distillate oil burners and conventional powered gas
burners as well as this novel gas burner. Applications of submerged combustion
are known in the petrochemical industry for combustion of "waste" fuels where
scrubbing of the exhaust products is required. Table 18 lists some of the ad-
vantages and disadvantages of this approach. The problems of light off and
stable combustion are probably the most severe. Figure 29 shows one possible
solution, placing the burner above the water but forcing the products of com-
bustion through the water. The upper part of this immersion tube may have to
be refractory or ceramic lined. Continuous water treatment is also required
to avoid acid conditions in the tank over a period of time. The burner will
be required to develop several inches of water pressure to overcome the im-
mersion depth. As with the catalytic combustion system, there could be a
conflict between the heat capacity and the cyclic nature of home furnaces.
Unless heat output rate can be modulated to match the load, the time response
of this approach may be inadequately slow. Further studies are required to
size the tank, determine the optimum size and type of heat transfer surface
burner configuration, and to determine the dynamic response of the system.
Many of the answers will only be attainable through development of an experi-
mental prototype model.
4.2.2.3 Thermoelectric Device
It is possible to convert the flue gas thermal energy directly into
electrical energy. Thermopiles have been applied to similar problems for a
number of years. The problems associated with this concept are noted below:
• Very low conversion efficiency at low temperatures
• No common home use for the power developed
• High cost; expensive material
For these reasons this concept was not further studied.
85
-------
TABLE 18
SUBMERGED COMBUSTION
Water/Air IN _
To Vent
Water/Air
to Rooms
Gas/Oil
Advantages
Disadvantages
Clean stack gases
• High heat transfer
rates
• Possibility of
direct exchange
with circulating
water
Potential start up
problems
Corrosion and water
treatement problems
High pressure drop,
particulary for gas
Unstable combustion
Possibly expensive
Heat capacitance problems
86
-------
rueu
IT
FLUE.
1t)
Figure 29. Burner Arrangement - Submerged Combustion
-------
4.2.2.4 Other Concepts
Most other concepts for improvements in ventilation heating systems
demand much more elaborate changes and in fact impact the entire energy man-
agement of the building. These were outside the scope of this program, but
deserve (and are receiving) careful study as evergy conservation becomes
more and more important:
• Heat pumping systems, with utilization of main power unit waste heat
• Total energy systems, for single family units, for large buildings,
and for building complexes or residential districts; various main
power units
• Solar-assisted systems of all types
88
-------
SECTION 5
DETAILED ANALYSIS OF RETROFIT SCHEMES
One of the prime objectives of the current study was to conduct a de-
tailed design and cost examination of retrofit flue gas energy recovery units.
These seemed to offer reasonably attractive promise, particularly in the face
of fuel shortages and increased fuel prices. In addition, various and scat-
tered commercial ventures to produce and market very simple versions for such
units with limited goals suggested that the general concept is sound and
competitive.
Section 4.1.1 above reviewed the alternative approaches to flue gas
recovery and identified two general approaches to flue gas energy as most
promising:
• Direct exchange with air/water exiting from the furnace (Scheme 3
of Section 4.1.1)
• Direct exchange with air/water entering the furnace (Scheme 4 of
Section 4.1.1)
These schemes are to be considered for gas and oil fired burners over
a variety of temperature conditions (or furnace inefficiencies) and for air
and water systems. In addition we will consider a noncondensing and a conden-
sing heat exchanger in each case.
Details of the four potential schemes to be analyzed are given in
Table 19, which includes the potential heat recovery rate, the therms saved
per year and potential savings for typical West Coast and East Coast cities.
In this table we follow the numbering system of Section 4.1.1, and
append an A or W to indicate air or water respectively as the heated fluid.
Case 3A represents an approach of exchanging heat with the exit air from the
furnace. This is ideal because a larger number of these are parallel upflow
enabling a simple heat exchanger to be placed at the air outlet side in a
crossflow arrangement. This approach is represented by Case No. 1 and is
limited to a noncondensing heat exchanger because the exit air to be heated
is already higher than the flue gas dewpoint. Scheme 3W represents the same
approach with water as a working fluid. This scheme is marginal since it has
the lowest potential in total energy savings.
89
-------
TABLE 19
POTENTIAL SCHEMES TO BE ANALYZED
Sch
No.
3A
2
4A,C
4A,N
3W
4W
4W,N
Fuel
Gas
Oil
Gas
Oil
Gas
Oil
Gas
Oil
Heated
Medium
Air
Air
Air
Air
H20
H20
H20
H20
Forced or
Natural
Draft
Burner
N
F
N
F
N
F
N
F
Exit
Flue
Temp.
300-
500
500-
800
300-
500
500-
800
300-
500
500-
800
300-
500
500-
800
Heated
Medium
Temp.
140
140
70
70
180
180
70
Scheme
Exchange
flue gas
heat with
exit air
from exis-
ting
furnace
Exchange
flue gas
heat with
furnace
inlet air
Exchange
flue gas
heat with
boiler
outlet
water
Exchange
flue gas
heat with
return
water or
fresh feed
water
Condensing
Heat
Exchange
No
Yes
No
No
Yes
No
Potential*
Heat
Recovery
BTU/Hr
4223-
17419
134937
27797
6000-
19000
3167-
16364
13493-
27797
6000-
19000
Therms/
Year**
Saved
44-
181
140-
289
62-
198
33-
170
140-
289
62-
198
~ $ Savings***
Year
SF
5-20
15-32
7-22
4-19
15-32
7-22
$ Saving/ Year****
Mass.
10/40
30-64
14-44
8-38
30-64
14-44
*
Based on 100,000 BTU/Hr heat input to the furnace; 60% excess air and 85% efficient heat retrofit heat exchanger.
Based on nominal 1040 therms/year normal for heating.
***
Based on $.1 I/therm San Francisco Bay Area cost.
***
Based on $.22/therm for oil.
-------
Cases 3 and 4 allow a choice between noncondensing and condensing ap-
proaches. The noncondensing approach, in which the flue gas is cooled only to
200°F - 250°F to prevent condensation in the flue, is reasonably attractive
for the most inefficient furnaces, i.e., those with exhaust temperatures of
500°F - 800°F; however, Table 20 shows only condensing approaches to Case 4
because noncondensing schemes are already being calculated commercially, ap-
parently with indifferent success.
To achieve a relatively compact arrangement, plate fin and fin tube de-
signs as shown in Figures 30a and 30b were considered; both designs were con-
sidered to see if one held an economic advantage over the other.
Hand calculations proved to be time consuming in evaluating different
passage heights, shapes and overall dimensions. Therefore a simple computer
program "PERF" which utilizes the heat exchanger performance calculation tech-
nique of Kays and London (Reference 49) was written. Given the input informa-
tion listed in Column A of Table 20, the program calculates the performance
as listed in Column B. A listing of this program may be found in the appendix.
It will be noted that the code does not perform a final design choice
but simply runs out a series of designs from which a design may be selected,
by interpolation if necessary, to achieve a specified performance.
For a condensing type heat exchanger it was necessary to use the Log
Mean Temperature Difference (LMTD) technique in conjunction with an approach
detailed by McAdams (Reference 50, pages 355-356) to determine the heat trans-
fer of condensing vapors in a noncondensable gas. Details of this technique
can also be found in the appendix.
Note that the determination of heat exchanger size require simultaneous
solution of heat transfer and pressure drop requirements for the hot and cold
streams. Since the open area and path length, the factors which determine
heat transfer and pressure drop, for one side are a function of the opposite
side, the sizing procedure is often a tedious iterative procedure, even with
the aid of the PERF code. The fact that the air flowrate is approximately 40
times the flue gas flowrate for Schemes 3A and 4A compounds the basic problem.
The design procedure for Scheme 5A is somewhat simplified since the cooling air
flowrate can be an independent variable.
A typical blower performance curve is shown in Figure 31. Assume that a
typical operating point will be 1150 CFM and 0.4 inch HO, as shown in Figure
30. Increases in the system pressure drop of 0.1 and 0.2 inch HO will cause
the flow to drop to 1090 CFM and 1025 CFM, respectively, which should not af-
fect the overall performance of the main furnace. Therefore, if we limit the
pressure drop to tenths of inches of water we should not cause a serious de-
terioration in the furnace performance.
91
-------
(L C L L
-*>*&>**'
LZTT* 7^ /^^
4&W&77V
S
Figure 30. Compact Heat Exchanger Designs
-------
TABLE 20
HEAT EXCHANGER PERFORMANCE PROGRAM (PERF)
A
Input
B
Output
Overall Dimensions
Fin Dimensions
Hydraulic Diameter, Cold Side
Hydraulic Diameter, Hot Side
Frontal Area
Properties of Fluids
Properties of Heat Exchange
Materials of Construction
Inlet Temperature, Cold Side
Inlet Temperature, Hot Side
Mass Flowrate, Cold Side
Mass Flowrate, Hot Side
Heat Exchanger "j" and
"f" Factor as Function
of Reynolds Number
All input information
Cold Side Reynolds Number
Hot Side Reynolds Number
Cold Side Heat Transfer Coeffecient
Hot Side Heat Transfer Coefficient
Overall Heat Transfer Coefficient, U
Pressure Drop Each Side
NTU's (see the Appendix)
Overall Effectiveness, e
Efficiency Coefficient = Vol/e
Outlet Temperature, Hot Side
Outlet Temperature, Cold Side
93
-------
Figure 31. Typical Blower Performance Curve
-------
Pressure drop on the flue gas side will be determined by the selection
of an induced draft fan. Pressure drops as high as several inches of H.O may
be tolerated with a fairly inexpensive blower (less then $20). If an induced
draft fan is not used we are limited to approximately .02" for gas systems
and .05" for oil fired furnaces.
5.1 SCHEMES 3A AND 4A
A series of runs was made using PERF looking at various plate-fin and
tube fin arrangements and overall dimensions with the objective of achieving
the highes heat transfer within the smallest volume and within certain pres-
sure drop limitations. For an air system the pressure drop limitation on the
air side is controlled by the recirculation blower and system pressure drop.
The results of the PERF runs for the noncondensing heat exchanger and
hand calculations for the condensing heat exchangers are summarized in Table
21 for the plate fin configuration. Similarly, Table 22 tabulates the results
for a fin tube configuration for Schemes 3A and 4A. Figures 32 and 33 illus-
trate the concept and provide more detailed data on the surfaces chosen.
Several surfaces were studied for which heat transfer data were available
from Kays and London (Reference 49). The surfaces shown in Figures 32 and 33
were chosen on the basis of maximum heat transfer surface per unit volume
within the pressure drop constraints. Numerous other plate fin surfaces such
as louvered |fins, strip fins, wavy fins, pin fins and perforated fins were not
considered, and similarly many other fin tube designs could not be explored with-
in the scope of this project. For these reasons the chosen surfaces therefore
do not necessarily represent the optimum configuration of all possible sur-
faces or even for these surfaces but should represent a typical heat exchanger
that might be built.
Notice that the pressure drop for the finned tube approach on the gas
side may be low enough to be adaptable to an oil fired furnace without using
an induced draft fan.
Figures 34 and 35 show the performance in graphical form for various
inlet temperatures for the noncondensing heat exchangers. Figures 36 and 37
show the performance of the condensing plate fin and fin-tube heat exchangers
respectively. These performance curves are only approximate since constant
effectiveness has been assumed.* This assumption does not take into account
the change in heat transfer coefficient with temperature.
This is not true for the condensing portion of the condensing heat exchanger.
The overall effectiveness actually increases with Tp .
95
-------
TABLE 21
PLATE FIN HEAT EXCHANGERS - FLUE GAS TO AIR
Scheme No
Width (in)
Height (in)
Length (in)
No. of Passes
Hydraulic Diameter (ft)
Fin Height (in)
Cell Width (in)
Reynolds No.
Mass Flow Rate (lb/min)
Roncondensing Heat Transfer Coef.
(Btu/hr-ft2°F)
Condensing Heat Transfer Coef.
(Btu/hr-ft2°F)
Total Heat Transfer Area (ft2)
Pressure Drop ("H20)
Inlet Temp (°F)
Outlet Temp (°F)
Overall Effectiveness
Total Heat Transferred (Btu/hr)
Vol/E - Effectiveness
Noncondensing
(3A),(4A-W)
7.137
1.17
15.00
Cold
1
.01259
.544
.195
2646
75
11.69
-
14.45
.123
140
147
Hot
1
.0094
.249
.168
1234
2.07
10.47
-
8.97
1.72
400
181
.84
6785.
149.
Condensing
(4A-C)
15.0
1.508
20.00
Cold
1
.01259
.544
.195
882
75
7.02
-
53.3
.0187
70
77
Hot
1
.0094
.249
.168
480
2.07
7.11
~27
32.45
.82
400
100
.78
14621
471.
96
-------
TABLE 22
FIN TUBE HEAT EXCHANGER - FLUE GAS TO AIR
Scheme No.
Width (in)
Height (in)
Length (in)
Fluid
No. of Passes
Hydraulic Diameter (in)
Tube and Fin Diameter (in)
Fin Pitch (Fins/in)
Tubes/Frontal Area
Total Number of Tubes
Flowrate (Ibs/min)
Reynolds Number
Noncondensing Heat
Transfer Coefficient (Btu/hr-ft2°F)
Condensing Heat Transfer
Coefficient (Btu/hr-ft2°F)
Total Heat Transfer Area (ft2)
Pressure Drop ("H20)
Inlet Temperature ) ftlso See
Outlet Temperature) «9««.35
Overall Effectiveness
Total Heat Transferred Btu/hr
Vol/e - Effectiveness Factor
Noncondensing
3A, 4A-N
1
4
17.6
12.4
Cold
Air
1
.964
-
-
45
45
75
33853
13.8
_
4.02
.263
140
146
Hot
Flue Gas
3
.23
1.737
8.8
3
45
2.07
598
8.0
_
46.1
.075
400
206
.74
6008
1173
Condensing
4A-C
2
4
23.4
17.6
Cold
Air
1
.350
-
-
484
484
75
9070
17.3
_
14.8
.051
70
102
Hot
Flue Gas
4
.154
.975
8.72
6
484
2.07
328
7.64
-27
155
.052
400
99
.815
15351
3068
97
-------
Aie.
filler
14C |47
,O\O 300-&OD 120-140
(»o
Figure 32. Plate-Fin Exchanger
Single Pass Each Side Pressure
Atmosphere Both Sides
98
-------
FLUE
PLUG
OUT
RCOM AIR OUT
iiiiiiiii
ililliiii
» ,012'
-(40° F
TUBE WALL THtCK.NieS'S = . O3O > NiO. OF TUBES= 45
Figure 33. Fin Tube Design
3 passes hot side
1 pass cold side
Pressure ~ atmosphere both sides
99
-------
loooo
'ZDO
f
ISO
o
o
IBC3OO
Figure 34. Performance of the Noncondensing Plate Fin Flue Gas to Air Heat Exchanger
-------
Figure 35. Performance of the Noncondensing Fin-Tube Flue Gas to Air Heat Exchanger
-------
^000
'• tocpoo eru
6O
BOOo
Figure 36. Performance of the Condensing Plate Fin Flue Gas to Air Heat
Exchanger
102
-------
n
^OOoa
100,000
GO%
AIR
/ue
4&O
IN
0
IT
tt
0»
"^oo
Figure 37. Performance of the Condensing Fin-Tube Flue Gas to Air
Heat Exchanger
103
-------
It is of interest to note that it takes approximately the same heat
transfer surface area to go from 400°F to 123°F, noncondensing as it does to
go from 123°F to 100°F condensing. The greater than triple surface area re-
quired is accounted for by the lower heat transfer coefficient in the noncon-
densing regime due to greater open flow area on the air and gas sides.
The physical size and shape of these units are such that they could be
easily placed over the air inlet or outlet of the furnace in much the same
fashion as a filter. For applications to a gas fired furnace the draft diver-
ter would have to be closed off and the sheet metal and duct work to the heat
exchange insulated.
For costing purposes a preliminary selection of an induced draft fan
was made. The requirements for this unit are tabulated in Table 23.
TABLE 23
INDUCED DRAFT FAN REQUIREMENTS
Flow (cfm)
AP inch H20
Temperature
30-40
.02-3
120°F -
• 300°F
Preliminary investigation show that a vacuum cleaner type blower run-
ning at 3450 RPM (normal RPM and pressure is 10,000 RPM and 80 inch SP) would
produce about the right flow and pressure. This blower is readily available
from the leading manufacturers for under $20.
5.2
SCHEME 4W
Only a fin-tube design was determined for Scheme 4W, exchange with a
cold water stream. Figure 38 shows the chosen configuration for noncondensing
unit. Flue gases pass over a bank of forty finned tubes in a single mass and
water flows through a manifold to feed four parallel paths with ten passes
each. The high number of passes are necessary to keep the heat transfer coef-
ficient on the water side relatively high (-100 Btu/hr-ft2°F). Figure 39
shows the chosen configuration of a condensing unit. In this case flue gases
pass over a bank of 128 finned tubes in a single pass and water flows through
a manifold to feed eight parallel paths with sixteen passes each. Table 24
tabulates the design information and base performance calculations for the
noncondensing and condensing unit. The frontal area on the flue gas side for
104
-------
PLUS:
G/V5
C ) C ) ( )
C J L J C 3
c j c :> c i
C J C 3 C 3
1
Z3 ^
Figure 38. Noncondensing Flue Gas to Water Fin Tube Heat Exchanger
(Scheme 4W-N)
105
-------
\Ae\w
our
C 3 C 3( 3C 3( )C 3( 3
C DC 3C 3( 3C 3C 3C 3
C 3 C 3 ( 3 C 3 C 3 C 3 C 3
( 3 ( 3 C 3 C 3 C 3 ( 3 C 3
C 3 C 3 C 3 ( 3 C 3 C 3 C 3
C 3 C 3 ( 3 ( 3 C 3 ( 3 ( 3
CJC 3C 3( 3C 3C DC 3
C 3C 3C 3C 3C 3C 3C 3
i
o
i
«c
3 4-
-
SIDE
Figure 39. Condensing - Flue Gas to Water Fin Tube Heat Exchanger
(Scheme 4W-C)
106
-------
TABLE 24
FIN TUBE HEAT EXCHANGER - FLUE GAS TO WATER
Scheme No.
Width (in)
Height (in)
Length (in)
Fluid
No. of Passes
Hydraulic Diameter (in)
Tube and Fin Diameter (in)
Fin Pitch (Fins/in)
Tubes/Frontal Area
Total Number of Tubes
Flowrate (gal/min, Ibs/min)
Reynolds Number
Noncondensing Heat
Transfer Coefficient (Btu/hr-ft2°F)
Condensing Heat Transfer
Coefficient (Btu/hr-ft2°F)
Total Heat Transfer Area
Pressure Drop ("H20)
Inlet Temperature } Base Condition
> Also See
Outlet Temperature ) Figure 3
Effectiveness
Total Heat Transferred Btu/hr
Base Condition
Vol/e - Effectiveness Coefficient
Noncondensing
4W-N
3.9
3.2
9.75
Cold
Water
10
.350
-
-
4
40
.5
1154
100
-
1.2
-.27
65
113
Hot
Flue Gas
'l
.154
.92
8.72
4
40
2.11
2490
7.94
-
11.48
.21
500
113
.87
11932
139.9
Condensing
4W-C
6.4
4.2
15.2
Cold
Water
16
.350
-
-
8
128
1.00
1257
75.9
-
4.1
.15
65
96.5
Hot
Flue Gas
1
.154
.92
8.72
8
128
2.11
287.4
10.67
42
39
.46
500
112
.73
15758
511.3
107
-------
the condensing heat exchanger was increased to keep the pressure drop down
and maintain reasonable dimensions. As a result the heat transfer coefficient
in the noncondensing region is decreased and the overall volume is slightly
larger than if the frontal area had been kept the same as the noncondensing
heat exchanger.
The condensing heat transfer is considerably lower than the plate fin
case for the air to flue gas exchanger. This is due primarily to the lower
mass flux (lbs/hr-ft2) on the flue gas side due to the greater open area.
Consequently the heat transfer area for the condensing heat exchanger is over
triple the area for the noncondensing heat exchanger.
108
-------
SECTION 6
SYSTEM COST
This section presents the potential savings per year in fuel cost, the
estimated costs for the retrofit schemes designed in Section 5, the relative
costs of new furnace design, costs of conventional designs, and a summary of
the costs of retrofit devices on the market.
6.1 POTENTIAL SAVING AND PAYBACK PERIOD
The potential savings for a retrofit application will depend on the
flue gas temperature (for a given excess air level), the cost of fuel, and the
efficiency of the device or exit gas temperature. Fuel costs vary from loca-
tion to location, depending on fuel type (oil or gas), availability, and the
current political situation around the world. Table 25 gives an indication
of the cost of natural gas in a number of cities as of May 1974 (Reference 51).
The trade journal, Fuel Oil and Oil Heat, indicates that a September
1974 fuel oil price is $.36/gal which is about $.27/therm (Reference 52).
Figure 40 shows the potential dollar savings per year as a function of
flue gas temperature and exit temperature. This curve is based on 100,000 Btu/
hr furnace operating at 60 percent excess air, fuel cost of $0.2/therm and is
analogous to Figure 26 in Section 3. The assumption is made here that the
ratio of the potential heat saved to the heat input to the furnace is the same
as the therms saved per year to the total therms required per year. That is,
qs/qF = Ts/TT
where
q = Heat Recovered Btu/hr (from Figure 1)
s
qp = 100,000 Btu/hr
T = Therms saved per year
S
TT = 1040 therms/year [from Hittmann Report (Reference 10)] for space
heating
109
-------
TABLE 25
FUEL COST
$/THERM
(Reference 51 )
City
San Francisco
Los Angeles
San Diego
Baltimore
Boston
Chicago
Houston
Washington
Seattle
N.Y.C
Natural Gas
May 1974
.110
.135
.150
.176
.335
.142
.134
.765
.223
.261
110
-------
Basis: 100,000 Btu/hr Furnace
1040 Therms Per Year for Space Heating
$.20/Therm Fuel Cost
T_ = Flue Gas Temperature Upstream
U
800
OUT
Figure 40. Potential Saving as a Function of Flue Temperature for Retrofit Heat Recovery Device
-------
Then the dollars saved per year is equal to DSQ = .20 T
D_ = .00208 q
so s
If higher fuel costs are experienced then this number may be multiplied
by the ratio of fuel prices or
Ds = 5 - C - DSQ
where D = Fuel savings in $/year based on Figure 41
SO
C = Cost of fuel $/therm
If in addition a flue damper is used, an additional 100 (Reference 10)
to 250 (Reference 53) therms per year may be saved or from $20 to $50 per year.
This can in many cases represent as much savings potential as a heat recovery
device.
Using Figure 40 as a basis, a curve was generated for the payback
period versus equipment cost and heat recovered. This curve, Figure 41 is
based on a 7 percent interest rate using the present worth technique (Refer-
ence 54) as outlined below.
DSo = I (erf - 7% - n)
where I = Investment in dollars
Ds = Fuel savings per year
(erf - 7% - n) = Capitol Recovery Factor @ 7% for n years
[see Table E-14, Grant and Ireson (Reference 54)]
(1 + i)n - 1
i = .07
This curve also assumes the fuel costs per therm remains constant over
the years. Actually, of course, the payback period will be shorter if the
fuel costs increase with time. As an example, it can be shown that the dol-
lars saved in fuel cost is then equal to:
Term A Term B
112
-------
Basis: 100,000 Btu/hr furnace
1040 therms/year nominal usage
7% rate of return
$.20/therm fuel cost
300 . 350
I($) Initial Investment.
450
500
550
600
Figure 41. Payback Period as a Function of Heat Saved and Initial Investment
-------
where
AD = additional increase in fuel cost each year
s
(gf - 7% - n = factor to convert a Gradient Series to a Equiva-
lent Uniform Annual Series at 7% for n years.
(See Table E-23, Reference 54)
If we let
I = $200
D = $42.4/year
S
AD = $4.24/year (10% increase)
S
Then the following tabulation may be computed from the tables of
Reference 54.
4
5
6
Term
a
59.0
48.6
41.8
Term
b
6.02
7.89
9.75
D
52.97
40.71
32.05
Interpolating yields a payback in 4.8 years as opposed to 6 years as
given by Figure 41.
6.2
COST OF RETROFIT UNITS
Estimates were obtained from ten heat exchanger fabricators for typical
plate-fin and fin-tube designs (Scheme 3A). Prices for production of 1000
units and 10,000 units per year were requested. Both designs were based on
using a low grade stainless steel throughout. Table 26 summarizes the range
of prices obtained.
TABLE 26
HEAT EXCHANGER COSTS
Plate Fin
(Figure 32)
Fin Tube
(Figure 33)
1000 Units/Year
$50 - $400
$100 - $600
10,000 Units/Year
$24 - $250
$50 - $500
114
-------
From these data estimates were then made for each scheme including fac-
tors such as an induced draft fan, ducting changes, insulation, and installa-
tion costs. These data are summarized along with the payback period based on
Figure 41 in Table 27. the Dolin, Isothermics and Vent-0-Matic devices are
also included for comparative purposes.
This table shows that in terms of payback the flue damper is the best
buy. It also reveals that the most promising devices are those that are ap-
plied to oil fired furnaces because: (1) The oil fired furnaces are initially
less efficient (higher flue gas temperatures), (2) It takes more hardware to
convert a gas furnace (replacement of the draft diverter) and (3) The cost of
oil is higher. It should be remembered that the estimated costs are rather
speculative and could be considerably higher. Also if one assumes a higher
interest reate (for example the interest rate to secure a loan (approximately
14 percent) rather than a nominal rate of return from a savings and loan), the
payback period will increase in all cases. It should also be remembered that
as the price of fuel increases so will the price to manufacture these items.
6.3 NEW FURNACE DESIGNS
At this time none of the new furnace schemes has been designed in
enough detail to allow an accurate estimatation of costs. However, we should
be able to set a reasonable upper boundary on system costs to be economically
feasible.
Assume for the sake of argument that the following improvements to
the heating system produce the indicated savings in energy consumption (com-
pared with the fuel consumption for the unidentified case):
Improvement Assumed Savings (%)
Improved furnace efficiency 10
Furnace modulation 25
Flue damper 15
Total 50
Yielding a total reduction in energy consumption of 50%. At an assumed fuel
cost of $.20/therm this would amount to D = (0.2) x (.50) x (1040) =$104/year.
s
Next we must assume some value for an assumed lifetime of the furnace.
Ideally, the furnace should last for 15-25 years. On the other hand, a typi-
cal average residence time for a homeowner is more on the order of 5 years.
115
-------
TABLE 27
SYSTEM COSTS AND PAYBACK PERIOD
Scheme Number
Exchange Heat W/
Fuel
Heat Exchanger2
Ducting & Misc.3
Insulation
Induced, Draft Fan
Installation"
Total Cost
Heat Saved
(Btu/hr)5
Fuel Cost Saving
Dollar/yr
Payback Period
(Years)
3A
Air Out
Gas
100
15.00
7.50
15.00
40.00
177.5
4,223-
12,000
9-25
10 -»• »
3A
Air Out
Oil1
100
10.00
5.00
15.00
32.00
162.00
2,400-
17,400
26-49
3.75-8.5
4A-C
Air In
Gas
150
30
10
15
100
305
11,800-
16,800
25-35
13.5-27
4A-C
Air In
Oil1
150
20
7.50
15.00
92.00
284.5
16,800-
24,000
47-67
5.5-7.5
4W-C
Water
Gas
300
15
7.50
15.00
72.00
409.5
13,308-
17,718
28-37
22-45
4W-C
Water
Oil1
300
10
5.00
15.00
64.00
394.0
17,718-
26,396
50-74
6.5-11.5
Dol in
Air
Oil1
130.00
15.00
-
-
24.00
169.00
3,000-
5,300
8-15
22 •* 100
Isothermics
Air
Oil1
100
15
-
-
16
131
5,000-
12,500
14-35
4.5-15
Ventomatic
-
Gas
-
-
-
-
-
87
104 *
390s
21-78
1.2-5
'For oil systems the fuel price is based on $.27/therm ($.35/gal)
2For plate fin heat exchanger except for water/gas heat exchange which is fin-tube; costs estimated from data of Table 26.
'Includes closing oft integral draft diverter and installation of in-duct draft diverter for gas systems; Dol in and Isothermics,
assumes heat is routed into main air system.
"Installation costs will vary depending on labor rate; assumption here is $8/hr.
5See Table for assumptions and supporting data
6For Ventomatic, heat saved is expressed in therms/year (Reference 55).
-------
It seems unlikely that a homeowner would thus be willing to pay for a furnace
lifetime longer than, say, 7-10 years unless he was able to be assured of a
return on his investment when he sold the house. For the moment let the
lifetime or payback period be a variable.
In addition, assume that fuel costs will increase uniformly at 10 per-
cent of the first year at an assumed price of $.2/therm. Then there will be
an additional $10.40/year savings added each year. The initial investment
delta will then be equal to:
AT - 104. + 10.4(gf - 7% - n)
ai (erf - 7% - n)
with (gf - 7% - n) and (erf - 7% - n) as defined in Section 6.2. Figure 42
presents the results of this expansion for n's from 2 to 25 years. This
shows that if a homeowner accepts a 25-year lifetime or payback period, he
should be willing to invest up to $2250 to achieve the assumed improvement in
efficiency. However, because the historical philosophy of buying has been
one of lowest initial cost, it may be quite difficult to convince the public
to purchase on the basis of a long term total investment.
In fact, however, the assumed 50 percent savings can probably be
achieved for an additional $500 to $1000 with the new designs. Figure 42
shows the payout could be achieved within 5 to 10 years, or perhaps sooner
if fuel prices increase at a faster pace than assumed.
As a support example, the Westinghouse Utilization Project (Reference
56) showed that in most U.S. cities the total annual cost of a heat pump,
more costly than conventional equipment, was lower than either a gas or oil
system, for typical conditions. Table 28 presents this cost advantage for a
number of U.S. cities.
6.4 COST OF CONVENTIONAL DESIGNS
There seems to be a wide spread in furnace costs for a typical 100,000
Btu/hr furnace. Gas systems vary anywhere from $200 to $600 depending on
quality, lifetime guarantee, sophistication of controls, and ability of the
fan to produce the high air flow rates required for air conditioning. All
AGA approved furnaces guarantee the 80 percent steady state efficiency. New
oil fired units are selling for $500 to $1200 with efficiency of 75-80 per-
cent. Heat pump systems are currently selling for around $1600 and total
heating and air conditioning systems sell for $1100 to $1600.
117
-------
ZfoD
looo
\*>00
tflOOO
n
Figure 42. Initial Investment Increment vs. Lifetime or Payout Period
-------
TABLE 28
ANNUAL SAVINGS TO HOMEOWNER USING A
HEAT PUMP VS. EQUIVALENT COMFORT-CONDITIONING SYSTEMS
(Reference 56)
Minneapolis
Milwaukee
Pittsburgh
Oklahoma City
Atlanta
Sacramento
Tampa
Fuel Rates (10)
Electric
tt/KWH)
1.45
1.56
1.59
1.00
1.30
.88
1.85
Gas
U/Therm)
10.5
12.9
11.9
7.7
8.9
9.036
12.0
Annual Fuel Savings - $
Heat Pump
Vs. Gas
-39
40
15
23
24
43
11
Heat Pump
Vs. Oil*
85
92
93
111
84
98
19
Total Annual Savings - $
Heat Pump
Vs. Gas
-60
19
-6
2
3
22
-10
Heat Pump
Vs. Oil*
111
118
119
137
110
124
45
M
Includes all adjustment and surcharges except fuel adjustment.
Since oil price is increasing rapidly, a fixed value of $.20/gallon was used here.
-------
However, of the total furnace system sold during a year a large percen-
tage are for new homes and particularly for tract developments. In these
situations the lowest initial cost system is undoubtedly preferred. (Manu-
facturers have stated that a $2 increase in manufacturing cost is a signifi-
cant factor). The price of tract furnace systems may be considerably lower
than the above retail prices. Convincing tract developers to utilize a more
expensive furnace may be a more formidable task than convincing the public.
6.5 CONCLUSIONS
The preliminary estimates of this section indicate that the amount of
savings provided by a new high efficiency furnace system design appear attrac-
tive, with payback periods in the 5- to 10-year range, and at costs which are
roughly double the cost of a current system. However, although the large
scale economics appear attractive, formidable social and institutional ob-
stacles would act to prevent the widespread use of such new furnace designs.
New furnaces are sold to a public which is extremely conscious of initial cap-
ital cost and relatively unaware of energy management and engineering. This
is particularly true in the new residence market, which accounts for a very
appreciable portion of furnace sales. Heat furnace design has settled into a
nominal efficiency range of 70 to 80 percent reflecting a conjunction of mar-
ket forces which have integrated the typical effects of initial costs, fuel
costs, home turnover rate, and purchase behavior in buying new and used homes.
However, fuel prices and inherent rates tend to counteract, and the apparent
economic optinum efficiency has shifted upward only slightly. Other reasons,
such as long term conservation of valuable fuels, make the desired efficiency
somewhat higher still, but it will be very difficult to integrate such new
factors into the market system. It may be necessary to consider federal ef-
ficiency standards.
120
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SECTION 7
CONTROL OF AIR POLLUTANT EMISSIONS
FROM RESIDENTIAL HEATING EQUIPMENT
7.1 INTRODUCTION
The preceding sections of the present study have dwelt on the possible
methods for increasing the efficiency of existing residential furnaces. It
was determined that a number of controlling variables exist for this purpose,
such as modifying heat exchanger design and reducing the frequency of cyclical
operation. Likewise, there exists a set of options for the control of air
pollutant emissions from gas-and oil-fired heating systems. This section is
concerned with defining the most important of these emission reduction
techniques.
Distillate oil and natural gas heaters account for 90 percent of the
residential heating units in the U.S. (Reference 57). The actual contribu-
tion of fuel combustion in this equipment to the total national air pollu-
tant loading (summation of mass of particulate, SOX, NOX, CO, and unburned
hydrocarbons) is unclear. One investigator estimated that air pollution
from the combination of residential and commercial heating sources consti-
tutes about 10 percent of the national total (Reference 58). This figure,
however, may be outdated; the source was published in 1964. Fuel usage and
emission factors were the basis for this estimate.
Another data source, the National Emission Data System (NEDS), does
not compile information for sources that emit less than 25 tons/year of any
pollutant. This limitation causes the exclusion of residential heating from
consideration. From all indications, however, their contribution to the
nation's total emissions probably falls in the 1-10 percent range. In any
case, their impact was deemed sufficiently significant that EPA has insti-
gated an emission reduction R&D program (see Section 7.3).
Typical emission levels are presented in Table 29. The test compari-
sons between three gas furnaces and three oil furnaces indicate that the
level of gaseous pollutant emissions from the gas burners is comparable to
those from equivalent size oil burners, with particulate being a problem only
from the latter. Compared to other sources of air pollution, the levels of
121
-------
TABLE 29
EMISSIONS FROM NATURAL GAS- AND OIL-FIRED BURNERS
(Reference 57)
to
to
Burner
Manufacturer
Gas-fired:
Williamson
furnace
Bryant boiler
Bryant furnace
Oil-fired:
Union (Pure)
ABC Mite
ABC Standard
(Model 45)
Stoichiometric
Ratio
1.20
1.40
1.60
1.20
1.38
1.53
NO, g/106
cal input
0.084
0.115
0.112
0.104
0.115
0.071
0.102
0.096
HC, g/106
cal input
0.0007
0.0014
0.0075
0.0032
0.0055
0.0055
0.0055
0.0055
CO, g/106
cal input
0.022
0.099
0.032 .
0.051
0.046
0.046
0.046
0.046
Average Emissions
Average Emissions
-------
HC and CO from these properly adjusted furnaces are very low (Reference 57).
The remainder of this section will review the major options available
for combustion or post-combustion control of emissions from gas- and oil-
fired domestic furnaces. The principal recently-completed or current re-
search programs aimed at reducing these emissions are described as well.
7.2 CONTROL STRATEGIES FOR EMISSIONS FROM RESIDENTIAL HEATING SYSTEMS
The three major options for reducing pollutant emissions from com-
bustion sources include fuel substitution, combustion process modification,
or post-combustion control. Fuel switching (to gas) would logically be ap-
plied only to oil-fired furnaces, mainly for particulate abatement. However,
the associated equipment conversion required by such a move would be economi-
cally unfeasible. This leaves combustion and post-combustion control as the
most viable means for achieving emission reduction goals. These are dis-
cussed separately in the following subsections.
7.2.1 Combustion Process Modification
Reducing emissions evolved by flames by modifying the combustion pro-
cess itself has, in recent years, gained popularity as a NO control strate-
Ji
gy for industrial and utility boilers. The same principles can be applied
on a much smaller scale but with equal validity to residential heating sys-
tems. As with the larger scale combustion equipment, care must be taken to
avoid emissions trade-off problems, that is, increasing one pollutant species
due to a control aimed at reducing another.
The important combustion control emission reduction strategies include:
• Excess air level adjustment
• Modification of combustion chamber design
• Installation of flame retention burners
• Ignition system state-of-repair
• Regular service and maintenance
Descriptions of these control options appear in Table 30, with comments des-
cribing the relevant effect of each option.
123
-------
TABLE 30
COMBUSTION CONTROL STRATEGIES FOR
REDUCING AIR POLLUTANTS FROM
RESIDENTIAL HEATING EQUIPMENT
Control
Strategy
Impacted
Pollutant Emission
Comments
References
Excess air level
adjustment
NO
• As excess air is increased, CO
HC, and smoke pass through a
minimum, but NO passes through
a maximum
• Optimum pollutant and thermal
efficiency level occurs at a
stoichiometric ratio greater
than one (-1.6 for oil burners).
59, 57, 60
Combustion chamber
design
NO
CO
HC
Smoke/particulate
• Combustion chamber design affording
long residence time at high temper-
ature minimizes smoke, particulates,
CO, HC, but may increase NO
• Refractory-lined chamber affords
better combustion and lower emissions
57, 60, 61
Flame retention Smoke
burners
0 Oil burners with retention-type end
cones give superior emission and
efficiency performance
57, 60
Ignition system
condition
NO
• No effect on HC and smoke
• Minimal effect on NO
57, 60
Service and
maintenance
CO
HC
Smoke/particulate
• Equipment state-of-repair very
important for providing breadth
for reducing emissions by other
methods
t Oil nozzles should be changed
each season
t Air filter should be replaced
regularly
59, 57, 60
124
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7.2.2 Post-Combustion Control
The second alternative available for reducing undesirable furnace
emissions is the treatment of the combustion product gases, usually by a
retrofit device installed in the flue. Most of the candidate devices are
designed to abate a single pollatant, and combinations of them may be used
for multiple pollutant species reduction.
The principle types of flue gas treatment (FGT) devices for possible
application to home heaters include the following:
• Fabric filters
• Wet scrubbers
• Wet, packed beds
• Activated charcoal filter
• Cyclone
• Combinations of devices
Table 31 describes these devices in greater detail.
In all, the feasibility of most of these devices for residential
heating applications is unknown. The success attained so far by combustion
process modification may negate possible reduction benefits afforded by the
less well-defined FGT devices.
7.3 PRINCIPAL RECENT OR CURRENT RESIDENTIAL EMISSION REDUCTION R&D EFFORTS
As mentioned in Section 7.1 of this report, there is a significant
amount of industry and government-sponsored research and development effort
currently being expended in the area of reducing emissions from residential
heating equipment. These activities are described in Table 32. Information
on level of funding was not available.
'7.4 CONCLUSIONS
The following general conclusions have been reached concerning emis-
sion control of residential furnaces:
• The contribution of residential furnace emissions to the nation's
totals for each type of pollutant should be more closely defined.
This can be done by obtaining updated emission factors and furnace
inventories, as well as fuel usage figures. When the actual con-
tribution is known, a more valid decision base will be available
for R&D program planning efforts.
125
-------
TABLE 31
POST COMBUSTION CONTROL (FLUE GAS TREATMENT)
STRATEGIES FOR AIR POLLUTANTS FROM
RESIDENTIAL HEATING EQUIPMENT
Control Impacted
Strategy Pollutant Enriss.ion
Comments
References
Fabric Filter
Smoke/particulate
t Most high efficiency 62, 63, 64
filters are not designed
for high stack temperatures
• "Absolute" - type filter
(to 500°F) cause excessive
Ap (~T"W.C.)
Wet Collectors Smoke/particulate
• Some industrial uses, but 65, 66, 63
feasibility for residential
furnaces yet to be determined
i Small units used in electronic
industry may be applicable
Wet, packed
beds
Smoke/parti culates
HC
• Efficient particulate and
odor removal method
• Applicability for residential
use not yet determined
67, 68
Activated
charcoal
filter
HC
• Used frequently to remove 63, 69, 70
odors and solvent aerosols
• Max. temperature = 100°F; may
be practical for furnace flue
gas treatment if stack tempera-
ture can be reduced
Electrostatic
precipitator
Smoke/particulate
• ESP's designed for commercial/ 71, 72, 73,
residential air filtering not 64, 74
usuable at high temperatures
found in stacks (plates warp)
t Particle agglomeration on
plates possibly a problem
• No known ESP specifically
designed for residential furnace
use
Cyclone
Particulates
• Feasibility for residential use 66, 75, 71
unknown
Combinations
of filtration,
ESP, activated
charcoal
Particulates
HC
• Three step system
t Roughing filter
• ESP for fine particulate
• Activated charcoal for HC
• System this elaborate
probably not warranted
70
126
-------
TABLE 32
PRINCIPAL RECENT OR CURRENT RESIDENTIAL EMISSION REDUCTION
R&D EFFORTS
Agency and/or
Organiation
Investigated
Pollutant(s)
Nature of Study
References
EPA
CO
HC
Smoke/particulates
• Define major emission
level control variables
t Recommend emission
minimization methods
through combustion
controls
• Status: Continuing
57, 60
Battell e NO,,
cox
HC
Smoke/particulates
• Field investigation of
emission from oil-fired
equipment
0 Found serious emission
trade-off difficulties if
tuning to low smoke level
performed without monitor-
ing instrumentation
• Made comparisons of measured
emissions with EPA emission
factors
• Status: final report submitted
June, 1973
59
Maiden
• Study of Air Pollution from
Intermediate Size Fossil -
Fuel Combustion Equipment
• Status: Final report submitted
July, 1971
61
American Gas
Association
(sponsor) :
t Institute
of Gas
Technology
(IGT)
NOV
The Research
Corporation
of New
England
(TRC)
co
HC
Smoke/particulates
• Study of fundamental mechanisms
of the formation and suppression
of NOX in natural gas combustion
t Not strictly concerned with
residential heating units, but
results will be relevant
• Status: ongoing
• Measuring the environmental
impact of domestic gas-fired
heating systems
• Emissions being related to
ambient air quality
• Status: ongoing (through
1973-74 heating season)
18
76
127
-------
Combustion process modification is clearly the most viable short-
term option available for emission reduction.
For abating such pollutants as particulates emitted during fur-
nace start-up, the application of some of the candidate FGT de-
vices may be warranted (i.e., high temperature fabric filters).
Acquisition of detailed cost information on FGT devices, in addi-
tion to continued applied research on devices feasible for use on
domestic furnaces, are required before the cost/effectiveness of
such devices can be fully assessed.
128
-------
SECTION 8
POTENTIAL MARKET
The potential market for either a retrofit device or a new high effi-
ciency home furnace will depend in general on the following factors:
• New home building
• Fuel availability
• Fuel price
• Local ordinances
• AGA or similar approval
• Proof of economic viability
• National interest - fuel saving, emission prevention
• Advertising and consumer education
• Climate
• Furnace age and condition
Proof of economic viability includes overcoming the lowest initial
price economic philosophy of private homeowners or tract developers as dis-
cussed in Section 6 on system costs. Ordinances and utility companies in
many communities will presently not allow any device in the flue which could
cause blockage. Approval of a heat recovery device which provided a safety
vent in case of blockage would probably be fairly easy especially if AGA or
U.L. approval was obtained. However/ AGA approval is not always easy to ob-
tain. For example, the Vent-0-Matic device was initially approved by AGA,
then rescinded and only given approval for installation on new furnaces. The
whole matter was brought to the attention of the Federal Power Commission,
Federal Trade Commission and Senate Anti-Trust Committee and is currently
under investigation. The issue is expected to be resolved by October 1974
(Reference 55). The Diermayer vent damper devices was not given approval by
AGA and therefore is not being sold at this time in the U.S., although it has
been in use in Europe for over 40 years.
129
-------
Fuel price and availability may either be a force in favor or aqainst
sales of such a device. For example, on the West Coast, the winters are
fairly mild, so far qas is plentiful and remains relatively cheap compared
with prices in other parts of the country.
The potential market for new furnaces will depend on the housinq
building market or for replacement units the number of old furnaces which need
replacing. Table 6 showed that in 1973 over 2 million gas fired furnaces were
sold as well as over 700,000 units, each of oil fired central air, vented wall
gas furnaces and gas fired direct heating equipment. A total of 4,892,260 of
all type units were sold in 1973, adding and/or replacing part of the 58 mil-
lion heating systems in the U.S. (1970). New units in 1973 therefore accounted
for about 8.4 percent of the 1970 census of heating systems.
From the U.S. Census data and the GAMA data on total furnace systems
sold, it was determined that approximately 36 percent of the furnaces sold
during 1963 were for new housing, and the reminder were replacement units.
Obviously this number will vary from year to year but using this figure, it
indicates that about 5 percent of the furnace population will be replaced
each year.
8.1 POTENTIAL MARKET ESTIMATE
If we assume that 10 percent of the new and replacement units could be
high efficiency units, this represents a market of about 500,000 units per
year.
Table 33 presents the results of an estimate of the market for a heat
recovery device. It was assumed that only central air and central water or
steam systems could be retrofited and that the units converted in the
Southern and Western regions would only be on the order of 1 percent. Twenty
percent conversion was assumed in the Northeast and North Central regions.
This shows a potential of over 6 million units.
8.2 NATIONAL REDUCTION IN FUEL CONSUMPTION
The assumption was made that 500,000 new high efficiency units are
sold each year and that the 6 million retrofit devices are sold according to
the schedule in Table 34 with 500,000 units each year thereafter.
In addition we assumed that the new high efficiency units use 50
percent less fuel per year, that the retrofit devices decreased the older
unit's fuel consumption by 20 percent and the nominal fuel usage was 1040
therms/year. From these assumptions and the data in Table 34 the total
130
-------
TABLE 33
ESTIMATE OF HOT WATER AND CENTRAL AIR
FURNACE INSTALLATION FOR 1974
BY REGION (MILLIONS)
Total
Units
Assumed
Converted
Percent
Converted
Total
Units
NE
15.0
20%
3.0
NC
15.9
20%
3.18
S
8.95
1%
.09
W
5.79
1%
.06
All
45.64
13.87
6.33
NE = Northeast
NC = North-central
S = South
W = West
131
-------
TABLE 34
RETROFIT SCHEDULE
Year
1
2
3
4
5
6
7
8
9
10
•
•
Retrofit Units
Sold
2.0 x 106
1.0 x 106
0.5 x 106
0.5 x 106
0.5 x 106
0.5 x 10s
0.5 x 106
0.5 x 106
•
•
•
•
Accumulated
Retrofit Units Sold
2.0 x 106
3.0 x 106
3.5 x 106
4.0 x 106
4.5 x 10s
5.0 x 106
5.5 x 106
6.0 x 106
*
•
•
•
Accumulated
New Units Sold
0.5 x 106
1.0 x 106
1.5 x 1
2.0 x 1
2.5 x 1
3.0 x 1
3.5 x 1
4.0 x 1
132
-------
national energy savings as a function of a year were calculated. These sav-
ings and the split between gas and oil are presented in Figure 43. The split
between fuels is based on the 1970 census data of the distribution of furnaces
according to fuel. Figure 44 and 45 show the annual gas saving in ftVyear
and oil saving in barrels/year.
If these products were available for production in 1975, they could af-
fect the total U.S. energy consumption and total space heating energy consump-
tion as tabulated in Table 35. This table indicates that after 8 years resi-
dential space heating energy consumption would be reduced by 3 percent. This
represents about .33 percent of the national total.
133
-------
Figure 43. Residential Fuel Saving Per Year
Retrofits Units
New High Efficiency Furnaces
-------
I-'
CO
Figure 44. Savings Per Year
Retrofit Units
New High Efficiency Furnaces
-------
Figure 45.
Oil Saving Per Year
Retrofit Unit
New High Efficiency Furnaces
-------
TABLE 35
ENERGY SAVINGS
Years
1974
1975
1976
1977
1978
1979
1980
1981
1982
nth
Year
0
1
2
3
4
5
6
7
8
Predicted Total Annual
Energy Consumption U.S.
(Reference 77)
78 x 10
80 x 10
83 x 10
86 x 10
89 x 10
91 x 10
94 x 10
96.5 x 10
99.0 x 10
Space
Heating
8.6 x 10
8.8
9.1
9.46
9.8
10.0
10.3
10.6
10.9
Savings
0
.07
.11
.15
.19
.22
.26
.30
.33
Percent of
Space Heating
0
0.8
1.2
1.58
1.94
2.20
2.52
2.83
3.02
Percent of
Total
0
.088
.132
.174
.213
.242
.277
.312
.332
137
-------
SECTION 9
CONCLUSIONS AND RECOMMENDATIONS
9.1 CONCLUSIONS
This study has produced the following conclusions:
• Very little is known about the actual operating efficiency of resi-
dential heating units. This efficiency is influenced by hardware
design and the on-off cycle (which in turn depends on many factors:
ambient conditions, thermal load, thermostat setting), aerodynamic
conditions, and by condition, adjustment, and maintenance factors.
Nominal steady state efficiencies typically range from 70 to 80
percent, but actual operating efficiencies may range from 40 to
75 percent; lack of this kind of information hampers the evaluation
of all proposed improvements.
• A heat recovery device to recover the sensible heat can be econo-
mically manufactured and sold if the flue temperatures are high
enough (>500°F to avoid condensation). This concept is represented
by the Isothermic and Dolin device.
• A heat recovery device to recover the sensible and latent heat will
be difficult to accomplish within the current economic framework.
• Considerable energy (up to 30 percent of the heating load) may be
conserved if the supply could be closely matched to the load by
modulating and closer matching of the furnace to the structure of
heating load.
• Considerable energy (up to 20 percent) could be saved by closing
of the flue during burner off periods.
• The load could be greatly reduced by greater use of insulation and
prevention of air infiltration.
• A high efficiency furnace for new installation could probably be
designed to achieve an overall efficiency greater than 80 percent
within the current economic structure.
138
-------
9. 2 RECOMMENDATIONS
The present study has been of limited scope and amounts to a prelimi-
nary survey activity. All conclusions noted above could benefit from more
detail and a more through testing of alternative assumptions, where data were
lacking or uncertain. With these concepts in mind, the following recommenda-
tions regarding the direction and emphasis of future work are presented.
9.2.1 General Recommendations
1. Obtain actual operating data by measurements on typical furnaces
in typical installations. Define achieved efficiencies in detail
and relate to operating conditions, particularly to on/off cycle
times and modulation aspects. This information will provide the
detailed data base for all future work.
2. Study British and European design practice and current research
activities. Information from these high fuel cost areas will form
a valuable supplement to this study.
3. Survey state of the art in furnace performance prediction techni-
ques, especially those which can account for cyclic effects. Ob-
tain and develop a suitable predictive code, and verify it against
typical data from Recommendation 1.
9.2.2 Retrofit Device Recommendations
4. Continue to monitor commercial and legal progress of retrofit vent
dampers and of noncondensing flue gas devices. Test typical de-
vices to determine actual performance and define possible improve-
ments. Coordinate with Recommendation 2 curve.
5. Refine the design exercise on condensing flue gas devices of
Section 5 and 6 to further define the apparently marginal attrac-
tiveness of these systems.
9.3.3 New Design Recommendations
Probably the most fruitful work would be to explain in much further de-
tail than has been possible here the possibility of a high efficiency modu-
lated furnace concept. Although commercial research of a proprietary nature
continues in this area, the apparent progress does not seem commensurate with
the promise.
139
-------
Recommended components in this activity include Recommendations 1 and
3 above, followed by tasks to:
6. Predict efficiency of proposed modulation schemes by analytical
techniques; identify cycles to optimize operating parameters data.
Modify cycle to see how to improve efficiency.
7. Analytically predict the effect on heat transfer due to modulating
output.
8. Explore methods of modulation
• Vary gas flow rate
• Use multiple burners in various combinations
• Heat capacitance/hot water systems
9. Develop heat load detector and furnace controller (see Section 6)
10. Modify an existing furnace for modulated mode
11. Design a complete new furnace using either the submerged combustion
or catalytic combustion in conjunction with the modulated concept
12. Build a prototype unit and test
13. Relate the progress of this design and development effort to:
• Commercial and research developments in alternative heat pump/
all electric systems (including solar-assist components)
• Other integrated energy management system programs, including
total-energy and MIVS
• Household energy conservation programs which will be affecting
thermal load data for new construction
9.3.4 Emissions
With regard to emission control devices three specific areas of study
are recommended:
14. Determine the real contribution of residential emissions to environ-
mental air quality
15. Further investigate post combustion control devices, if required
16. Define the potential of the modulated furnace concept (Recommenda-
tions 6-11) to reduce the high peak emission associated with start-
up and shutdown periods.
140
-------
REFERENCES
1. Stanford Research Institute, "Patterns of Energy Consumption in the
United States," Office of Science and Technology, Executive Office of
the President, Washington DC 20506, January 1972.
2. Atomic Energy Commission, Oakridge National Laboratory, "Inventory of
Current Energy Research and Development," Prepared for the Committee on
Science and Astronautics, U. S. House of Representatives, 93rd Congress,
Volume I, II and III, Washington, January 1974.
3. "Conservation and Efficient Use of Energy," Joint Hearings before Certain
Subcommittees of the Committees on Government Operations and Science and
Astronautics, House of Representatives, 93rd Congress, Parts I-V, June -
July 1973.
4. U. S. Department of Commerce, National Bureau of Standards, The Center
for Building Technology, Energy Conservation for Buildings Bulletin
1-2/Cbt.
5. National Bureau of Standards, "Design and Evaluation Criteria for Energy
Conservation in New Buildings," NBSIR 74-452, U. S. Department of Commerce,
Prepared for National Conference of States on Building Codes and Standards,
February 27, 1974.
6. NBS Technical Note 789, "Technical Options for Energy Conservation in
Buildings," National Conference of States on Building Codes and Standards
and National Bureau of Standard Joint Emergency Workshop on Energy Con-
servation in Buildings held at U. S. Department of Commerce, Washington
DC, June 19, 1973.
7. Achenback, P. R. and Coble, J. B., "Site Analysis for the Application of
Total Energy Systems to Housing Developments," Presented at the 7th Inter-
society Energy Conversion Engineering Conference, San Diego, September
25-29, 1972.
8. Coble, J. B. and Achenbach, P. R., "Description of Equipment and Instru-
mentation for a Field Study of a Total Energy System in an Apartment De-
velopment," Presented at 7th Intersociety Energy Conversion Engineering
Conference, San Diego, California, September 25-29, 1972.
9. Hittman Associates Inc., "Residential Energy Consumption," Phase I Report,
HUD-HAI-1, Department of Housing and Urban Development, Office of the
Assistant Secretary for Research and Technology, March 1972.
10. Hittman Associates Inc., "Residential Energy Consumption Single Family
Housing," Final Report, Report No. HUD-HAI-2, Office of the Assistant
Secretary for Policy Development and Research, Department of Housing and
Urban Development, March 1973.
11. Hittman Associates Inc., "Residential Energy Consumption, Multi-Family
Housing Data Acquisition," Report No. HUD-HAI-3, Department of Housing
and Urban Development, Office of the Assistant Secretary for Research
and Technology, October 1972.
12. Hittman Associates Inc., "Residential Energy Consumption - Verification
of the Time-Response Method for Heat Load Calculation," Report No. HUD-
HAI-5, Office of the Assistant Secretary for Policy Development and Re-
search, Department of Housing and Urban Development, August 1973.
141
-------
REFERENCES (continued)
13. Department of Housing and Urban Development Policy Development Research,
The Applicability of the Residential Energy Consumption Analyses to Var-
ious Geographic Areas, Report No. HUD-HAI-6.
14. Lokmanhekim, M. L. , et.al., "Evaluation of Heating Loads in Old Residen-
tial Structures," Hittmann Associates, Report No. HUD-HAI-7 or HAI-H-1654,
January 1974.
15. Fox, John, Fraker, Harrison, Jr., Grot, Richard, Harrje, David, Schorske,
Elizabeth and Socolow, Robert, "Energy Conservation in Housing. First
Year Progress Report," Center for Environmental Studies - Report No. 6,
Princeton 4, NSF/RANN Grant No. GI-34994, July 1, 1972 to June 30, 1973,
December 1973.
16. Movers, John C., "The Value of Thermal Insulation in Residential Construc-
tion: Economics and the Conservation of Energy," ORNL-NSF-EP-9, Oak Ridge
National Laboratory, December 1971.
17. Private Telecommunication with Mr. Holtz, June 5, 1974, of California
Polytechnic College, San Luis Obispo, California.
18. American Gas Association, Research and Development 1973 and Telecommunica-
tion with Pete Sussey, Manager Environmental and Energy Systems.
19. DeWerth, D. W., Schaab, M. S. and Hellstern, P. A., "New and Improved
Methods of Heating Localized Areas In and Around the Home," American Gas
Association Research Bulletin 99, February 1964.
20. Griffiths, J. C. and Niedzwiecki, R. W., "An Evaluation of Some New or
Different Ways to Heat the Home," American Gas Association Research Bulle-
tin 101, May 1965.
21. DeWerth, D. W. and Smith, R. E., "Design Factors of Gas Heating Appliances
for More Effective Use of Heat Exchange Surface," American Gas Association
Laboratories, Research Bulletin 86, January 1961.
22. Potter, J. H., and Weil, K. H., "Regenerative and Recuperative Devices for
Industrial Gas-Burning Equipment," American Gas Association Project ITU-13,
December 1958.
23. NSF/RANN Energy Abstracts, March 1974.
24. American Society of Heating, Refrigerating and Air-Conditioning Engineers,
"Papers Presented at the Symposium on Energy Conservation," Held at the
Semi-Annual Meeting of the ASHRAE, January 28 through February 1, 1973,
Chicago, Illinois, CH 73-5.
25. American Society of Heating, Refrigerating and Air-Conditioning Engineers,
"Paper Presented at the Symposium on Heat Recovery," Held at the Semi-
Annual Meeting of ASHRAE, January 24 through 28, 1971, Philadelphia, PA,
PH-71-3.
26. Tumlty, Jack E., "ASHRAE Enters Energy Conservation Crisis with Proposed
Standar 90P, 'Design and Evaluation Criteria for Energy Conservation in
New Buildings,1 An Overview," ASHRAE Journal, July 1974.
142
-------
REFERENCES (continued)
27. American Society of Heating, Refrigerating and Air-Conditioning Engineers,
"Design and Evaluation Criteria for Energy Conservation in New Buildings
(Proposed Standard 90-P) - Draft," 1974.
28. Telephone communication with D. P. Deyoe, and E-CUBE Program Bulletin,
Southern California Gas Co., April 1974.
29. Deyoe, Donald P., "Heat Recovery -, How Can the Heat Pipe Help?" ASHRAE
Journal, p. 35-38, April 1973.
30, Siedal, Marquis R., Plotkin, Steven E., and Reck, Robert O., "Energy
Conservation Strategies," Implementation Research Division, Office of
Research and Monitoring, U. S. Environmental Protection Agency, Washing-
ton, D.C., EPA-R5-73-021, July 1973.
31. 1970 U. S. Census of Housing, Structual Characteristics of the Housing
Inventory, Tables A-4, A-7, Detailed Housing Characteristics - HC(1),
U. S. Department of Commerce.
32. Gas Appliance Manufacturer Association, "Statistical Highlights - Ten
Year Summary 1963-1972, and Total Industry Factory Shipments in Units,"
January 28, 1974.
33. Gas Engineers Handbook, American Gas Association, Industrial Press Inc.,
New York, 1969.
34. 1972 ASHRAE Handbook of Fundamentals, American Society of Heating, Refrig-
erating, and Air-Conditioning Engineers Inc., New York, 1972.
35. 1972 Equipment Volume/ASHRAE Guide and Data Book, American Society of
Heating, Refrigerating and Air-Conditioning Engineers Inc., New York, 1972,
36. Strock, Clifford, and Koral, Richard L., "Handbook of Air Conditioning,
Heating, and Ventilating," Industrial Press Inc., Second Edition, 1965.
37. American Gas Association Committee on Domestic Gas Research, "Research on
Effect of Ambient Pressures in Combustion Chambers of Contemporary Appli-
ances on Primary Air Injection and Other Gas Burner Operating Conditions,"
Research Report No. 1080, June 1947.
38. Stone, R. L., "A Practical General Chimney Design Method," ASHRAE Trans-
action, Part 1, Vol. 77, pp. 91-100, 1971.
39. Dickerson, R. A., and Okuda, A. S., "Design of an Optimum Distillate Oil
Burner for Control of Pollutant Emissions," EPA-650/2-74-047, June 1974.
40. DeWerth, D. W. and DiCaprio, J. F., "Performance Tests of Residential Hot
Water Boilers Gas vs. Oil," American Gas Association, Catalog No. H00220,
January 1966.
41. Strieker, S., "Measurement of Heat Output of Residential Furnaces," ASHRAE
Transaction, Vol. 76, p. 264-278, 1970.
143
-------
REFERENCES (continued)
42. Dunning, R. L., Geary, L. C., and Trumbower, S. A., "Analysis of Relative
Efficiencies of Various Types of Heating Systems," The Energy Utilization
Project, Power Systems Planning, Westinghouse Electric Corporation, Re-
port No. PSP 10-30-70 (Revised 01-21-74).
43. "Improving the Home Oil Burner," Mechanical Engineering, p. 49, August
1974.
44. Schultz, Mort, "The New Story on Furnaces," Mechanix Illustrated, p. 122ff,
November 1973.
45. Telephone Conversation with Bob Patterson, Chevron Research Corporation,
Richmond, California, April 1974.
46. Garrivier, P., "Building Research Translation - Use of an Air-to-Air Heat
Exchanger to Recover Heat from Air Exhausted by Mechanical Ventilation,"
National Bureau of Standards, Technical Note 710-5, July 1972.
47. Thompson, R. E., Pershing, D. W., and Berkau, E. E., "Catalytic Combustion,
A Pollution-Free Means of Energy Conversion?" Environmental Protection
Agency, EPA-650/2-73-018, August 1973.
48. Roessler, W. U., et.al., "Investigation of Surface Combustion Concepts
for NOX Control in Utility Boilers and Stationary Gas Turbines," The
Aerospace Corporation, Report No. ATR-73(7286)-2, August 1973.
49. Kays, W. M., and London, A. L., "Compact Heat Exchangers," Second Edition,
McGraw Hill Book Co., New York, 1964.
50. McAdams, William H., "Heat Transmission," Third Edition, McGraw Hill Book
Co., Inc., New York, 1954.
51, "Cost of Gas," Pacific Gas and Electric Co. Newsletter, August 1974.
52. Telephone conversation with Bert Gunghry, Fuel Oil and Heat Magazine,
September 13, 1974.
53. Vent-0-Matic Draft Control Bulletin, AIA File No. 30-0-4, Save Fuel Corp-
oration, Tunica, Miss., 1969.
54. Grant, Eugene L., and Ireson, W. G., "Principles of Engineering Economy,"
Fourth Edition, The Ronald Press Company, New York, 1960.
55. Telephone discussion with Mrs. Charles Woolfolk, Save Fuel Corporation,
Distributors of Vent-O-Matic Draft Control, August 1974.
56. Dunning, R. L., and Geary, L. C., "Analysis of the Efficiency and Cost of
Equivalent Residential Comfort - Conditioning Systems," The Energy Utili-
zation Project, Power Systems Planning, Westinghouse Electric Corporation,
Report #PSP2-10-74.
57. Hall, R. E., Wasser, J. H. and Berkau, E. E., "A Study of Air Pollutant
Emissions from Residential Heating Systems," NTIS PB229667, January 1974.
144
-------
REFERENCES (continued)
58. Heller, A. N., "Impact of Changing Patterns of Energy Use on Community
Air Quality," presented at the 57th Annual APCA Meeting, June 1964.
59. Barrett, R. E., et.al., "Field Investigation of Emissions from Combustion
Equipment for Space Heating," prepared for EPA and API by Battelle, Colum-
bus Laboratories, EPA-R2-73-084a, June 1973.
60. Hall, R. E., et.al., "Status of EPA's Combustion Research Program for
Residential Heating Equipment," presented at the 67th APCA Annual Meeting,
June 1974.
61. Ehrenfeld, J. R., et.al., "Systematic Study of Air Pollution from Inter-
mediate-Size Fossil-Fuel Combustion Equipment," prepared for EPA by
Walden Research Corp., July 1971.
62. Kane, J. M., "Fabric Collectors for Collection of Particulates," presented
at the ASHRAE Semi-Annual Meeting, January 1972.
63. Telephone interview of Mr. R. Swezey, Air Filter Corp., South San Francisco,
California, June 7, 1974.
64. Telephone interview of representative of American Air Filter, Louisville,
Kentucky, May 12, 1974.
65. Bonn, D. E., "Wet Collectors for Collection of Particulates," presented
at the ASHRAE Semi-Annual Meeting, January 1972.
66. Communique from Bahco, Inc., Sweden, May 5, 1974.
67. Eckert, J. S., "The Use of Packed Beds for Wet Removal of Particulates
from a Gas Stream," presented at the ASHRAE Semi-Annual Meeting, January
1972.
68. Eckert, J. S., "Wet Packed Gas Scrubbers," presented at the ASHRAE Semi-
Annual Meeting, January 1973.
69. Enneking, J. C., "Control of Vapor Emissions by Adsorption," presented at
the ASHRAE Semi-Annual Meeting, January 1973.
70. Barnebey, H. L., "Activated Charcoal Adsorption in Combination with Other
Purification Methods," presented at the ASHRAE Semi-Annual Meeting, January
1973.
71. Telephone interview with Mr. D. Matefy, Combustion Equipment Assn., Inc.,
May 21, 1974.
72. Telephone interview of representative of Trion, Inc., Sanford NC, May 15,
1974.
73. Telephone interview of representative of Universal Air Precipitator Corp.,
Monroeville PA, May 12, 1974.
74. Hardison, L. C., "Electrostatic Precipitators for Industrial Gas Cleaning,"
presented at the ASHRAE Semi-Annual Meeting, January 1972.
145
-------
REFERENCES (concluded)
75. Telephone interview of Mr. R. Leach, The Ducon Corp. (Division of Milcropul)
Mineola NY, May 15, 1974.
76. Brookman, G. T., and Kalika, P. W., "Measuring the Environmental Impact of
Domestic Gas-Fired Heating Systems," presented at the 67th APCA Annual
Meeting, June 1974.
77. Brown, R. A., Mason, H. B., and Schreiber, R. J., "Systems Analysis Re-
quirements for Nitrogen Oxide Control of Stationary Sources, " Environ-
mental Protection Agency Report No. EPA- - -, 1974.
78. Fraas, Arthur P. , and Ozisik, M. Necati, "Heat Exchanger Design," John
Wiley and Sons, Inc., New York, 1965.
146
-------
APPENDIX A
A-l
-------
FLUE LOSS CHARTS
Figure A-l presents a flue loss nomogram from the AGA Laboraties for
butane, propane; coke oven and natural gases. A typical line is shown for
natural gas at 60 percent excess air, 20 percent flue losses and 335°F tem-
perature difference or about 405°F exit temperature.
Figure A-2 shows a similar nomograph from the Gas Engineers Handbook
for determining a gas appliance performance. Table A-l lists the procedures
for using this chart. A typical example might be to determine the overal heat
transfer coefficient knowing the C0_ level, temperature rise, and heat exchanger
loading (the fourth problem in the table). The applicable appliance classes
referred to in Table A-l are as follows:
1. Forced air furnances:
Parallel flow} updraft
Counterflow >with downdraft
Crossflow ) steel or cast iron
2. Gravity furnaces; floor furnaces; room, space, and recessed heaters
3. Water heaters and boilers
4. Deep fat fryers
5. Gas range ovens (for input - C0_ relationships and flue losses)
Figure A-3 shows similar curves for heat loss in flue gas for fuel oils.
To use this chart either enter with the excess air or CO- level and proceed to
find the other using the excess air curve. From that intersection move ver-
tically upward or downward on the excess air line to the flue temperature line.
Then proceed horizontally to read the flue loss.
A-2
-------
I
LO
1 —
_
_
UJ
2 '*5 ~"
QL
O
QZ
Q. Z-
Q -
Z
< J
uj :
< 3-
00 j
co :
UJ 4-
co
CD
UJ 3-j
_j I
6—
Z :
^" ~
~ 7~_
O :
a—
6 -
^ J
10-
—
12—
I4J
%co.
UJ 600-
UJ Z
< 2
f- o
o o: 500—
m o_
— 600
— 500 — ;
— 400 — £
— 3OO — ;
-
— 200 ~ _I
_ —
— 100 —
_ —
_ —
_
— 50 ~~
-50 400—
r40 350 -j
r30 300—
'- 25
250-
-20
200—
— 15 "
- 12 150-
%FLUE LOSS :
BUTANE AND PROPANE
_
— o —
% EXCESS AIR IN FLUE GASES
100—
Z
III *
^ ^J
_ o g
UJ ^
o <
O 2
— ~"~^
- 35 soo
. O
• 2
i
- ^^ ~
- rf 40—
r o E
L _J "^^ 30—
. u. \. :
^\^^ _i ;
~ ^ f*^^ •
- z z atv^
- UJ
- £
- u.
• u.
o
UJ 13-
• or
. -3
H
-50 S00_
•
j — ^
—40 400
•
: 300_
-30
: uj ~
UJ ~
-20 O
x^ o -
- ^\^^ — 2>
^\ ~~-
^•v. —
^^^ —
— ^Xv~-—
- 15 _ 30
— —
- 2 %FLUE LOSS
- UJ _ -
0.
- "S. v -
UJ o
H —
% EXCESS AIR
IN FLUE GASES
— 1
-
-
UJ
^5
UJ
iC
o
rj
r2 o
z
- 2.5 _|
<
: t
: <
L Z
— 4 UJ
CO
: °
r5 uj
" f it
— 6 U.
r z
~7
: 0
-8 0
,«
E_ °"
— 10
— 12
%co.
— 1
Figure A-l. Alignment Chart for Calculation of Flue Losses for Butane, Propane,
and Coke Oven and Natural Gases. (Adapted from A.G.A. Laboratories'
Flue Loss Charts.)
-------
E, COMBUSTION EFFICIENCY, %, OR (100% —FLUE LOSSES, %)
01
o
a>
ui
oo
o
CD
MODULATION LINE
s>
ro
•
— • ->• cr>
in v>
— '"O
• CU S»
S T3
c+TJ
— '
— h — '•
T CU
O 13
3 n
n>
3>^5
• o
I— 3
CU Cu
o- 3
o o
T O>
CU
<-t o
o zr
-s cu
(T> ft-
trt •
O) O
l/l Cu
Cu
CD
c o
— • cr
""•* r+
Cu
OI 3
oo ns
- o.
1 ' ' ' ' 1 ' ' '
FLUE GAS TEMPERATURE _§
RISE ABOVE AMBIENT, °F J^
i i i i .j i i i i j "Jr**"^ ! '
~~ I***! ro
J- ro
o o
EXCESS AIR,% -o 8 o
(READ ON C02 LINE) £"' ' '
C02,% -^~ . ? , '
C1 1 I t . 1 , 1 i
WEIGHT OF FLUE GASES, o ' i
LBS PER 1000 BTU OF °» °
HEAT INPUT
Oft C? A OJ N
o o o o o
1 ! 1 1 1 1 1
ii i i i i i | i i ' i i i i < i i ^^
ro w
o,*g 85 g3
g S g g o o ° ? i £3)
o o°__£ 1— ' ' ^
>-J— l— INDEX LINE /j)
i t 1 | 1 ( i 1 j i 1 < 1 | 1 1 1 1 j 1 I 1 1 | 1 1 1 1 | V — /
o* ^ tji
_ rO CM -Ck O> OD O
mooO o oo o oo
00° o oo o oo
III 1 III 1 1 I 1 1 1 1 @
f i T i t T T i T— co2,% @
1 i 1 , 1 i 1 i 1 i 1 i t i , 1 i i I i 1 . i i I ] £ W
J. -1 J. i 1 1 i ' 1 i III (Q]
ro * b> oo f° .ol * o> oa ^^
o ob ob
o
55o.*o.~y « @
HEATING ELEMENT LOADING, IOOO BTU/(SQ FT OF AREA)(HR)
ALTERNATE USES : PER CENT
INPUT-C02 PIVOT LINE
t i i i i i i i i
OR MULTIPLES OF HEAT INPUT
T,i T , i ©
' ' ' ' 1 'l I1 1 1 1 ' ' ' ' ' /c>
' ro *o> oa i. (o
o o ^^
ALTITUDE CORRECTION, THOUSANDS OF FEET
-
ro o OD
I J I I I
fO
en Xk oi en
I,,,,I....I,.,,!,., .1, . , . I , ,
in
I
U, OVERALL HEAT TRANSFER COEFFICIENT, BTU/(HR)(SQ FT)(F)
(BASED ON UNFINNED SURFACE)
-------
TABLE A-l.
APPLICATIONS OF THE GAS APPLIANCE PERFORMANCE CHART (see Figure A-P)
Problems
involving
Efficiency, COi. flue
cas temperature
Efficiency. COi, over-
all heat transfer co-
efficient, area, heat
input
Input and CO: (no
changes in appli-
ance geometry)
Efficiency variations
for excess air
changes at constant
heat input
Effect of altitude
changes on heat In-
put and CO: in flue
products
Weight of flue
products
Effect of modulated
heat input on appli-
ance efficiency
(from 50 to 125% of
normal heat input)
Temperature of fluo
gases after dilution
at draft hood
Known factots
Efficiency (1).
CO, (6)
Flue gas temp
rise (3). CO: (6)
Efficiency (1). flue
gas temp rise (3)
CO, = 8% (6). flue
gas temp rise =
300 F (3). loading
= 3000 Btu/sq ft-
hr(8)
Estimated U = 6.0
(11), input =
72,000 Btu/hr,
area = 4 sq ft,
loading = 72,000/
4 = 18,000(8),
operating CO, =
7% (6)
CO, = 8.5% (6).
input = 80,000
Btu/hr. i.e., 8.0
on (8) scale
Input = 60.000
Btu/hr (8). CO, =
9% (6). B = 70%
(1)
Input = 50,000
Btu/hr. i.e. ,5.0
on(8)scale,atsea
level (10). CO,
value not reqd.
CO, = 7.5% (6) at
sea level (10)
COj— 7. 5% (6). in-
put = 50.000 Btu/
hr. I.e. .5.0 on (S)'
scale, at sea level
(10)
Input = 150.000
Btu/hr. CO, =
7.9% (6)
Input = 170.000
8tu/hr. i.e., 17 on
(8) scale, CO, =
7% (S). efficiency
- 80% (1)
Flue gas temp rise
= 450-F (3) CO, =
8% (6) (before
dilution)
Flue gas temp =
800 Fat 8.0% COi
(6) In recessed
heater. Dilution
air is heated to
300 F, CO, after
dilution is2. 5%
(6)'
Find
Flue gas temp
rise (3)
Combustion
efficiency (1)
CO, (6)
U: overall heat
transfer co-
efficient (11)
£: predicted
combustion
efficiency (1)
CO, (6) at: (a)
100,000 Input, (b)
50,000 input
Efficiency at 6%
CO.and 60,000
Btu/hr Input
Input at 6000 ft
(10)' to obtain
same CO, as that
at sea level
(without altering
appliance)
CO, at same In-
put and 4000 ft
alt.(10)(without
altering appli-
ance)
CO, at 30,000
Btu/hr input.
i.e.,3.0on(()'
scale, and 5000
ft alt. (10)'
Flue gas rate
Efficiency(l)'at
120.000 Btu/hr,
I.e.. 12 on (8)'
scale (without
altering appli-
ance)
Efficiency (!)• at
220,000 Btu/hr.
i.e.. 22 on (8)'
scale
Temperature at
3% CO: (6)' after
dilution with
room air
Gas temperature
downstream of
draft hood
Procedure
(l)(6)-»)
(3)(6)-(l)
(1) (3)-(6)
(6>(3>-(4)(3.27)
(4)(8)-(ll)
(11)(8)-»(4)(1.82)
(4)(6)-(l)
(6>(8)->(9)(1.47)
(»)(8)a-(6)a
<9>(8)J~(6)6
(1) <«>-<«> (2.34)
(«)(6)'-.(l)'
(10)(»y-*(6> (5.8)
(6)(10)'-*(8)'
(10)(6>-K8)(6.5)
'-(6)'
(a) CO, (6)' at 5000 ft and
50,000 input:
(10)(6)-(8)(6.5)
(«)(10)'-(6)'
(9.4)
(6)— (7) (1.12 lb/1000 Btu)
(6)(8)-(9) (0.78)
(»(«)'-'(ar-(S)(1.9)
(9) (8)'—
w
(1) (6)- (2) (2.2)
(2,(V)
For precise work,
the modulation
point should be
found by operat-
ingattwo differ-
ent heat inputs
Assume no heat
loss at draft hood:
thus, E is con-
stant
Temp rise entering hood Dilution air tern-
- 800 - 300 or 500'F (3) peraturels
above dilution airtemp treated as ambl-
(6)(3)-»(l) (76.0) entairtempera-
|| ture for this
(1) (6)'—(3)' calculation
U — 2.75
Btu/hr-sqft-°F
E=52.5%
CO,: (a) 11%,
(b) 5.4%
B = 61%
Input o 39,000
Btu/hr
CO, = 9.0%
CO, =-5.5%
(1.12X115.000)/
1000 = 129 Ib/hr
B= 78.3%
£ = 81.3%
Temp = 190'F
above room
Temp = 175'F
above 300, or
475 F
Appli-
cable
appli-
ance
1. 2 3,
4. 5
1. 2. 3, 4
1,2,3,
4.5
1 2 3, 4
1, 2 3.
4.5
1. 2. 3,
4,5
1 2, 3, 4
I, 2. 3, 4
Appli-
cable
fuel
N. T. M
N, T. M
N, T. M
C. B, P
N, T, M
N. T. M
C, B, P
N
N, T, M
N, T, M
C, B. P
* See text.
t Code for fuel gases: N — natural; T •» manufactured, 525 Btu, 0.42 cp gr; M — mixture, natural and manufactured; C — coke oven; B —
butane and butane-air; P — propane and propane-air.
t This rule as subsequently revised states that appliances do not have to be derated at elevations up to 2000 ft; for elevations above 2000 tf.
ratings should be reduced at the rate of 4 per cent for each 1000 ft above sea level.
A-5
-------
FUEL OIL
NO. 2
c ess % SOT/,
H l?.6 O'W'tsr, 0.?
.Gross I9.50O Btuper Lb
Net 19,4IO Btu per Lb
Lbperlbof fuel
Flaf Gas • 131 ?3 Cu ft (tVet)per Lb of '
Ultimate C0f - /5.3Z%
Stack toss Percentage Based,
..1.4-
0 20 40 60 SO /OO IZQ 140 160
ISO ZOO Z2Q 240 $60 Z60 300 320 340 3AO 38O 4OO
Percent, Excess Air
FUEL OIL
NO. 6
C 66.6% 5
H 10.? OfJVfAst> t.O
Heat Vbtve. Cross /8.3OO Bttt per Lb
Btu
Air etotf -I3&4 Lb per Lb of Fuel
- IS8-4& CuFt.(rVet)perLbofFt,t.
^Ultimate C0r -
Stack Loss Percentage Based on
0 !0 40 O> SO 100 120 HO HO
ISO lOO ??0 140
Percent Etctss
Figure A-3. Heat Loss in Flue Gas-Fuel Oils
From Strock & Koral (36) Chapter
6, Fuels & Combustion
A-6
-------
DOLIN HEAT TRANSFER ANALYSIS
Specifications:
Tubes: 52 - 3/8 OD x 20 ga. Bare Steel Tubes
Spacing: 5/8 x 5/8 Triangular Pitch
5 Tube High x 11 Tubes wide
Overall Length: 10-3/8" long
Width: Tubes +2" each side for bypass
Blower: Grainger 2C610:Nominal 140 CFM
Analysis:
k 0.625 -H = xnd
J T
).
4-
0.625 = x d
0.375
x^ = 0.625/0.375 = 1.667
x = 0.625/0.375 = 1.667
Outside Heat Transfer Coefficient
From Kays and London (Reference 53) p. 127
NST Npr2/3 = 0-38NR~°'* f = 0.40NR-°'18
Assume the flue gases are from oil fired furnace using 60 percent excess air.
Then,
Mf = 2.11 Ibs/min
A-7
-------
Calculate open areari
10.375
Open 2 "
Tubes
7.25
Open
2"
Side Area *-'- 40 in2
• «•«
Free Flow Area = (10.375) (7.250) (0.4) - 30.09
Now assume the flow is proportional to the open area:
Then,
Total Open Area = 30.09 + 40 = 70.09
' 2.11 = 0.906 Ibs/min
G = 144 =4.33 lbs/min-ft
Heat Transfer Area = 635.58 in2 = 4.414 ft2
DU = 0.0547 ft
NR = 245
N
ST
= °'38
- 0.0421 = (0.7)
2/3
Cp = 0.25
h = 3.468 Btu/hr-ft2°F
A-8
-------
Inside Heat Transfer Coefficient
Figure A-4 shows the fan curve and the system curve for the air flow
through the tubes. This reveals that the actual flow is about 61 CFM. Using
this number the following calculations were made to determine the inside heat
transfer coefficient:
M = (61) (0.075) = 4.575 Ibs/min
A = "(0.305)' 452) „ Q_264
c 4 144
G = 04 '0527654 = 173.3 Ibs/min-ft
= (0.305) (173. 3)
(12) (1.2 x 10~5)60
N = 0.022(6117.5) °'8 (0.8073) = 18.998
U
. _ (18.998) (0.015)12 _
n 07205 11.
Overall Heat Transfer Coefficient
Then the overall heat transfer coefficient:
u 3.468
U * 2.5 Btu/hr-ft2°F
Then to determine the overall efficiency using the Kays and London (53) tech-
nique :
NTU - AU
min
= (0.9058) (0.25) = 0.226 =
C = (4.575) (0.24) = 1.098
C
A-9
-------
100
120
140
Flow (cfm)
Figure A-4. Blower Performance Curve
(Crainger 2C610 Blower)
-------
C . /C = 0.206
mm max
= (2.5)(4.414)
(0.226)(60)
NTU = 0.8138
e ~
= 1 - e-°'812'
e
= 0
.5568
Table A-2 summarizes the flue temperature heat absorbed and percent
savings of the total furnace input. The energy consumed by the blower has
been subtracted from the total. Figure A-5 shows this data in graphical form.
A-ll
-------
TABLE A-2
DOLIN HEAT RECLAIMER PERFORMANCE
Let's assume T = 60°F
in
Case
q(Btu/hr)
"M
net
% Input
500
600
700
800
255
299
344
388
395
470
547
623
110
122
133
145
3322
4077
4827
5586
-273
-273
-273
-273
3049
3804
4554
5313
3.05
3.80
4.55
5.31
f
Due to
Blower Motor
Definitions
= Cooling air temp in (°F)
= Cooling air temp out (°F)
= Flue gas temp in (°F)
= Flue gas temp out which goes through tube bundle (°F)
= Combined flue gas temperature out
net
% Input =
Heat recovered by device
Energy used to drive air blower
Net heat saved q . = q -
qnet/100,000 Btu/hr
A-12
-------
6000
5000
0)
c
cr
4000
3000
Furnace Size: 100,000 Btu/hr
Excess Air: 60% (Oil Fired)
Cool ing Air Temp: 60°F
Cooling Air Flow: 61 scfm*
500
600 ' 700
Flue Inlet Temp (°F)
800
See attached curve of resulting operating point of Blower
Figure A-5. Dolin Heat Reclaimer Performance
-------
HEAT TRANSFER ANALYSIS
The performance of noncondensible heat exchangers was determined using
the technique of London and Kays (49). A simple computer program was written
in order to facilitate rapid screening of potential designs. A listing of
this program together with an input format is included in this appendix. The
program is applicable to plate-fin and fin tube designs in single pass or
multipass crossflow arrangements. In addition C . /C as defined below is
min max
assumed to be much less than 0.25.
Condensible heat exchangers were analyzed using a combination of hand
calculation based on a technique by McAdams (50) and the above computer pro-
gram to determine the performance of the noncondensible portion as well as
the pressure drop.
Noncondensible - NTU Heat Exchanger Analysis
The efficiency of a crossflow heat exchanger with C . /C « 0.25 is
mm max
approximately equal to the following expression:
, -NTU
e - 1 - e
where
AU
NTU =
min
C . = W C for either the hot or cold side.
U = overall conductance fo heat transfer
1 a 1
= n u h A /A. k A /A, nET
o,h n V h c h o,c c
A = surface area on which U is based (ft2)
n = fin efficiency
A-14
-------
The effectiveness is related to the temperatures by the following expression:
e = cc,out
C(tc,
G2
29C Vl
IV 4-1
\ i\ • J-
c
-.-ft-
max min( h,in c,in) min( h,in ~ c,in)
The reader is referred to Kays and London (49) for specific definition of the
above nomenclature. The computer program calculates the overall conductance
a/
from given performance data for a specific surface (correlations of St Pr 3
vs. Reynolds number) , the flows, temperatures, and overall configuration.
In addition the pressure drop is calculated from the following expression:
4P'
Entrance Flow Core Exit
Effect Acceleration Friction Effect
The friction factor versus Reynolds Number data for the surface must be pro-
vided to the program. Table A-3 lists the required input information and
Figure A-6 shows a typical output listing. Figure A-7 is a listing of the
program.
Condensible Heat Exchanger Performance
The condensing heat exchangers were analyzed using the Log-Mean-Temper-
ature Difference (LMTD) approach. The principal expression relating heat
transfer to the LMTD is as follows:
q = U A F (LMTD)
where
F = correction factor for crossflow and/or multipass arrangement
(see Figure H4.2 of Fraas and Ozisik (78))
U = overall conductance for heat transfer (provides for a con-
densing coefficient)
A = surface area on which U is based
At - AtT
LMTD =
At /AtT
O J
A-15
-------
TABLE A-3
INPUT DATA FOR PERF
NAMELIST/HX
HXH
HXD
HXL
HX length perpendicular to flow
HX length parallel to flow
HX length direction of cells
inches
inches
HXH
HXL
cs •
cw
Cell size or tube diam. or tube +
Fin Diam.
Cell width or fin length on finned
tube
cW
inches
inches
DA/
NFC
FT
NS
XHR
AFAT
XPTC
ACTOVC
Number of fins per cell
Fin thickness
Number of segments per side #tubes
Hydralic radius
Fin area/total area
Plate thickness
Total heat transfer area/volume
between plates - cold side
N.A. to tubes
inches
feet
inches
Ft2/Ft3
A-16
-------
TABLE A-3 (continued)
AHTOVH
XKM
IDIAG
NTUBE
SIG
COND
Total heat transfer are/volume
between plates - hot side
Thermal conductivity of HX
material
Flag for diagnostic output
1 = Diagnostic output
0 = No diagnostic output
Total number of tube in bank and
# tubes in first bank facing gas
Free flow area/frontal area
Thermal conductivity of air
Ft2/Ft3
Btu/hr-ft-°F
NAMELIST/FLOW
XMDOT
TIH
TIC
Mass flow rate
Inlet temp of hot side
Inlet temp of cold side
Lb/min
°F
°F
NAMELIST/HXTYPE
I FLAG
DIAMTI
DIAMTO
DTH
DTC
0 - Plain plate fin surface
1 - tube bank
Tube diameter (inside) - only used
if IFLAG = 1
Tube diameter - (outside)
Distance between tube center - bank
side
Distance between tube centers - tube
side
inches
inches
inches
inches
NAMELIST/CHECK
RHO
XMLL
CP
XPR
Density - value for air and gas
Viscosity
Heat capacity
Prandtl Number
Lb/Ft3
Lb/Ft-sec
Btu/lb-°F
NAMELIST/HC
IA
IB
1 - air side HX characteristic table
2 - gas side HX table
(This enables user to determine effect
of changing fluid flowing thru each
side of HX.)
A-17
-------
TABLE A-3 (concluded)
NAMELIST/REN
REYN
NPT
Reynolds Number - ascending order
Number of Reynolds Number pts
NAMELIST/HT2
HTRC1 j factor - HX side 1 - match to corresponding
Reynolds Number (j = (h/GC ) Npr/3)
NAMELIST/ERIC1
FRF1 f: friction factor -HX side 2
NAMELIST/HT2
NAMELIST/ERIC3
NAMELIST/CONFIG
ICONFG
Same as above for HX side 2
Number of configurations to be run
Notes: Tube Bank Crossflow HX
1. Tube bank size input must be the open area of the first pass only.
2. For each configuration each NAMELIST having changed values must be
input again
NAMELIST 1
NAMELIST 2
NAMELIST 3
NAMELIST 2
Config. 1
Config. 2 - uses namelist values from
Config. 1 for NAMELIST 1 and 3 and new
values input in NAMELIST 2.
a. The read statement for each NAMELIST with changed values must be
inside the 5000 DO loop - see program listing line 35, 3b.
NAMELIST 1
NAMELIST 2
NAMELIST 3
NAMELIST 4
Do 5000
NAMELIST 5
NAMELIST 6
These will be reread for configuration 2 through
N with new values.
3. The NAMELIST input must be in the same order as the read statements -
program lines 25 through 36.
A-18
-------
DLS,289777,1»50 6 AUG 74 12156123 PAGE
HEAT
~"HEAT
HEAT
EXCHANGER LENGTH
EXCHANGER LENGTH
EXCHANGER LENGTH
HEAT EXCHANGER PERFORMANCE CODE
CONFIGURATION 5
• PARALLEL TO FLOW - INCHES
. PERPENDICULAR TO FLOW «
INCHES
- DIRECTION OF CELLS • INCHES
SINGLE CELL HEIGHT
SINCLE CELL WIDTH -
FLO* PATE • LB/HIN
NUMBER HX SEGMENTS
REYNOLDS HEAT TR. HEAT TRANSFER
NUMBER COEF AREA
(BTU/FT**2 (FT**2)
hR F)
COLO
SIOE
HOT
SIOE
2616. 8531 11.
1234,5896 10.
6940 id, 4537
«731 8.9677
U NTU EFFICIENCY
(8TU/FT**2
HR F)
• INCHES
INCHES
PRESSURE
DROP
(IN H20)
.1226
1.7211
QROT
CBTU/HR)
COLE SIDE I-OT SIOE
1.173 15.000
15.000 1.173
7.137 7.137
.195 .16fl
.544 .249
75.000 2.070
9 9
INLET OUTLET
TEMP TFHP
(F) CF)
1«0."0000 146.5342
400.0000 181.4632
6,6109 1.8359 ,8405 7056.9897
TERMS I AND 3 OF 1/U EQUATION
TERM 1 TEPM 3
.09640 ,05487
EFFICIENCY COEFFICIENT
149.4011
Figure A-6. Typical Output Listing
-------
DL3,289777.1,50
• FOR PERF.PERF
DATE, TIME, LEVEL OF OUTPUT ELEMENT! 26 AUG 74 14100(00)
FORTRAN VI ISO VERSION 2.9
28 AUG 70
28 AUG 70
14|00|43 PAGF
OOlOfllOO.321
MAIN PROGRAM
STORAGE USED (BLOCK, NAME, LENGTH)
0001 *COOe 041267
0000 *OATA 00)332
0002 *BLANK o.ioooo
EXTERNAL REFERENCES (BLOCK, NAME)
0003 T8LP
0004 NRNL«
OOOS NEXP6I
0006 TANH
0007 EXP
0010 NWDUI
0011 NI02S
0012 N3TOPJ
STORAGE
0001
0000
.„ 0000
i 0001
£ 0001
0001
0001
0000
0000
0000
0000
0000
0000
0000
0000
0000
0000
oooo
OQOO
0000
oooo
oooo
oooo
oooo
oooo
oooo
R
R
R
H
R
R
R
R
R
I
I
I
R
R
R
R
R
R
R
ASSIGNMENT FUR VARIABLES
000332
001023
001177
001137
000677
000450
000543
000415
000371
000067
000430
000363
000105
000055
000255
000161
000411
000400
000021
000002
000073
000421
000121
000031
000033
000065
10L
1460F
1600F
2000L
337G
59L
65L
AC
AHTOVH
C
CMIN
D
DP
ETAF
FP.F1
HTRCI
I
IFLAG
NFC
NTU
RHO
TERM1
TO
XG
XMOOT
XPTC
OOOO
0001
OOOO
0001
0001
0001
0001
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
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oooo
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oooo
oooo
oooo
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0000
oooo
R
R
R
p
R
R
R
R
R
I
I
I
I
R
R
R
R
R
R
(BLOCK, TYPE, RELATIVE
000661
000366
001226
000602
001066
000522
000763
000417
OOOllS
000025
000375
000'433
000404
000113
000313
000217
000405
000437
000410
000351
000374
000422
000436
000037
000041
000035
1000F
1SL
1610F
304G
417G
60L
80L
ACTOAH
AREA
CA
COND
OCOEF
OTC
ETAO
FRF2
HTHC2
IA
MN
NHXCON
NTUBE
SIG
TERM2
TOC
XHR
XMU
XRC
OOOO
0001
OOOO
0001
0001
0001
0001
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
oooo
LOCATION, NAME)
R
R
R
R
R
R
R
R
R
I
R
I
I
R
R
R
R
R
000657
001175
001247
000620
000404
000167
000767
000370
000071
000426
000047
000111
000403
000361
000023
000005
000406
000000
000407
000413
000103
OOOU7
000434
000372
000416
1200F
150L
1620F
310L
SOL
600L
SSL
ACTOVC
AREAA
CAIR
CP
OELTAP
OTH
F
FT
HXD
IB
H8PV
NPT
NUSLT
SIGMA
TI
TOM
XKM
XPAS3
OOOO
oooo
0001
oom
ooot
0001
0001
OOOO R
OOOO R
OOOO R
OOOO R
oooo
oooo
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oooo
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oooo
oooo
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000663
001072
000120
000625
000422
000220
000272
000061
000420
000427
oonoii
000401
000365
000015
000045
000003
000367
000425
000027
000435
000077
000377
000424
000057
000051
tsooF
1510F
I65G
520L
55L
610L
<»L
AFAT
AVGAlN
CGAS
CS
DIAMTI
E
FA
HTC
HXH
ICCNFG
Kl
NS
OOOT
SPECVL
TIC
U
XL
XPR
OOOO
0001
0001
0001
0001
0001
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000760
00121?
000130
000631
000446
000210
R 000355
R 000414
R 000357
R 000431
R 000017
R 000402
R 000432
R 000107
R 000043
R 000007
I 000373
I 000013
I 000412
R 000123
R 000353
R 000376
R 000423
R 000053
R 000063
160L
173G
330L
58L
620L
A
AH
e
CMAX
cw
DIAHTC
EFF
FF
HTN
HXL
IDIAC
NC
NTP
REVN
TA
TIM
UINV
XM
XPT
Figure A-7. Program PERF Listing
-------
OLJ,289777,1,50
28 *UG 74 14IOOI4S PAGE
00101
0010]
ootoi
00101
0010]
0010)
00104
00105
00106
00107
00110
00110
00111
00112
0011)
OOHfi
OOltS
00116
00117
00120
00121
00122
00122
00132
00122
0012]
00126
001)1
001)4
001)7
00142
00145
ootso
0015)
00156
00161
00164
00167
00167
00167
00167
00172
00175
00177
00200
00201
40202
0020)
00205
00206
00207
00210
00211
00212
0021)
00214
00215
00216
00217
00220
1*
2*
)*
4*
5*
6*
7*
8*
9*
10*
11*
12*
D*
14*
15*
16*
17*
18*
19*
20*
21*
22*
2)*
24*
25*
26*
27*
28*
29*
)0*
31*
32*
))*
)4*
)5*
)6*
37*
38*
39*
40*
41*
42*
43*
44*
45*
46*
47*
48*
49*
50*
51*
52*
53*
54*
55*
56*
57*
58*
59*
60*
C
c
C
c
c
c
RC*L H3PV.NTU
DIMENSION HXHC2)fHXOC2>,HXU2),C3<2),NCC2),FA(2),CW<2),NFC(2).
1FT(2>,CA(2),N3{2).XGC2),XMDOT<2),XREC2J,XHR{2),XMU(2).'HTN<2),
2HTC(a),CP(2),XPR{2),XMe2),ETAFt2),XU(2),AFAT(2).XPT<2).XPTC(2).
)CC2),AREAA<2),RMPC2.2),SPECVL<2,2),3IGMA(2),«8PVC2).OP<2).FF(2).
4DElT*P(2)iETAO(2)rAReA(2)fTI(2),TO(2)
DIMENSION REYNC30>,HTRClC)0>rHTRC2()0),FRFl()0),FRF2{)0)
DIMENSION NTUBE(2J,TA(2J
DIMENSION AC2),BC2),FC2>,DC2),E(2)
NAME11ST/CONFIG/ICONF6
NAMEUIST/HX/C3.CW,NFe,FTfXHR,AFAT,XPTC,ACTOVC,AHTOVH,XKM,TOIAG,
* SIG.COND
NAMEUI3T/VAR/HXH,MXO,HXU»N3,NTUBE
NAMEl.IST/Fl.OW/XMDOT,TIH,TIC
NAMELI3T/HXTYP£/IFUAG,t>IAMTI*DUrtTO,DTH,OTC
NAMEUI3T/CHECK/RHO»XMUfCP»XPR
NAMEI.I3T/HC/IA,I8
NAMELI3T/REN/REYN,NPT
NAMEUI3T/HT1/M7RC1
NAMELI3T/FRIC1/FRF1
NAMEUI3T/HT2/HTRC2
NAMELI3T/FRIC2/FRF2
READ INPUT
REAOC5,HX)
REAO(S, CONFIG)
READ(5»HXTYPE)
REAOC5, CHECK)
READ(5,HC)
READCS.REN)
READ(5,HTl)
READ(5,Pf»Ipl)
REAO(5,HT2)
READ(5,FRIC2)
REAO(5,FLO«)
00 5009 NHXCON*1»ICONPG
REAOtS.VAR)
DETERMINE HAS3 FLOW INTO HEAT EXCHANGER
DO 100 I«l,2
IF(IFLAG.EOil) GO TO 600
NC(I)»HXH(I)/C3(I)
FA(tiiCH(Ij*C3(I)-NFCtI)*CW(I)*FT(I)
CACI)«FA(I)*NC(I)*N3(I)
GO TO 610
600 IF(I,EQ.2) GO TO 620
NC(I>«NTUaE(I)
FA(I)«HXUCIJ*HXH(I)
TA(TJ«(),141S«(01AMTI«*2))/41
CA(I)«NC(I)*TA(I)
GO TO 610
620 NC(I)«NTUBE(I)
N3CI)»NCCI)
FA(I)«HXL{I)*HXH(I)
CA(t)iFA(I)*3IG
610 XG(I)i(XMDOT(I)*144,)/CA(I)
XREa)«(XHR(I)*XG(I))/(XMU(I)*60.)
Figure A-7. Continued
-------
DLS,289777,1.50
28 AUG lit 11100143 PACE
00220
00220
OR220
00221
00223
0022!
00226
00227
00230
00232
Ort234
0023!
0023T
002*0
00211
00241
00201
00241
00242
00244
00246
00247
00250
00250
00250
00250
00251
00252
002S4
00255
00256
00257
00260
00261
00262
00264
00266
00267
00270
00271
00272
00273
00274
00275
00276
00277
00300
00301
00302
0(1302
00302
00302
00303
00306
00307
00311
00312
00313
00316
00317
61*
62*
63*
64*
65*
66*
67*
6A*
69*
70*
71*
72*
73*
74*
75*
76*
77*
78*
79*
ao*
81*
62*
83*
84*
85*
86*
87*
88*
89*
90*
91*
92*
93*
94*
95*
96*
97*
98*
99*
100*
101*
102*
103*
104*
105*
106*
107*
108*
109*
110*
111*
112*
113*
114*
115*
116*
117*
118*
119*
120*
C
C
C
C
C
C
C
C
C
C
C
C
TABLE UOOK-UP
IFCI.E0.2) CO TO 10
IF(tF|_AG.E0.1)GO TO 9
CALL TBLPCXRe(IA),REYN,HTN(IAJ,HTRCl,NTP,OJ
CALL TBUP(XRE(IAJ,REYN,FF(IA),FHFl»NTP,l)
60 TO 10
9 IF(X«EC1).LT.2000.) FF(l)«6«i/XReCl)
IF(xRECl).GT.aoOOf) *f Cl >«. 184/CxRE < 1 )**.2J
NU3LT«,022*CXREC1)**.8>*CXPR(1>**,667)
10 IF(I.EQ.l) 60 TO 15
CALL T8LPCXR£CIBJ,REYN,HTNCIB),HTRC2,NTPfO>
CALL TaLP(XRECIBi,REYN,FF(IB),FRF2,NTP,l)
IS CONTINUE
DETERMINE HEAT TRANSFER COEFFICIENT
IFCIFLAG.EQ.O) GO TO 50
IF(I.EQ.2)GQ TO SO
HTCCl)»(NU3LT*CGNO*12.)/niAMTI
GO TO 55
50 HTC(I)«CHTNC I) *XGC1)*CP(I)*60.)/XPR (!>*«. 667
DETERMINE U
55 XM(I)«((2.*HTC(I)*12.)/(XKM*FTCnn**,5
IFCIFLAG.EO.O 60 TO 58
GO TI; 59
58 XLCn«((COTHfDTC)/2.)-DIAMTO)/(a,*12.)
59 ETAF(Ij»TANH{XMf I j*XL(I)l/CXMCI)*XLtI))
ETAOCI)«l.-AFATCI)*(l.-£TAF(n>
XPT(I)»XPTC(I)/12.
100 CONTIHOE
IF(IFLAG.EO.l) GO TO 60
AH»A^TOVH*N3C2)«CHXH(2)*HXDC2)*CWC2))/1728.
ACBACTOVC.NSf l)*tHXM(l)*HXD(l)*CW(l) )/1728.
GO TU 65
60 AC»3. 1415*01 AMTO*HXO(1)*NC{ I)/ 144.
XPA83«HXL(1)/HXL(2)
AHaAHTQVH*(HXH(a)*HXD(2)*HXL(2)*XPA33)/l728.
65 CONTINUE
ACTQ»H«AC/AH
AVGA4«(AH*AC)/2.
TERMl«
-------
D 1.3,289777,1.50
28 AUG 74 14IOOIU3 PAGE
00320
00321
00322
00323
00323
00323
00323
00324
00325
00326
00326
00326
00326
00327
00330
00331
00331
00331
00331
00332
00333
00334
00335
00336
00341
00343
00341
00346
00350
00351
00352
00353
00354
00355
00356
00357
00360
00361
00362
00363
00364
00365
00367
00370
00371
00372
00373
00374
00374
00374
00374
00375
00377
00377
00415
00416
00421
00421
00416
00436
121*
122*
123*
124*
125*
126*
127*
128*
129*
130*
131*
132*
133*
134*
135*
136*
137*
138*
139*
140*
141*
142*
143*
ia*CTIH-TOH)*60.
TOC«TIC+(QDOT/CXMOOT(1)*CP(1)*60.J)
C
C DETERMINE PRESSURE DROP
C
SPECVL(t,lj»13.33
3PECVLCl,2)«13,6S
SPECVL(2,l)»21.74
3PECVL(2,2)»14,08
DO 430 MN»1,2
IFCIFL*S.E0.1.AND,MN.IO.I) XHR C 1 j«2.*XHR C 1 )
AREA* MN)»HXD(MN)*4./( XHR (MN)*12,>
IFUPHG.eo.l.'AND.MN.EQ.l) XHRC 1 )»XHR( 1 )/2.
IFCIPLAG.EQ.l) GO TO 80
SIGMA (MN)»N3(MN)*NC(MN)*FA(MN)/(HXH(MN)*H XL (f*N) )
GO TO 65
80 3IGM(l)«CA(l)/FACl)
SIGM»(2)«3IG
85 CONTINUE
HSPv(MN)»(3PECVU(MN,l)»SPECVL(MN,2))/21
ACMN)«(CXG(MN)**2)*3PECV(.CMN,l))/(2,*32 .2*3600,)
B(MN)*(l,+SIGMA(MN))
F(MNJ«(CSPECVL(MN,2))/CSP£CVLCMN, t)))-l.
D(MN)»(FF(MN)*AREAA(MK.))
ECMN)«M3PV(MN)/SPECVUMN»1)
DP(MOaA(MN)*((P (MN) *F(MN)) + {D(MN)*£(MN)))
OELTAP(MN)»DP(MN)/C 144.*, 036125)
420 CONTINUE
AREA(1)«AC
AREA(2)aAH
TI ( 1 )«TIC
TI(2)»TIH
TO(1)»TOC
TO(2)«TOH
C
C PRINT OUTPUT
C
IF(IUIAG,EQ.O)GO TO 2000
KRITE(6,1200)AH,AC,U,EFF,TOH,TOC, ACTOAM,CMIN,CMAX,OCOT
*,AVGAW,NTU
1200 FORMATC1H1.13F9.3)
00 1100 Ul,2
HRITE«t,'1000)HXHCI),HXI)CI),HXL(I)> FA ( I ) , CA ( I ) , XG ( I ) , XRE ( I) .
*HTC ( I ) , OP U ) , DEIT AP ( I ) , NC < I )
WRITE (6, 1000) XM(n,XL(I),ETAF(I),ETAO(I),AREAA(I),SIGMA(!),
*M3PV(IJ,HTN(I),FF(I)
Figure A-7. Continued
-------
013,289777,1,50
28 AtG 71 1HOOI43 PACE
00151
00460
00161
00163
00164
00175
00175
00175
00175
00175
00175
00175
00175
00176
00500
00512
00512
00512
00512
00513
00511
00526
00526
00526
00526
OP 526
00527
00530
00530
00546
00516
00546
.K, 00516
i 00546
£00546
00547
00555
00555
00556
00562
00562
00563
00566
00567
00571
00572
181*
182*
183*
184*
185*
186*
187*
188*
189*
190*
I'l*
192*
193*
194*
195*
196*
197*
198*
199*
200*
201*
202*
203*
204*
205*
206*
207*
208*
209*
210*
211*
212*
213*
214*
215*
216*
217*
218*
219*
220*
221*
222*
223*
224*
225*
226*
WRITE (6, 1000) A(I),BCI),F(I),OCn»E(I>
1000 FORMAT(10F10.4,I5J
1100 CONTINUE
2000 CONTINUE
WRITE (6, 1100) NHXCaN,HXDOK3m,C3C2),C»'Cl>,CW(2J.XMDOT(l),XMOOT(2),NSm,N'SC2>
1«60 FORMATC52X, 'TUBE DIAMETER - INCHES ', 9X, F9 .3, //52X,
1 'TUBEtFlN OUSTER - INCHES '. 19X, F9 .3, X/52X,
2 'FIN LENGTH - INCHES',12X,F9.3,5X,F9,3,//,52X,
3 'FLO- RATE » L8/MIN',13X,F9,3,5X,F9,3,//,52X,
a 'NtJKBER HX TUBES' ,2lX, 12, 12X, 12, ///)
160 CONTINUE
WRITE(6,1510)XRE(1) , HTC(1),AREA(1>,DELTAP(1),TICO,TO<1 1,
*XREC-n,HTCC2),AREAC2),OELTAP<2),TIC2),TO(2)
1510 FlORM4T(Jl<, 'REYNOLDS', 2X, IHEAT TR. ' , IX, ' HEAT TRANSFER ' ,5X,
l'PRE3SUSE',3X, 'INLET'.SX. 'OUTLET ',/, 32X,
2'NUM1ER',5X, 'COEF' ,10X,iAREA',llX, 'DROP' ,6X,'TEHPI,7X,'TE^P',/10X,
3'(ST.J/FT**2',5X, ' (FT**2)',9X, ' (IN H20) ',1X, ' (F) >,7X, ' (F j ' , 5X , /1?X ,
1'HR F)' ,//22X, 'COLDI,3X,2F10,1,5X,F10.1,5X,3F10.1,/22X, 'SIPF',//,
522X, 'HaT',1X,2F10,1,5X,F10.1,5X,3F10.1,/,22X, 'SIDE'.///)
WRITE (6,1 60 0)U,NTU,EFF»QDOT
1600 FORMATfJIX, 'U',8X, ' NTU ' , IX, ' EFFIC IENCY ' , 3X , ' ODOT ' , /,'flOX .
1 ' (RTU/FT**2',21X, ' (8TO/HR) < , /,12X, 'HR F)',//,38X,3F10.1,2X,F10.1)
WRITE(6,1610)TER«1,TERM2
1610 FORMATC///,16X, "TERMS 1 AND 3 OF 1/U EQUATION ', //52X, ' TERf 1',
*5X, 'TERM 3I,//,18X,F10.5,2X,F10.5J
WRITE(6,1620) DCOEF
1620 FORMAT(///,50X, IEFFICIENCY COEFFICIENT ' ,//,6lX, F10 .«)
5000 CONTINUE
BOO STOP
* CROSS REFERENCE BY SEQUENCE NUMBER *
A 1
AC I
ACTCAHl
ACTQVCl
AFAT |
AH I
AHTCVHl
AREA I
AREAA 1
0106
0267
0275
0110
0103
0266
0110
0103
0103
0356
0271
0377
0267
0110
0273
0266
0367
0343
0363
0275
0260
J275
0273
0370
(1361
0451
0276
0276
0530
0136
0300 0367 0377
0300 0301 0324 0370 0377
Figure A-7. Continued
-------
Ot»,2MT7T,l/50
• ran TSL>."THP „ : ... •
DATE. TIHI, LEVEL 'OF OUTfUT ELEMENT! 28 AUS 74 14lOOCOOi
FORTRAN VI 180 VERSION I,'*
•18 AUG 74
18 AUS 74
14100141 PAGE
ootooioi;784
tt
SUBROUTINE TBL> ENTRY POINT OOOtOi
STORAGE USED (BLOCK, NAME, LENGTH)
0001
0000
0002
•CODE
• DATA
•BLANK
000123
000024
000000
EXTERNAL REFERENCES (BLOCK, NAME)
0003 NERR3S
STORAGE ASSIGNMENT FOR VARIABLES (BLOCK. TYPE, RELATIVE LOCATION, NAME)
0001 00005* 20L
0001 000033 1L
0000 I 000000 I
0001 000041 2L
0000 R 000001 RX
0001 000022 ••••
0101
0101
010*
0101
0101
on*
0101
0101
0121
0103
0107
0104
0111
0120
0107
0121
0112
0121
0120
0113 0120 0121
Figure A-7. Continued
-------
DL3,289777,I,50
28 AUS 74 IfllOeHJ PAGE
• ELT RNDK,1,740828, SOaOO
000001
OR0002
000003
000004
000005
000006
000007
oooooe
000009
000010
000011
000012
000013
000014
000015
000016
ooooir
000018
000019
000020
000031
SHT1
SHX CS«,377, .1675, CW», 47, ,2U9,NFC«3, 2, FT», 006,. 006, XHR«. 0301 «, .009196,
AFAT«.719,.769,XPTC»,00*,,006f ACTOVC«188, » »HTQVH«393. .XKf«120 ..
IOIAG«1 SEND
SCONFIG ICONFG«2 SEND
JHXTYPE IFLAG«O SEND
SCHECK HHO»,075,,0733,.0«6,,071,XMU».000013,.OOOOl5S,CP«.2a,.26.
XPH«.72,,7 SEND
SHC IA«1,I8«2 SEND
S4EN RSVK»300., 400., 300., 600., 800,, 1000., 1200., 1500., 3000., 3000., 4000.,
9000. ,6000., 7000. ,8000, ,9000,, 10000. ,NPT«17 S^ND
HTi*Cl«. 01 3,, Oil,, 0095,, 0085,, 0073.. 0065,. 0061,. 0057,. 0055.. 0052.
,0048,. 0045, ,0043,. 004, ,00397 ,.0038,, 0037 SEND
'P.Fl«.057,.047,,037,,03,.023,.019,.017,,0!«6,,01J..OH..009Y8,
,00913, .0087, ,0082, .0081, .0078,. 0076 SEND
SHT2 HTHC3". 0122,. 0098,, 0083,. 0073, .0059, .005, . 0044 , .0038. .0033, .0032,
,0033,. 0032,. 00322,. 0032,. 0031,. 003,. 00298 SEND
SFRIC3 "Fa«.05J5,.0411,.OJ36,.0385,.033,.018l,.OlS9,.qi3B,.01145.
,0096,. 0089,. 0036,, 0082,, 0078, .0076, .0073, ,"0072 SENP
SFLOW XHDOT«75.,2.07,TIH«S1)0.,T1C»70. SEND
SVAR HXHI20.0, 1.508, HXDil. 508, 20.0, HXL'IS.0, 15., NSB18, 18 SEND
SVAR HXH«201(2,33,HXO«2,33,20.,HXL«10,, 10,,NS«13,13 SEND
END CUR, ISO VERSION 2.14
Figure A-7. Concluded
-------
At = temperature difference between streams at the inlet (greatest
temperature difference)
AtT = temperature difference between streams at the exit (least
la
temperature difference)
The overall conductance is calculated as before for the noncondensible
portion and a heat transfer area determined to achieve an effectiveness to
reach the dewpoint.
The condensing heat transfer coefficient was estimated using a proce-
dure outlined by McAdams (50) in Chapter 13, Part IV. The situtation is one
of a condensible in an otherwise noncondensing medium. This produces a heat
transfer coefficient different from either a pure condensing stream or pure
forced convection. The procedure is as follows:
A partial resistance 1/U1 is calculated which consists of only
the resistances on the cold side, the dirt deposit, the tube
wall and the condensate film:
i_ + i + _L
V /A k A /A h
w v w w v m
The overall heat transferred balance from the cold side to the
gas and condensing stream is then
q" = uMt. - t ) = hQ (t - t.) + A[KG(P - P.)]
sensible heat latent heat
where
hr = forced convection heat transfer coefficient on the gas side
(Btu/hr-ft2°F)
A = latent heat of condensation Btu/lbm
Kr = mass transfer coefficient through gas film (Ibs vapor con-
densed/hr-ft2)
tT = temperature of cold stream
Lt
t = vapor temperature
A-27
-------
t. = interface, temperature between condensed layer and gas
P. = vapor pressure of water at t.
P = vapor pressure of water at t
One assumes a value of t. and substitutes the vapor pressure and
repeats the procedure until the equation balances. The total area
required is then determined by graphically or otherwise integrating
the following expression:
:i - tL)
This must be done stepwise proceeding through the heat exchanger.
A rough guess (and this is what was done) on the resulting over-
all heat transfer coefficient to any location may be found by
using the following expression:
h =
By looking at this value of h at the inlet and outlet conditions
an average value may be chosen to estimate the overall area re-
quired for the condensing portion of the exchanger. Mass trans-
coefficients can be determined from the expression:
KGPnm f Hv r3 O._023
where
pv
n * Schmidt Number * 0.6 for water vapor in air
pv v
P = log mean vapor pressure of the noncondensible portion
at t. and t
ND = Reynolds number of the vapor
K
Pressure drops were calculated using the computer program as before
but using the total heat transfer volume.
A-28
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing/
1. REPORT NO.
EPA- 600/2 -76-097
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Feasibility of a Heat and Emission Loss Prevention
System for Area Source Furnaces
6. REPORT DATE
April 1976
6. PERFORMING ORGANIZATION CODE
Project 7089
7. AUTHOR(S)
R.A. Brown, C.B. Moyer, andR.J. Schreiber
8. PERFORMING ORGANIZATION REPORT NO.
FINAL REPORT 74-117
9. PERFORMING OR3ANI2ATION NAME AND ADDRESS
Aerotherm Acurex Corporation
485 Clyde Avenue
Mountain View, California 94042
10. PROGRAM ELEMENT NO.
1AB013; ROAP 21ADD-042
11. CONTRACT/GRANT NO.
68-02-1318, Task 5
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Task Final; 2-10/74
14. SPONSORING AGENCY CODE
EPA-ORD
is. SUPPLEMENTARY NOTES Task officer for this report is W. B. Steen, Mail Drop 61, Ext
2825.
16. A6STRACTThe reporf gives results of a. brief study to determine the feasibility of
candidate concepts for simultaneous heat and air pollutant recovery from the exhaust
of domestic-size furnaces. Among the concepts investigated were improved heat
exchanger design, vent dampers and heat pipes, and post-combustion emission
control devices such as filters and wet scrubbers.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Heat Recovery
Combustion
Furnaces
Flue Gases
Exhaust Systems
Heat Exchangers
Vents
Damping
Pipes (Tubes)
Filters
Scrubbers
Air Pollution Control
Stationary Sources
Domestic Heating
Vent Dampers
Scrubbers
13B
20M,13A
2 IB
13K
07A
8. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport/
Unclassified
21. NO. OF PAGES
183
2O. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
F-l
------- |