vvEPA
         United States
         Environmental Protection
         Agency
          Industrial Environmental Research
          Laboratory
          Research Triangle Park NC 27711
EPA-600/7-80-099
May 1980
A Demonstration of
Beneficial Uses of Warm
Water from  Condensers
of Electric Generating
Plants

Interagency
Energy/Environment
R&D Program  Report

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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 nine series. These nine broad cate-
 gories were established to facilitate further development and application of en-
 vironmental technology. Elimination  of  traditional grouping was consciously
 planned to foster technology transfer and a maximum interface in related fields.
 The nine series are:

     1. Environmental Health Effects Research

     2. Environmental Protection Technology

     3. Ecological Research

     4. Environmental Monitoring

     5. Socioeconomic Environmental Studies

    6. Scientific and Technical Assessment Reports (STAR)

    7. Interagency  Energy-Environment Research and Development

    8. "Special" Reports

    9. Miscellaneous Reports

This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series.  Reports m this series result from the
effort funded  under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the  Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects;  assessments of, and development of, control technologies for  energy
systems; and integrated assessments of a wide'range of energy-related environ-
mental issues.
                        EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for  publication. Approval does not signify that the contents necessarily reflect
the  views and policies of the Government, 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-600/7-80-099

                                               May 1980
A  Demonstration  of  Beneficial Uses
  of Warm Water from Condensers
     of  Electric  Generating Plants
                          by
             LL Boyd (U. of MM), G.C. Ashley, J.S. Hietala,
                R.V. Stansfield, and T.R.C. Tonkinson

                 Northern States Power Company
                      414 Nicollet Mall
                 Minneapolis, Minnesota 55401
                     Grant No. S-803770
                  Program Element No. EHE624
                EPA Project Officer: Theodore G. Brna

             Industrial Environmental Research Laboratory
           Office of Environmental Engineering and Technology
                 Research Triangle Park, NC 27711
                       Prepared for

             U.S. ENVIRONMENTAL PROTECTION AGENCY
                Office of Research and Development
                    Washington, DC 20460

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                                  PREFACE


     Northern States Power Company has been involved with the development of
beneficial uses of power plant waste heat since 1970.  As construction of
the two-unit coal-fired Sherburne County (Sherco) station progressed, accom-
panied by an intensified energy crisis, waste heat utilization appeared to
be economically feasible.  With its closed-cycle cooling system and adequate
condenser outlet temperatures, Sherco was selected as the site for a warm
water greenhouse heating demonstration.

     The University of Minnesota Agricultural Experiment Station and the
United States Environmental Protection Agency joined forces with NSP in
developing a program.  The resulting Sherco Greenhouse Project is an excellent
example of cooperation by an educational institution, a government agency,
and private industry in meeting the challenge of a national energy problem.
                                     n

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                               CONTENTS
Preface	   ii
Abstract	   iv
Figures 	    v
Tables	   vi
Abbreviations 	  vii
Acknowledgments 	 viii
Introduction  	    1
Conclusions and Recommendations 	    2
Description of Facilities 	    3
  1.  Structural Facilities 	    3
  2.  Air Heating System  	    5
  3.  Backup Heating System 	    5
  4.  Soil Heating System	    7
  5.  Cooling/Ventilation System   	    7
  6.  Greenhouse Water Circulation System  	    8
  7.  Control System	   10
  8.  Data Collection System	   11
  9.  Heating System Performance and Operating Experience  	   11
 10.  Severe Cold Weather Performance Data	   12
 11.  Electric Energy Consumption  	   23
 12.  Waste Heat Availability  . 	   32
 13.  Operating Problems  	   42
 14.  Greenhouse System Operation  	   43
General Horticultural  Considerations  	   44
  1.  Soil   	   44
  2.  Irrigation	   44
  3.  Fertilization	   45
  4.  Pest Control	   45
  5.  Harvesting and Marketing	   46
  6.  Detailed Cultural Methods 	   46
        Tomatoes	   47
        Snapdragons	   49
        Roses	   49
        Lettuce	   49
        Qeraniums	   49
        Containerized  Tree  Seedlings   	   50
        Nursery Stock  	    51
Economic  Feasibility   	    52
Heat  Delivery  Cost  and Pricing Concepts	    5^
Heat  Exchange  System  Cost	    55
Operating Cost Comparison to  Conventional  Systems 	    56
Appendices
  A.  Background	    %
  B.  Pilot Project	      	    ^
                                   ill

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                                  FIGURES
Number                                                                  Page

  1      Heating and Cooling System Schematic 	   4
  2      Trane Air Handler  	   6
  3      Modine Unit Heater 	   6
  4      Soil  Heating System Headers	f  .  .   8
  5      Cooling Water Circulation  System Schematic  	   9
  6      Unit I Gross Electrical  Output and Condenser
           Outlet Water Temperature January 9,  1977  	   13
  7      Heating System Performance January 9,  1977  	   14
  8      Wind Speed January 9,  1977	16
  9      Solar Radiation January  9, 1977  	   17
 10      Heating System Performance January 9,  1978  	   18
 11      Heating System Performance January 10,  1978  	   19
 12      Heating System Performance February 2,  1978  	   20
 13      Air Heating System Performance January  9, 1977  	   21
 14      Soil  Heating System Performance January 9,  1977   	   22
 15      Typical Warm Water Temperatures  	   24
 16      Typical Greenhouse Air Temperature 	   25
 17      Condenser Outlet Water Temperature Distribution January, 1978   26
 18      Average Greenhouse Air Temperature Distribution January, 1978   27
 19      Typical Warm Water Temperature Variation With Unit  Load  ...   28
 20      Monthly Electric Power Consumption of Heating Fans  and Pumps  .   30
 21      Monthly Capacity Factors of Greenhouse  Heating System Units   .   31
 22      Monthly Electric Power Consumption of Greenhouse  Boilers
           During Unit I Outages	35
 23      Pipeline Losses Between  Unit 1 Condenser and Greenhouse
           January 8, 1978	37
 24      Pipeline Losses Between  Unit II Condenser and Greenhouse
           January 10, 1978	38
 25      Connection at Cooling  Tower
 26      Warm Water Distribution  System Schematic 	   40
 27      Sherco Power Plant and Greenhouse Complex   	   64
                                     iv

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                                   TABLES
Number                                                                  Page

  1     Sherco Greenhouse Electrical Power Consumption 	   32
  2     Warm Water Availability  	   33
  3     Summary of Warm Water Availability and Temperature 	   34
  4     Cropping Chronology  	   47
  5     Yields of Marketable No. 1 and No. 2 Tomatoes	   47
  6     Yield Vs. Density for Tropic Tomato - Spring 1977  	   48
  7     Growing to Flowering Time - Geraniums	   50
  8     Crop Yields	   50
  9     Waste Heat System - Materials Cost Summary 	   55
 10     Comparative Operating Costs of Waste Heat Versus
          Conventional Heating  	   57

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                      LIST  OF  ABBREVIATIONS AND SYMBOLS
 ABBREVIATIONS

 British  thermal  unit
 British  thermal  units  per hour
 British  units  per  hour per square foot
 British  thermal  units  per pound
 centimeter
 cubic feet per minute
 cubic meters per second
 degrees Celsius
 degrees  Fahrenheit
 foot
 foot-Candles
 gallon
 gallons  per min
 gallons per min
 gallons per square foot
 gigajoule (one billion joules)
 gram
 hectare
 horsepower
 hours
 inch
 kilogram
 kilogram per cubic meter
 kilojoule per  kilogram
 kilowatt
 kilowatt-hour
 liters per second
 liters per square meter
megawatt
megawatt-hours
meter
million British thermal units
ounce
ounces per cubic feet
 parts per million
 pound
quart
 square foot
square meter

SYMBOLS

 calcium
 calcium carbonate
 carbon dioxide
magnesium
 temperature differential
Btu
Btu/hr
Btu/hr-ft2
Btu/lb
cm
ft3/nrin
m3/s
°C
°F
ft
ft-C
gal
gal/min
gpm
gal/ft2
GJ
gm
ha
hp
hrs
in
kg  a
kg/m3
KJ/kg
kw
kwh
1/s
1/m2
MW
MWH
m
MBtu
oz
oz/ft3
ppm
Ib
qt
ft2
m2
Ca
CaC03
C02
Mg
AT
                                     VI

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                               ACKNOWLEDGMENTS


     The authors gratefully acknowledge the contributions  and  support  given
to the Project by the following individuals and organizations:

Project Employees:

  Patricia Adamson, Assistant Horticulturist
  Roberta Brehmer, Assistant Horticulturist
  Ron Svehla, Assistant Horticulturist

University of Minnesota Staff:

  Keith Huston, Director Agricultural Experiment Station
  Evan R. All red, Agricultural Engineering
  Alvin A. Aim, Forest Resources
  Donald G. Baker, Soil Science
  George R. Blake, Soil Science
  David W. Davis, Horticulture Science
  Arnold M. Flikke, Agricultural Engineering
  James V. Groth, Plant Pathology
  Kenneth A. Jordan, Agricultural Engineering
  Sagar V. Krupa, Plant Pathology
  Frank Lang, Electronics Technician
  Harold Pellet, Horticulture Science
  Francis L. Pfleger, Plant Pathology
  Paul E. Read, Horticulture Science
  Elwin L. Stewart, Plant Pathology
  James B. Swan, Soil Science
  Richard E. Widmer, Horticulture Science
  Harold F. Wilkins, Horticulture Science

Commercial Greenhouse Operators:

  Gordon Bailey, Bailey Nurseries
  Leonard Busch, Len Busch Greenhouse
  Al Hermes, Hermes Floral
  Don Hermes', Roseville Greenhouse-Becker
  Jim Hermes, Hermes Floral
  Tom Hermes, Roseville Greenhouse-Becker
  Tom Lange, VEG,  Inc.
  Don Rosacker, Hans Rosacker  Floral
  Richard Young, Northgro, Inc.
  Richard Zelinka,  Forjay, Inc.

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Northern States Power Company:

  D. W. Angland, Executive Vice President
  E. C. Glass, Director, Planning & Research
  L. C. Weber, Manager of Research
  Pat Gordon, Plant Manager, Sherco
  Wayne Kaplan, Communications Representative

Environmental Protection Agency:

  James Chasse
  Alden Christiansen
                                   vili

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                                INTRODUCTION
     In July 1978, the total electric generating capability of United States
power plants was 540,000 megawatts (MW).1  Assuming that there will  be a 3-4%
compound annual growth rate, a modest forecast by most utility standards,
energy availability by the late 1990's must be doubled.  This means that
before the year 2000, the nation's power demands will  be more than  one
million MW.

     Rapidly increasing demand for electric power requires that each day for
the next 20 years, an average of 74 MW of electric power generation will be
placed in service in this nation.  A high proportion,  80%, of the added
generating facilities will be thermal plants, with large volumes of warm
water discharged from the condensers.

     Using present technology, generating plants are only 35-40% efficient.
Putting it another way, nearly two-thirds of the energy required for plant
operation is not converted to electricity.  Most of the unused thermal energy
is rejected by the cooling system and is called waste heat, although the
rejected heat is a consequence of the second law of thermodynamics  and is not
willful waste.

     All steam-electric generating stations require huge quantities of cool-
ing water to dissipate waste heat.  To protect the environment, most future
power plants will be required to install a closed-cycle system of cooling,
utilizing cooling towers or cooling ponds.  Temperatures of circulating
cooling water leaving the condenser in a closed-cycle design are likely to
be in the 24°-49°C (75°-120°F) range, considerably higher than the condenser
discharge of "once-through" cooling plants.  A closed-cycle 1000 MW plant
requires cooling water circulated at the rate of 25,240 1/s (400,000 gpm),
rejecting nearly 52.8 X 106 GO (50 X 1012 MBtu) of waste heat each year.

     A truly energy conscious society must recognize the tremendous waste of
energy this represents on a national scale.  New ways to recapture waste
heat should' be explored to make the best possible use of non-renewable
resources:  coal, oil, natural gas, and uranium.
 National  Electric  Reliability  Council  - July,  1978, Review

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                       CONCLUSIONS AND RECOWENDATIONS


     The Sherco Greenhouse project has satisfactorily demonstrated that
power plant condenser discharge water, with a minimum temperature of 29.4°C
(85°F), can be used to supply the total heating requirements of greenhouses
in a northern climate.  The demonstration has proven the technological and
economic feasibility of this application of power plant waste heat.

     At the same time, it is acknowledged that:  (1) the capital investment
in a warm water heating system is slightly higher than the investment in a
conventional heating system and (2) electric power costs will be greater
with a warm water heating system than with a conventional heating system.

     If the results of this project are to be successfully applied at other
power plant sites, it is recommended that:

     (1)  Reliability of warm water service be considered by selecting
          power plants with two or more generating units.

     (2)  The individual greenhouse owners provide an adequate backup
          heating system in the event of a warm water supply outage.

     (3)  The area at the power plant reserved for greenhouses be as
          close as practicable to the source of warm water.

     (4)  The greenhouse structure should employ energy saving features
          such as a double-layer roof and sidewalls.

     Northern States Power Company is presently leasing land to private
greenhouse operators for the purpose of building waste heat greenhouses.  It
is intended that the greenhouse owners build and manage their own structures
and equipment.  The Company will provide a supply of warm water at a fair
and reasonable rate reflecting:  (1) the capital investment required to
deliver the warm water, (2) the operating and maintenance expense connected
with the pipeline, and (3) the electric energy necessary to pump the warm
water from the power plant to the greenhouse complex.

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                          DESCRIPTION OF FACILITIES
STRUCTURAL FACILITIES
     The Sherco Greenhouse is  a conventional  arch  frame,  gutter-connected
style.  The 14 modules, or bays, are each 5.2 m (17  ft) wide  by  29.3  m
(96 ft) long and represent a covered surface  area  of 0.21 ha  (0.53  acre).
The gutter clearance height is 2.4 m (8 ft) with the longitudinal axes of
the bays oriented north-south.  This type of  greenhouse was chosen  for the
demonstration project primarily because of the lower initial  capital  cost
and because of the wide acceptance of the structural type among  greenhouse
operators and growers.

     The roof covering of the greenhouse is a double layer, air-inflated
ultraviolet-resistant polyethylene.  The double layer of  polyethylene was
determined to be the most viable roof covering because of lower  initial
capital cost, high popularity with growers and primarily  because of the
higher resistance to heat transfer.  Replacement of  the roof  covering was
performed on an annual basis mainly due to the nature of  the  project  with
regard to potential failure during the winter heating season.  The  only
problems experienced with the polyethylene roof covering  were slight  and were
associated with damage due to ice formation coupled  with  high winds during
winter sleet storms.

     The east and west side walls and south end wall are  covered with an
outside layer of reinforced corrugated fiberglass  panels  and  an inside
layer of polyethylene.  The north end wall is covered with an outside and
inside layer of polyethylene.   The lower portion of  the  polyethylene on the
north wall is raised to act as an outside air intake for  the  evaporative  pad
cooling system as shown in Figure 1.

     The greenhouse crops and mechanical equipment were  arranged to provide
north-south bench and row orientation.  East-west  main walkway access was
provided on the south end of the greenhouse and on the north  end under the
structures used to support the heat exchanger units.

     A crop support system was added as a retrofit design, independent of the
basic greenhouse structure.  The rose support system consists of three layers
of galvanized welded wire fabric which extends the full  25.9  m (85  ft) length
of each bench.  The crop support system for the tomato plants utilizes a wood
member frame for supporting overhead horizontal steel pipes.   The tomato
plants were supported with nylon twine.

     The headhouse adjoining the greenhouse is a 12.2 m  (40 ft) by 18.3 m

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OUTSIDE AIR

   FOR
                           WARM WATER
                             OUT
           INSIDE RETURN AIR
                 f R
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WINTER HEATING
                          WARM  WATER
                              IN
                RECIRCULATIN'
                WATER
                EVAPORATIVE
                   COOLER
                              COOL AND HUMIDIFIED

                              AIR  FOR SUMMER

                              COOLING
             WARM WATER
             INLET HEADER
                               UNDERSOIL  HEATING  PIPE&v
 WARM WATER
OUTLET HEADER
                              Figure  1  Heating and Cooling  System Schematic

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(60 ft) steel frame building.   The headhouse accommodates  space  for  a  pro-
duction work area, a boiler room, a data acquisition  and control  room,  an
office and restroom, a data acquisition and control  room,  an office  and
restroom area, a walk-in cooler and a mechanically vented  chemical  storage
cabinet.  The headhouse acts as a central facility for all  horticultural and
mechanical system operations.

AIR HEATING SYSTEM

     The heating system employed in the Sherco greenhouse  consists  of  an air
heating system and a soil heating system.  Warm water is circulated  through
an underground piping grid to provide crop root zone  temperature control and
also through finned-tube, forced air heat exchangers.

     The air heating system was designed to provide all of the make-up heat
requirement of 586 KW (2.0 X 105 Btu/hr) at the design conditions of -34.4°C
(-30°F) ambient and 10°C (50°F) greenhouse air dry bulb temperature.  The
water to air heat exchange is accomplished by use of commercially packaged
fan/finned-tube heat exchanger units.

     Twelve of the 14 greenhouse bays are equipped with 2.24 KW  (3 hp) centri-
fugal air handlers in combination with draw-through finned coils as  shown  in
Figures 1 and 2.  The rated heat transfer capability of the coils is 44.5  KW
(1.52 X 105 Btu/hr) with 29.4°C (85°F) entering water and 10°C (50°F)  enter-
ing air conditions.  At the design water flow rate of 1.87 1/s (29.6 gal/min)
and the design air flow rate of 3304 1/s (7000 ft3/min), the coil outlet
conditions of 21.2°C (70°F) air and 23.9°C) (75°F) water temperatures  are
experienced.  Heated air is uniformly distributed by overhead 0.76 m (30 in)
diameter perforated polyethylene ducts which extend the full length of the
bay.

     The two center bays of the greenhouse are equipped with a horizontal
discharge (non-ducted) unit heater in each end, oriented to discharge air
toward the opposite end heater.  These unit heaters, as shown in Figure 3,
have circumferential finned-tube coils with 746 W (1 hp) propeller fans.
At the design air flow rate of 3260 1/s  (6900 ft3/min) and water flow rate of
1.0 1/s (16 gal/min), these units will effect a heat transfer rate of 17.6 KW
(6.0 X 105 Btu/hr) from 29.4°C (85°F) entering water to 10°C (50°F)  entering
air.  The unit heaters were installed to permit comparative indications of
the economic or technical performance benefits inherent in either type of
heat exchanger unit.

BACKUP HEATING SYSTEMS

     The greenhouse is equipped with an  alarm system which monitors three
parameters critical to the environment control system operation.  Project
personnel are notified of alarm conditions caused by greenhouse air tempera-
tures below  10°C  (50°F)  (in the event of mechanical equipment failure), by
supply water temperatures below 23.9°C (75°F) (in the event of an unscheduled
power plant  outage) or by an electric power interruption.

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  Figure 2  Trane Air Handler
Figure 3  Modine Unit Heaters

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     Since the greenhouse electric power is not supplied directly by  the
Sherco plant, two 390 KW (1.28 X 106 Btu/hr) electric hot water boilers
serve as a standby heat source in the event of simultaneous,  two-unit plant
outage.  These boilers were used during the 1975-76 heating season to pro-
vide heating by simulating circulating water temperatures, before the first
generating unit was operating commercially.

     In the event of an electric power interruption during the heating
season, an emergency heating system is utilized.   A 10 KW propane-fueled
electric generator provides emergency power for lights and for portable
propane heater operation.  Six 103 KW (3.5 X 105  Btu/hr), propane-fired,
forced-air heaters are deployed in the greenhouse to provide  heat until
normal electric service conditions are restored.   In both electric power
interruptions experienced during the past three heating seasons, scant use
of the emergency system was necessary because of  prompt restoration of normal
electric power service.

SOIL HEATING SYSTEM

     The soil heating system was installed primarily to provide crop root
zone temperature control capability to enhance plant response.  While soil
heating does provide a small portion of the makeup heat requirements, the
air heating system is designed for the total heating required because of  the
inherent slow thermal response time of the soil heating system.

     The installed soil heating system (Figure 4) consists of 2.54 cm (1  in)
diameter polyethylene pipes spaced 0.61 m (24 in) on centers  and buried
approximately 30.5 cm (12 in) below grade.  Each  bay of the greenhouse con-
tains a grid of 8 pipes and the 14 grids are header-connected to form two
systems of seven grids each.  The soil heating system is supplied circulation
water in parallel with the air heating units (Figure 4) on a demand basis.

     The soil heating design water temperature differential is 5.6°C (10°F)
with 29.4°C (85°F) supply water at the design flow rate of 0.063 1/s (1 gal/
min) per pipe.  The temperature differential estimate  of 5.6°C (10°F) was
based on a 10°C (50°F) soil surface temperature and a 15.6°C  (60°F) root  zone
temperature.

COOLING/VENTILATION SYSTEM

     The greenhouse cooling system, as shown schematically in Figure 1,
functions fndependently of the heating system.  The conventional evaporative
cooling system utilized consists of a 0.91 m (36 in) high cellulose pad
mounted vertically to extend the length of the north wall of  the greenhouse.
Potable water is distributed and recirculated through the pads at a rate of
7.57 1/s (120 gal/min).  Air is drawn through the wetted pads by fourteen
0.91 m  (36 in) propeller type exhaust fans, with one fan located  in the
south end of each bay.

     The total design cooling air flow rate is 9.2 X 104 1/s  (1.95 X 105 ft3/
min) or 6.6 X 103 1/s  (13,900 ft3/min) per bay.

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                   Figure  4   Soil  Heating  System  Headers
     All fans and the evaporative pad system are operated automatically with
the outside air intake of the pad system fully open during periods when
cooling is required.  During the moderate temperature transition periods from
heating to cooling, ventilation with preheating is provided by operating the
centrifugal air handlers with the outside air intake open as shown in
Figure 1.  During periods with ambient temperature below freezing, the re-
quired minimum ventilation is provided by manual operation of exhaust fans
drawing outside air through two 0.6 m (24 in) wall louvers located in the
two center bays of the greenhouse.  As discussed more completely in the
control system description, ventilation for humidity control within the
greenhouse is provided as a manual function.

GREENHOUSE WATER CIRCULATION SYSTEM

     As shown schematically in Figure 5, water circulation through the green-
house system is provided by primary circulation pumps.   From the main supply
pipeline, water is pumped through the greenhouse heat exchangers by four
3.73 KW (5 tip) pumps, each of which is capable of circulating 9.47 1/s
(150 gal/min).  Two pumps operate in parallel per zone on a demand basis, as
explained in the control system description.  The soil  heating system is
equipped with one 0.75 KW (1 hp) secondary booster pump per zone, which
operates on a demand basis.

                                      8

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V
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                           Figure 5  Cooling Water  Circulation  System Schematic

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     The design water flow rate of 25.6 1/s (406 gal/min)  for air heating
and 7.1 1/s (112 gal/min) for soil heating, or a combined  total  circulation
flow rate of 32.7 1/s (518 gal/min), are based on the maximum design water
temperature differential of 5.6°C (10°F).

CONTROL SYSTEM

     The greenhouse environmental control function is predicated upon  simple
on-off thermostat control, with dry bulb temperature being the only auto-
matically controlled variable.

     Each of the 14 greenhouse bays are equipped with separate heating and
cooling thermostats.  For control function purposes, the 14 bays are sub-
divided into two distinct control zones of seven bays each.  One zone  is
further equipped with one additional heating and cooling thermostat per bay
and time clock switching to provide differential day and night temperature
control setpoints.

     A central control and status indication panel provides automatic  heating
or cooling operation mode selection and selection of outside or return air
for heating.  Selection of either outside or return air for heating is pro-
vided on a manual basis to afford humidity and temperature control in  each
zone of the greenhouse.  This selection is a manually controlled function
because of infiltration heat loss and heat exchanger coil  freezing problems
associated with automatic outside air intake dampers.

     The air heating thermostat in any bay initiates the starting of primary
pumps for water circulation through the heat exchange coils as well as
starting the fan(s) associated with that particular bay.  The starting of
centrifugal air handlers initiates the delayed opening of return or outside
air dampers to prevent rapid inflation damage to the polyethylene air dis-
tribution ducts.

     A primary starting circuit is incorporated into the control system to
provide determinant starting times.  That is, the first heating thermostat
in a zone starts one of the 3.73 KW (5 hp) primary circulation pumps.   The
second 3.73 kw (5 hp) pump in the particular zone is started, to operate in
parallel with the first pump, when a prescribed number of heating thermostats
"made" are activated.  When the heating requirements of the zone are satis-
fied, both pumps are stopped and the initial pump starting sequence 1s
reversed to average overall pump operation time.

     The soil heating thermostat in each zone is integrated with the seven
air heating thermostats to provide primary control.  In addition to primary
pump starting, the soil heating thermostats provide starting signals for
secondary (0.75 KW/zone (1 hp/zone)) soil heating system booster pumps.

     The cooling system control is automatically segregated from heating
control.  The cooling system is controlled by a thermostat in each bay
starting and stopping the appropriate exhaust fans.

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DATA COLLECTION SYSTEM

     The greenhouse is fully instrumented with an automatic data collection
system to provide a complete environmental history and to establish  energy
balances to assess the technical  feasibility of the warm water heating system.
A microprocessor-control led data  acquisition and recording system scans 227
data transducers at one-half hour intervals.  The data are recorded  on paper
tape and magnetic tape and are computer processed to provide time function
relationships of pertinent environmental  and water conditions.

     Temperatures are measured at 10 individual points in each of the 14 bays
of the greenhouse.  Three dry bulb temperatures are monitored at each of
three random locations in each bay.  The three temperatures measured at each
location include one soil temperature, at random depths from 10.2 cm (4 in)
to 30.5 cm (12 in) below grade, one air temperature below the plant  canopy
and one air temperature near the  top of the plant canopy.  Dew point is also
measured at one location in each  bay.

     The ambient conditions of air, dry bulb temperature and dew point, are
monitored at one location outside the greenhouse.  Total incident solar
radiation is monitored at one location inside the greenhouse and at one
location outside the greenhouse at rooftop elevation.

     The balance of the points monitored include greenhouse main supply and
return water temperatures, soil heating system supply and return water
temperatures, and supply and return air and water temperatures on four heat
exchangers.  Manual readings were also recorded daily of total greenhouse
water flow, soil heating water flow and electrical power consumption of
circulating water pumps, heating fans and ventilating fans.

     Air dry bulb and soil temperatures are measured with 24-gauge, copper-
constantan thermocouples, air dew point is measured with heated lithium
chloride electrical hygrometers and water temperatures are measured with
immersion type copper-constantan thermocouples.  Solar radiation is measured
by star pyranometers and is recorded as hourly integrated values.

HEATING SYSTEM PERFORMANCE AND OPERATING  EXPERIENCE

     Operation of the warm water heating  system began in December, 1975.
Since the Sherco Greenhouse was operational before the start  up of Sherco
Generating Unit  I, condenser waste heat temperatures were simulated by the
use of electric  boilers.   In the 1975-76  heating season, the  primary heating
objective was to verify the heating system  design.  Water flow  rates, air
flow rates, temperature drops, greenhouse heat demand, and other variables
were observed and recorded manually for comparison with  design  values.
Several simulation runs using 29.4°C  (85°F) water confirmed the design capa-
bility of the heating system to transfer  the  heat necessary to  maintain
greenhouse air temperatures in an  acceptable  range of  13-16°C (55-60°F) on
the coldest nights,  -29°C  (-20°F), experienced.
                                      11

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     In September,  1976, the Sherco Greenhouse was first supplied heat
directly from Sherco Generating Unit I.  The heating objective during the
winter of 1976-77 was to verify that the waste heat available from the oper-
ating power plant was adequate for heating the Sherco Greenhouse.  By utiliz-
ing an automatic data logger, 227 data points were monitored and recorded
at 1/2 hour intervals throughout the heating season, including all heat
transfer and greenhouse environmental parameters of interest.  This compre-
hensive data set proved beyond all doubt the technical feasibility of
utilizing actual power plant waste heat to provide a suitable greenhouse
environment for the production of floral and vegetable crops.

     In the third year of operation, the 1977-78 heating season, the main
technical objective was to solve some heat exchanger and pipeline fouling
problems identified in the previous heating season.  Of course, additional
heating system performance data were taken and analyzed to add to,the body of
experience previously gained.  Of particular interest in the 1977-78 heating
season was the observation of the variation of condenser outlet water temper-
atures with generator unit loading.  Prior to the 1977-78 heating season,
the Sherco Generating Plant had only one operating unit.  With the addition
of Unit II, the station began to operate as a load following rather than
baseload facility.

     In order to completely document the technical performance of the Sherco
Greenhouse Project, particularly the heating system performance, the balance
of this section of the report is divided into three parts, each dealing with
a specific aspect of the technical performance of the heat source, the heat
delivery, and heat transfer systems.

SEVERE COLD WEATHER PERFORMANCE DATA

     The greenhouse heat loss reached near design conditions when outside
ambient air temperatures fell to -29 to -34°C (-20 to -30°F).  Oftentimes
when this occurred, the waste heat warm water available from the power plant
was significantly warmer than the design temperature of 29.4°C (85°F).  For
example, Figure 6 shows the condenser outlet water temperature available to
the pipeline for delivery to the Sherco Greenhouse on January 9, 1977.  This
date was chosen because it was the coldest day ever recorded during the
project.  The corresponding generator unit output shown in Figure 6 is
typical of baseload operation of the Sherco Generating Plant.  As indicated
in Figure 6, a 24-hour average condenser outlet water temperature of 37.6°C
(99.6 F) was recorded.  At the same time, the average water temperature
measured at the greenhouse inlet was 36°C (96.2°F) shown in Figure 7.  The
average ambient air temperature on January 9, 1977 was -31°C (-23.8°F),
with a high of -23°C (-10°F) and a low of -42°C (-42.9°F) at 8:00 a.m.  The
heat transfer systems in the greenhouse were able to maintain an average
greenhouse air temperature of 15°C (59.5°F) with an 8:00 a.m. low of 14°C
(58°F) using warm water available at 33°C (91.1°F).

     The complete air and soil  heating system AT averaged 3°C (5.3°F) while
the inside to outside air AT averaged 46°C (83.3°F).   The 24-hour average
heat transfer rate based on the total  design water flow rate of 32.7 1/s
(518 gpm) was 402 KW (1.4 X 106 Btuh).

                                     12

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      750
      700
  »—

  D_
  Oi
  O

  
-------
LU
QL
      op     OQ


     120
no

100


 90


 80

 70


 60


 50


 40


 30


 20 J

 10


  0


-10 _

-20


-30

-40


-50
         -- 10
          -40
          -30
          --10
            -20
          --30
         	40
                    WARM WATER SUPPLY  (96.2)*
WARM WATER RETURN (903
                  GREENHOUSE AIR (59.5)
                                              AMBIENT AIR (-23.8)
                                          *Numbers In parentheses are
                                           daily averages in °F
          02    4    6    8   10  12   14   16   18   20  22   24

                             TIME,  hr

         Figure 7  Heating System  Performance January 9, 1977
                                 14

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     Wind and solar radiation data for January 9,  1977  are  presented in
Figures 8 and 9 to complete the 24-hour environmental history.   The  wind
velocity data were those recorded by the National  Weather Service at
St. Cloud, Minnesota about 20 miles northwest of the Sherco Greenhouse.
Solar data were measured inside and outside the greenhouse  with pyranometers
and the hourly integrated values were recorded.  From these data, it is
obvious that January 9, 1977 was not a completely typical cold  day with 40%
cloud cover from sunrise to sunset; but, the light winds were fairly typical.

     Additional severely cold weather performance data  are  plotted in Figures
10 and 11.  The dates selected represent the two coldest days on record in
the 1976-77 and 1977-78 heating seasons.  January 10, 1977  was  nearly as
cold as January 9, and the second coldest day recorded  during the project.
It differed only slightly from the previous day in that clear skies  prevailed
from sunrise to sunset.  Again, greenhouse air temperatures were held above
14°C (58°F) during darkness hours when ambients dipped  to -33°C (-28°F)
using waste heat available at 37°C (98.5°F), 24-hour average temperature.

     Figure 10 indicates the same data for January 9, 1978, which coincident-
ally was the coldest day of the 1977-78 heating season.  It may be noted  that
the waste heat was available at slightly higher temperatures, but the green-
house air temperature was actually lower.  No abnormal  environmental con-
ditions were noted to explain the apparent difference from  previous data.
It is possible that reduced temperature set points on the greenhouse
thermostats controlled the temperature to the lower than expected value.

     Figure 12 is the same data for February 2, 1978.  Here, satisfactory
space temperatures were maintained in the greenhouse when the waste heat
source water temperature was 32°C (90°F), near the design water temperature,
and ambient outside air was -20°C (-4°F).

     More insight into heating system performance can be gained by a detailed
look at the performance of the air heating and soil heating systems separately.
Figure 13 shows the finned-tube heat exchanger inlet and outlet water and air
temperatures for the 24 hours of January 9, 1977 as measured at the heat
exchanger located in the easternmost bay of the greenhouse.  The inlet air
temperature to the heat exchanger was essentially the average air temperature
in that particular bay of the greenhouse.  It  can be seen that the water was
being cooled approximately 4°C  (8°F) while air was being heated 9°C (16°F).
Both the waterside and airside  AT's were below design values.  The logarithmic
mean temperature difference of  the heat exchanger averaged 14°C  (25.3°F)
with an average heat transfer rate of 24.4 KW  (117,450 Btu/hr)  at the design
water flow rate.  This measured performance was 60% of the design value as
a  result of heat exchanger tubeside fouling.   However, due to the average
warm water temperature being 6°C  (11.2°F) above design,  the potential adverse
consequences on greenhouse air  temperature were avoided.

     Typical soil heating performance data are shown in  Figure  14 for January
9, 1977.  The  soil temperature  plotted  is the  average of 42 soil temperatures
measured  at depths varying from a  2.5-30 cm  (1-12 in) through the total
2123 m2  (22,848 ft2) growing space.  The water  AT in  the  soil heating system
was relatively constant at 3°C  (6°F).   Since water  flow  in the  system was

                                      15

-------
02    4    68    10  12   14   16  18    20  22   24
                   TIME, hr
   Figure  8  Wind Speed January 9, 1977
                       16

-------
Btu/hr-ft2

     TOO
KJ/hr-m2
                               EXPECTED /

                                   V/
                      8
                       10     11     12     13     14     15     16

                                   TIME, hr
17
              Figure 9  Measured Hourly Average Total  Solar  Radiation January 9,  1977
                       Sunrise to Sunset Sky Cover =  40%
                       Wind Speed =  5.75 miles/hr from East
18

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UJ
Q.

°F

120


no


100


  90


 80


  70


  60


  50


 40


 30


 20


 10


  0


-10


-20


-30


-40


-50
           L 40
           - 30
             10
           - 0
           - -10
           --20
                    WARM WATER  SUPPLY  (101.2)*
                    WARM WATER  RETURN  (92.3)
             20      GREENHOUSE AIR  (58.3)
                                                   AMBIENT AIR  (-10.4)
           --30
            -40    *Numbers  in  parentheses are daily averages in °F
          02    4    6    8   10    12  14   16   18  20   22   24

                              TIME, hr

                Figure 10  Heating System Performance  January 9,  1978
                                 18

-------
UJ
OL
°F

 120 _


 no _


 100 _


  90 _


  80 _


  70 _


  60 _


  50 _


  40 .

  30 .


  20 .


  10 .

   0 ,


 -10 _


 -20 .


 -30 ,


 -40 <


 -50
              WARM WATER  SUPPLY  (98.5) *
          - 30
          - 20
            10
          -  0
          - -10
          - -30
WARM WATER RETURN (92.8)
                        GREENHOUSE AIR (59.2)
                                                 AMBIENT AIR (-18.8)
            _40    *Numbers in parentheses are daily averages  in  °F

                                                 —I	1	1	1
         0    2    46    8   10   12   14  16    18   20   22  24
                              TIME,  hr

            Figure 11  Heating System Performance January 10, 1977
                                19

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CC.
 °F

120

no


100

 90


 80


 70


 60

 50


 40

 30


 20


 10


  0

-10


-20

-30


-40


-50
                WARM  WATER  SUPPLY  (97.1)*
           -30
                WARM WATER RETURN(91.2)
             20
             GREENHOUSE AIR  (63.
          -- 10
           - 0
           --10
              AMBIENT AIR (-1.
             -20
           "-30
            -40   *Numbers in parentheses  are daily averages in °F
          0    24    6    8   10  12    14    16   18  20   22   24
                             TIME, hr

           Figure 12  Heating System Performance February 2,  1978
                                 20

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°F
110
100
 90
 80
 70
 60
  50
  40
     - 40
     - 30
SUPPLY WATER (96.2)*
         RETURN WATER (88.1)
         OUTLET AIR (74.5)
         INLET AIR (58.9)
       10
            *Numbers  in  parentheses  are daily averages in °F
      02    4    6   8   10   12   14   16  18   20   22  24
                          TIME, hr
       Figure  13  Air heating System Performance January 9,  1977
                            21

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Q-

&
      °F
      no
      100
       90
           - 40
       80 _
       70
       60
       50
       40
                   SUPPLY TEMPERATURE  (96.2)
RETURN TEMPERATURE  ( 89.0)
           - 20
                   SOIL TEMPERATURE  (61-
          -- 10
                  *Numbers  in  parentheses are daily averages in °F
          0    2    46    8   10   12   14  16   18   20   22  24

                              TIME, hr

            Figure  14  Soil Heating System Performance January 9,  1977
                      Sunrise to Sunset Sky Cover = 40%
                                  22

-------
also constant, the design flow rate of 7 1/s  (112  gpm)  gave  a  nearly  constant
heat transfer rate of 98.4 KW (336,000 Btu/hr)  or  46 watts/m2  (14.7 Btu/hr-
ft2).  However, the measured water flow in the  soil  heating  system was
normally about 5 1/s (80 gpm); thus, a heat transfer rate of 70.3 KW
(240,000 Btu/hr) or 33 watts/m2 (10.5 Btu/hr-ft2)  was actually achieved.
This contrasts with the air heating system design  heat transfer rate  of
295 watts/m2 (92 X 106 Btu/hr-ft2) of greenhouse floor area.  The rise  in
soil temperature after 10:00 a.m.  in Figure 14  is  apparently due to higher
water temperatures in the heating  grid, higher  air temperatures in the
greenhouse, and higher solar radiation heat flux.   Thus, soil  heating
amounted to a little more than 10% of the total heat transferred, but some
of this heat was lost to the earth and did not  contribute to heating  the
greenhouse air.

     Besides the coldest day data, the monthly  overall  performance during
January, 1977 and January, 1978 has been analyzed.  Figures  15 and 16
present the distribution of warm water and average greenhouse air tempera-
tures for the month of January, 1977.  Because  Sherco Generating Unit I was
operating more or less base loaded, 29.4°C (85°F)  water was  available 99.6%
of the time.  With this warm source water, it was  straightforward (in spite
of heat exchanger fouling) to maintain greenhouse  air temperatures above
13°C (55°F) 99.9% of the time.

     Figure 17 shows the waste heat temperature distribution available  for
greenhouse heating January, 1978.   These data were taken from plant operating
logs and are a composite of the operating data  for the two-unit station.
In January, 1978 an interconnected pipeline system was in operation so that
waste heat could be made available from either generating unit in the event
of unit outages.  By careful manual selection of the waste heat source, it
was  possible to provide waste heat at a temperature above 29.4°C (85°F),
73%  of the time, even though Unit I and Unit II produced warm water greater
than 29.4°C (85°F) only 50% and 65% of the time, respectively.  With the
available waste heat, air temperatures in the Sherco Greenhouse were main-
tained above 13°C (55°F) 86% of the time  (Figure 18).  The difference
between January, 1977 and January, 1978 resulted from the change in plant
operation from a single-unit baseload station to a two-unit load following
station.  When operating in an electric system load following mode, the
gross electrical output of each unit can  vary from 700 MW in the daytime
down to a minimum load of about 300 MW  in the nighttime.  This electrical
load variation can result in an 8°C  (15°F) change in condenser outlet water
temperature as  illustrated in  Figure 19.

ELECTRIC ENERGY CONSUMPTION

     Of particular concern in  the design  of mechanical  systems to utilize
waste heat  is  the operating electrical  energy  requirement.  In order to
assess  the  overall  feasibility of waste heat utilization for greenhouse
heating, careful  records of electrical  energy  consumption were maintained.
Manually read  electric meters  were  installed to measure separately the
electric energy consumption of the  Sherco Greenhouse air heating  system fan
motors, water  circulation  system  pump motors,  cooling  system  fan  motors,  and


                                      23

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                 100
                  80--
ro
           c
            3
           IO 
           -M id
           (U
           Q.
60..
                 40--
20 „_
                             20
                                     Greater Than 85°F
                                     99.6% of the Time
                                     in January, 1977
                                    30
                              40
                    60
               70
80
90
100
  I
no
120
                                         Figure 15  Typical Warm Water Temperatures

-------
ro
01
                100-
          to
          -C
          0) 0)
          +•> S-
          (O 3
          
          S- (O
          t!3 J-
            O)
          •r- 0)
i*- -o
O 0)

0) 3
          0>
          o
          5-
          0)
          0.
                 80-
      60-
40-
                20-
                                10

                               4-
                              Greater than
                              55°F 99.9% of
                              the Time in
                              January 1977
                                             20
                                              I
                   40
                      50
                            60
70
80
90
100   °F
                                          Figure  16  Typical Greenhouse  Air Temperature

-------
ro
          OC
          UJ
          O.
              25
              20
              10
                  40
                                                                       732 of
                                                                        Time
                                                                    Temperature
                                                                    Greater than
                                                                        85°F
T
50
 i
60
 i
70
 i
80
 I
90
100
110
120
130
                                                       TEMPERATURE, °F
                          Figure  17   Condenser Outlet Water Temperature Distribution January, 1978
                                     Composite of Unit  I and Unit II

-------
ro
                                                    of
                                                Time
                                                Temperature
                                                Greater Than
                                                55°F
                     30       40        50       60        70       80        90       100      110
                                                   TEMPERATURE,  °F

                          Figure 18  Average Greenhouse Air Temperature Distribution January 1978

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             120  -
                  I-   50
rv>
00
        ae.

        1
        UJ
        Q_
        UJ
110


100


 90


 80


 70


 60
                   -  40
_  30
                  "-  20
              50  --  10
                       100
                        I
                      200
                            300
 i
400
 i
500
600
700
                                                   GENERATOR UNIT LOAD, MW
                                Figure 19  Typical Warm Water Temperature Variation  with  Unit  Load

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miscellaneous electrical  usage.   Back up heating energy supplied by electrical
boilers was determined by subtracting all the separate readings from the
Sherco Greenhouse master service meter.

     Figure 20 shows the monthly total power consumed by the heating fans
and circulating water pumps in the greenhouse during the 1976-77 heating
season.  Beginning in October the curve shape is characteristic of the heat-
ing degree days associated with each month of operation.  It should be
noted that the weather turned abnormally cold in November with 1249 heating
degree days compared to a normal of 1050.  In contrast, February was abnorm-
ally warm with 1283 heating degree days as opposed to a normal of 1448.  One
may notice that the peak electric energy use of the pump motors is nearly
80% of that of the fan motors even though the installed pumping capacity is
one half that of the fans.  This is due mainly to two factors:  the method
of flow control (parallel pumping) and over capacity in the pumping system.
The sharp decline in pumping energy consumed in February resulted from
using half of the installed pump capacity, in addition to the change in
the weather conditions.  The sharp rise in March was due to continuous
operation of one half of the pump capacity to facilitate heat transfer
measurements.

     Using the previous data, Figure 21 was generated to show what percent of
the installed heating system capacity was used on a monthly average basis.
These data proved useful in estimating the electric energy use that commercia1
operations might expect.  Again, it may be noted that the water pumping
capacity factors are high, compared to the fans because only  four pumps can
start or stop; whereas, the air heating system can start or stop 14 fans.

     Table 1 summarizes the annual electrical use of all the  greenhouse
systems.  For 1976-77, the period covered is October 1, thru  May 31, while
in 1977-78 a complete year starting and ending on June  1 is presented.  The
amount of electrical energy consumed by the warm water  heating system  fans
and pumps was greater in 1977-78 due to the longer period covered and  due to
the differences in warm water temperatures available from the power plant.
The total energy consumed by the fans and pumps in 1977-78 is estimated to be
8.5% of the  total energy required to heat the greenhouse during the year.
Thus, the warm water heating system had  an annual ratio of heat delivered to
electric energy consumed of  11.8, which would be equivalent to a heat  pump
COP of the same value.  The  instantaneous ideal rated heat output to electric
energy input of the Sherco Greenhouse heating system is 12.7.

     The energy consumed by  the  backup  heating  boilers  was necessitated by
pipeline outages, reduced condenser outlet water temperatures, and  generator
unit outages.

     A total of 642  hours of operation  without  waste  heat  available were
recorded from  October  1,  1976  to April  25,  1977, at which  time  the  pipeline
was shut down  for maintenance.   Therefore, with an overall  availability  of
warm water waste heat  of 75% for the  period  October  through May,  backup
electrical energy  during the first  heating  season  amounted to 249,661  kwh or
about  16%  of the total  calculated  annual  energy required.   Figure 22  shows


                                     29

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      15
      10
o
Q.

O
i—<
OL

O
       0
                                          FANS
                OCT    NOV
DEC    JAN

   MONTH
FEB    MAR    APR
MAY
      Figure 20  Monthly Electric Power Consumption of

                 Heating Fans and Pumps (1976 - 1977)
                                  30

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oc

P
o
o

>-
       80
       70
       60
       50
       40
       30
       20
       10
                                            CIRCULATING PUMPS
OCT    NOV
                                DEC   JAN


                                  MONTH
FEB    MAR    APR    MAY
        Figure 21   Monthly Capacity Factors of Greenhouse

                   Heating System Units  (1976 - 1977)
                                   31

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          TABLE  1.   SHERCO  GREENHOUSE  ELECTRICAL  POWER  CONSUMPTION


                                10/1/76  -  5/31/77  6/1/77 - 6/1/78
      Use                              KWH               KWH

      Warm Water Pumps               48,647             52,846
      Heating  Fans                   63,766             79,188
      Cooling  Fans                     4,506             10,813
      Miscellaneous  Use              37,220             56,160
      Boilers  &  Well  Water  Pump      249,661             555.793

                         Total       403,800             754,800


the characteristic monthly energy use  by the Sherco Greenhouse  boilers during
times of generator unit outages during the 1976-77 heating season.   It should
be noted that 32,500 kwh of the supplemental heat was used during May when
the pipeline was taken out of service.  Thus, the adjusted supplemental heat
discounting May was 217,161 kwh, or 13.9% of the calculated annual  heat energy
requirement.

      The  second heating season was similar to the first except that almost
twice as much backup heat was required.  This was due to several factors,
the most  important being fouled heat exchangers, lower average condenser
outlet water temperatures, pipeline failures, and pipeline unavailability in
August, September, and October, 1977 necessitated by commercial expansion of
the waste heat pipeline system.  Based on degree day data, an estimated
151,025 kwh were used for heating during  these three months.  Hence, the
adjusted supplemental heat consumed was 404,768  kwh or about 32% of the
annual greenhouse heat requirement.  Since this  percentage of supplemental
heat  addition would likely be considered unacceptable by commercial waste
heat  users, it should be noted that a commercial greenhouse operator, who
used  the same waste heat source with unfouled (clean) heat exchangers during
the same heating season, required only a  10% supplemental heat addition.

WASTE HEAT AVAILABILITY

      The pipeline installed to transmit the condenser waste heat 1067 m
(3500 ft) each way to the Sherco Greenhouse and  back to the Unit I cooling
tower basin went into service on September 16, 1976.  The main 30.5 cm
(12 in) diameter pipeline operated flawlessly until April 25, 1977 when it
was taken out of service for cleaning and inspection.  However, a 15 cm
(6 in) diameter service pipeline that brings warm water into the greenhouse
from  the main pipeline failed three times during the 1976-77 heating season.
These failures resulted in the loss of waste heat service to the greenhouse
for 75.0, 21.5, and 29.0 hours during the months of December, February, and
March, respectively.  Warm water service  availability to the greenhouse
due to these failures was reduced to 96.6%.  However, the overall avail-
ability of waste heat at the greenhouse was only 87.9% due to the combined
effects of both pipeline failures and generator  unit outages.  Table 2

                                     32

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summarizes the Unit outages and pipeline failures month-by-month for the 1976-
77 heating season.

     During 1977-78 heating season warm condenser water was supplied to the
Sherco Greenhouse and to commercial greenhouse operators.  In order to do
this, the pipeline network was expanded and an interconnection to Unit II
was made.  Thus, waste heat could be made available from either generating
unit by manual operation of valves at the point of interconnection of the
two units.  Normally these valves were operated when operating personnel were
notified of a generator unit outage.  With this feature it was possible to
have a constant supply of waste heat available to the pipeline except for
the time it took to switch the valves during unscheduled generator unit
outages, and  except for a single simultaneous two-unit outage which occurred
in May.  For a period of 56 hours, Unit I was out of service for annual
maintenance and Unit II was intentionally scheduled out for weekend mainten-
ance.
                      TABLE 2.  WARM WATER AVAILABILITY
        Month

        September 16,  1976
        October
        November
        December
        January
        February
        March
        April 25, 1977

          Total or Average

Sherco
Unit I
Outages
(hrs)
32.0
229.5
0
7.5
168.0
78.5
0
0
515.5


Pipeline
Failures
(hrs)
0
0
0
75.0
0
21.5
29.0
0
125.5
Overal 1
Availability
of Waste Heat
@ Greenhouse
(percent)
90.5
69.2
100.0
88.9
77.4
85.1
96.1
100.0
87.9
      Table 3 summarizes the weekly overall  availability of waste heat at a
 commercial operator's greenhouse for the period November 2, 1977 to May 31,
 1978.  Prior to November 2, 1977 the pipeline system was out of service for
 construction to extend service to commercial  operators.  While the pipeline
 continued in service after May 31, 1978, the greenhouse heating season was
 essentially over.  As indicated, for a period of 4848 operating hours an
 overall availability of 96.4% was achieved.

      On a weekly basis during the first heating season, there were only four
 weeks out of 30 when warm water was unavailable for part of the time.  Un-
 available service to the commercial greenhouse operations was primarily due
 to pipeline failures.  Two pipeline failures occurred during the heating
 seasons:  one was the failure of a service line from the main pipeline into
 a commercial floral operation and the other failure involved a main 30.5 cm
                                      33

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           TABLE 3.   SUMMARY OF WARM WATER AVAILABILITY
                               AND TEMPERATURE
                                                       85°F or
                          Service Availability         Greater
     Dates                   (Hrs)       (%)               (%)

 11/2  -  11/8                156         100               95
 11/9  -  11/15                168         100               93
 11/16  -  11/22                168         100               92
 11/23  -  11/29                168         100               57
 11/30  -  12/6                168         100               69
 12/7  -  12/13                 80          47.6             84
 12/14  -  12/20                158          94.0             84
 12/21  -  12/27                168         100               74
 12/28  -  1/4                  168         100               40
 1/5    -  1/11                168         100               96
 1/12  -  1/18                168         100               98
 1/19  -  1/25                168         100               97
 1/26  -  2/1                  142          84.5             95
 2/2    -  2/8                  168         100               81
 2/9    -  2/15                168         100               98
 2/16  -  2/22                168         100               47
 2/23  -  3/1                  168         100               99
 3/2    -  3/8                  168         100               87
 3/9    -  3/15                 168         100               82
 3/16   -  3/23                 168         100               90
 3/24   -  3/29                 168         100               92
 3/30   -  4/5                  168         100               86
4/6    -  4/12                 168         100               87
4/13   -  4/19                 168         100               92
4/20   - 4/26                 168         100               85
4/27   -  5/3                  168         100               88
5/4    -  5/10                 112         66.7             91
5/11   -  5/17                 168         100               92
5/18   - 5/24                 168         100               94
5/25   - 5/31                 168         100               97

  Totals  or Averages       4848         96.4
                                34

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OL
LU
                 OCT    NOV    DEC    JAN    FEB    MAR    APR    MAY

                                  MONTH

       Figure 22  Monthly Electric Power Consumption of Greenhouse
                  Boilers During Unit I Outages (1976 - 1977)
                                    35

-------
 (12 in) diameter plastic pipeline.  In the former case, a four-day outage
 occurred; in the latter case, a 26-hour outage occurred.  The period of un-
 available service indicated in May was during the previously mentioned two-
 unit outage of the generating station.

      It is also noteworthy that warm water at the power plant condenser out-
 let was available at a temperature greater than 29.4°C (85°F) for 85.4% of
 the time.  However, the actual  temperature delivered to the  Sherco Greenhouse
 was somewhat lower due to pipeline heat losses.  Figures 23  and  24 illustrate
 typical piping heat losses from the condenser outlet to greenhouse inlet for
 warm water taken from Units I and II,  respectively.   The temperature drop is
 greater during daylight hours when pipeline flows are low.   During periods
 of higher flows, the AT averages about 1.2°C (2.2°F) when the Unit I source
 supply is used and 3.1°C (5.6°F) when  the Unit II source supply  is used
 The difference in pipeline heat loss for the two sources results  from the
 differences in pipe diameter, pipe material, and total  transmission  distance
 Based on a nominal  pipeline flow rate  of about 63.1  1/s (1000 gpm),  the
 pipeline heat loss  from the Unit I source was about  300 watts/m  (312 Btu/hr-
 ft).   This loss rate is about twice that calculated  for the  desiqn basis
 with 29.4°C (85°F)  water temperature.                            y

 OPERATING EXPERIENCE

      Construction work on the Sherco Greenhouse began  in August  of 1975   The
 greenhouse and the  mechanical equipment were installed  to provide  a  commer-
 cially oriented demonstration project,  which employed  systems  and  practices
 currently accepted  by  the commercial greenhouse industry.

      The   exception to this,  of course,  was  the installation  of  the  warm
 water air and  soil  heating  systems.  The greenhouse  system was constructed
 by  union  craft  labor under  the  supervision  of project  personnel.

      The  heating  system was made operational  by November, 1975.  During the
 heating season  of 1975-76,  the  greenhouse heating proved  to be satisfactory
 under a simulation  scheme.  That is, warm waterwas provided by two - 390  KW
 (1.28 X 106 Btu/hr)  electric  boilers at  a temperature simulating the antici-
 pated winter design  minimum condenser outlet  cooling water temperature of
 29.4°C  (85°F).  The  first year  of operation  involved the  technical verifi-
 cation of  the heating  system  performance as  designed.   Preliminary tests
 indicated  that  the  heating system design was  adequate in  all  conditions
 experienced, and any problems associated with  the initial operation of the
 various system  components were  diagnosed and  remedied.

     On the basis of the successful first year  of operation,  the connecting
pipeline was installed  during the  summer of  1976 to utilize condenser reject
heat from Unit  I, which began commercial operation in the spring of 1976
The greenhouse  circulation water  pipeline source is at a cooling tower supnlv
riser pipe as shown  in  Figure 25, with circulation flow through the pipeline
being provided  by the  available head pressure at the tap point as developed
by the Sherco main circulation  pumps.
                                     36

-------
Ul
0£



1
       90
                             CONDENSER OUTLET WATER
                                SIX-INCH SUPPLY  WATER
           0    24    6    8   10   12   14   16  18   20   22  24


                               TIME, hr
            Figure  23   Pipeline Losses Between Unit I Condenser
                       and Greenhouse January 8, 1978
                                  37

-------
CL.
     °F


      110
      105
           -  40
      100
       95
       90 _
        85
       80
          -_   35
                            CONDENSER OUTLET WATER
                              SIX INCH SUPPLY WATER
          0    2    46    8    10   12   14  16   18   20   22   24


                              TIME, hr
           Figure  24   Pipeline Losses Between Unit II Condenser
                      and Greenhouse January 10, 1978
                                 38

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                   Figure 25  Connection at Cooling Tower


     The connecting 1067 m (3500 ft)  greenhouse supply and return pipelines
consist of 30.5 cm (12 in) diameter low pressure polyvinylchloride pipe.
The pipeline is uninsulated and is buried at a nominal depth of 1.52 m (5 ft).
The above ground piping at the cooling tower is insulated and heat traced to
minimize heat loss and freezing problems during periods when no flow exists
in the pipeline.  The initial water flow capability of this pipeline was
100 1/s (1600 gal/min) after completion of installation in September, 1976.

     In the Summer of 1977, an interconnection between the two generating
units was made to provide commercial  waste heat service with two-unit
reliability.  The Unit II supply connection is at a cooling tower riser,
similar to the Unit I connection, and a pipeline interconnects to the pre-
viously existing pipeline from the Unit I tower.

     Figure 26 shows in schematic form the Sherco warm water distribution and
service pipeline system as it existed during the 1977-78 heating season.  As
indicated, the installed  Unit II connecting pipeline  is a 45.7 cm (18 in)
diameter cast  iron pipe which is uninsulated and buried to a nominal depth
of 1.52 m  (5 ft).  This portion of the pipeline was intentionally oversized
to be capable  of delivering  sufficient flow to heat up to 5.7 hectares (14
acres) of  greenhouses at  the  present  development portion of the  Sherco site.

     Also  indicated in  Figure 26  is the method of  providing warm water service
to the commercial  customer.   The  service  connections  are  installed  as a
typical utility service,  where  flow from  the main  pipeline  enters the service
supply pipe, passes through  a  recording flow meter and then  is distributed  by
the  user's pumps  to the greenhouse heating  system  prior  to  being returned to
the  main  return pipeline.
                                      39

-------
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                OLE
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                                                                            TERMINATION -
                                    i^j

                                   31
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                                                                                                                 "t-^l  *  I    MA.IN

                                                                                                                  /     I f iRC.ULA.TlNC.
                                                                                                                 _•      *   f~, D *:f
                                                                                                                  | L _  I  ______
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                                                                                                                  I T<-J T'-,^tQ Dl*rR.«uT.

                                                                                                     CHLOKIN/XTION

-------
                                      *c^o

                                      .veto
                                                                                        FITTING AND
                                                     MM watt oimtmnitm MO SPNICI HNIM JTSTW >M.«I
                                                                4*  Httt
                                                                If XtM
                                                                1/4' <-*tt - *M*t ATM* • Mtt I I,
                                                                                      ,2, ^
                              (
                              A
                              ^rr-.,
                                                        * «**•«*• ta**V *  '•*• » "•»« "•« h
                                                        • J«**1*t 4H*i« 4*  'it* • Mutt *•» »
                                                  I-U   (C* »
                                                  0-tt   JCG 1
                                                  ••II   * *
                                                  M4   rt* l|
                               fsj
                                   Q'-'™
                                                                                       -4- f-C
C.IS7
; t F T •
Figure  26  Warm Water  Distribution  System Schematic

-------
OPERATING PROBLEMS

Coil Fouling

     In November of 1976, after about two months of heating with condenser
cooling water, the overall heat transfer capability of the finned-tube coils
in the Sherco Greenhouse appeared to be reduced by about 40% from design
conditions.  Further investigation indicated that waterside coil tube fouling
was the reason for loss of performance.  Chemical analyses of samples of
material deposits from various system components indicated that the fouling
was caused by a microbial-based slime.  Remedial action in the form of
chemical or mechanical cleaning was recommended.

     Mechanical cleaning of the coils was investigated, but found to be an
unworkable solution.  This was due to the difficulty in accessing the tubes
in the particular coils used in the Sherco fan/coil units and also to the
presence of spiral-wound turbulence-inducing wires on the inside surface on
the coil tubes.

     Various chemical  cleaning programs were also investigated and attempted.
Routine chlorination was determined to be the most effective means of slime
accumulation control.   The removal of the heat exchanger deposits was further
complicated by the formation of iron oxide deposits on the interior walls of
the carbon steel distribution piping in the greenhouse.  It was determined
during the 1977-78 heating season that acid cleaning of the greenhouse
internal circulation system was the most viable option, and this procedure
was adopted as routine maintenance is required.

     Based on the experience of the Sherco Greenhouse during 1976-77, general
recommendations on system component materials were offered to the commercial
customers who installed systems during the summer of 1977.  The recommenda-
tions were that the finned-tube coils be fully accessible for mechanical
cleaning and that distribution piping be of a non-oxidizing, easily cleaned
material.

Pipeline Fouling

     Concurrently with the fouling of the heat exchangers, a marked decrease
in flow capability of the main pipeline was exhibited.  The original 100 1/s
(1600 gal/min) capability was reduced by about 40% to 60 1/s (1000 gal/min)
over the first two months of pipeline operation.

     The cause of this flow reduction was indicated again as microbial based
slime accumulation on the interior of the pipe walls.  It was found that the
generating plant's routine chlorination to prevent condenser tube fouling
was not effective in preventing fouling of the greenhouse system, because of
the location in the circulation system where the condenser water is diverted
for the greenhouse system.

     The successful solution to the removal of pipeline slime deposits in-
volved mechanical cleaning using polyurethane "pigs" which were propelled


                                     42

-------
through the pipe by water pressure.   After this  mechanical  cleaning  operation,
the original full flow capability was restored.

     The experience in pipeline and  waterside coil  fouling  impacted  the
design of the commercial  service pipeline as installed in 1977.   The pipeline
source connections have fittings for mechanical  cleaning access.   Remote
chlorine injection systems were also installed at both the  Unit  I and II
source connections to allow for routine supplemental  chlorination to prevent
slime formation.  Inspection of the  commercial grower's heat exchangers and
piping system has indicated that the routine chlorination program is effect-
ive in preventing slime deposition.

Circulating Water Pump Wear

     During the heating season of 1977-78, two instances of seal failure on
two of the  four Sherco Greenhouse circulation pumps were encountered.  Upon
inspection  of the seals, it was indicated by the equipment vendor that while
the pumps had been in service for three heating seasons, the exhibited
deterioration was unusual.  It was further suggested that the mechanical seal
wear was due to the abrasive action of a particulate material suspended in
the circulation water.   Inspection of the pump  impeller and housing  indicated
no apparent signs of abrasion or wear.

GREENHOUSE  SYSTEM OPERATION

     The general operation of the greenhouse  environmental  control  system  is
quite  straightforward.   With the mechanical equipment  automatically con-
trolled, the system as designed  requires minimal observation and attention
on the  part of  the greenhouse operator.  As is  substantiated by  the two
commercial  growers at  the Sherco  site, the mechanical  maintenance routine
is equal to or  less demanding than  that  of  a  conventionally heated  greenhouse
system.
                                      43

-------
                     GENERAL HORTICULTURAL CONSIDERATIONS


SOIL

     The greenhouse was constructed on a soil similar to Hubbard loamy coarse
sand.  This soil exhibits low water holding capacity, low cation exchange
capacity and low pH.  It was disturbed and reshaped during construction.
It was necessary to add pulverized dolomitic limestone, phosphate potash,
and nitrogen to a 0-15 cm (0-6 in) depth prior to crop installation.  Coarse
textured sphagnum moss peat was added to the rose beds at a 1:20 peat-soil
ratio to improve the water holding capacity.  This had the effect of lowering
the pH to 5.0-5.5 and subsequent additions of dolomitic and hydrated lime on
the soil surface have not been successful to date in raising the pH to a
6.0-6.5 optirflum.

     The geraniums were potted in a 3:2:2 and the cinerarias in a 1:1:1 soil-
peat-perlite mix containing 5.3 kg/m3 (5.36 oz/ft3) of treble superphosphate
(0-46-0).

IRRIGATION

     The irrigation water was obtained from a ground source.  No cooling tower
water was used for irrigation.  The water quality generally was as follows:
pH 7.7, total hardness 213 ppm (as CaCOa), Ca 55 ppm, and Mg 13 ppm.  Any
potential phytotoxic ions were at insignificant levels.

     Irrigation water was applied to the roses using a Gates perimeter system
fitted with 180° flat spray nozzles.  It was possible to water about 93.6 m2
(1000 ft2) simultaneously.  A soil tensiometer was employed to assist in
estimating soil moisture.  Water was turned on at a 10 centibars tension and
applied at 12.2 1/m2 (0.3 gal/ft2) at each watering.  Irrigation frequency
was subject to seasonal adjustment.

     The cut flower and vegetable crops were irrigated with Viaflow trickle
irrigation tubing.  The tubing was arranged so that each row of plants was
adjacent to a water source.

     The potted geraniums were grown on the surface of the heated soil.  Sub-
irrigation was supplied by capillary mat underlaid with a sheet of poly-
ethylene film.  Each mat was 1.22 m (4 ft) wide and wetted by means of three
lines of trickle irrigation tubing.

     The containerized nursery stock was irrigated with 360° spray nozzles
mounted on metal rods and elevated about 0.3 m (1 ft) above the container
surface.

                                     44

-------
FERTILIZATION

     Soil fertility levels were determined for soluble salts,  pH,  nitrate-
nitrogen, potassium, phosphorus, calcium,  and ammonium-nitrogen on a routine
basis at the University of Minnesota Soil  Testing Laboratory.   Periodic
foliar analysis was performed on the roses and on other crops  when visual
deficiency or toxicity symptoms developed.  Fertilizing during crop growth
was accomplished by injecting soluble fertilizer into the irrigation lines
with a single head injector set at a 1:100 dilution ratio.

     The rates of macro and secondary elements were added according to the
results of periodic soil tests.  Soluble microelement mix was  added once to
each crop with a low nutrient requirement and twice to crops with high
demand.  Specific microelements were applied when visual deficiency symptoms
were evident.  Potted geraniums had a 8 gm (4.6 oz) per pot of Osmocote
14-14-14 mixed into the potting soil after steaming.

     Carbon dioxide enrichment was supplied from three propane-fired gener-
ators.  A timer automatically actuated these units two hours prior to sunrise.
The C02 level at sunrise was 1500-2000 ppm and was allowed to gradually
decrease to ambient during the day.

PEST CONTROL

     Steam was not  available so, during the July  crop  changeover,  Vapam was
used for soil fumigation.  The soil was presaturated  with water and  the
Vapam  applied at 1  1/10 m2 (1 qt/100 ft2) with a hose and suction device.
The soil was water  saturated again after  Vapam application.   The  area was
allowed  to dry for  4-5 days, rototilled,  and  then  spot planted with  tomato
plants.  If  no phytotoxicity was  observed, crop  planting  into ground beds
was resumed.  This  treatment held weed growth to a minimum and appeared to
have reduced damping  off  in the snapdragon transplants.

     Two attempts were made at  introducing Encarsia  formosa into  the tomato
crop for biological control of whitefly,  Trialeurodes yaporariorum (Westwood).
Both attempts  proved  unsuccessful as the  Encarsia  population  could not expand
as  rapidly  as  the whitefly population.  Endosulfan 50 WP was  used for control
after  the Encarsia  failed.

     The two-spotted  spider mite, Tetranychus urticae (Koch),  infestations
occurred mostly  on  the roses  and  was controlled  with  Pentac 50 WP.

     Aphids, Macrosiphum spp,on flowering crops  were  controlled with Aldicarb
and on food crops  with MaTathion  25 WP.

      Because of the high air flow from  the heating system,  botrytis, Botrytis
cinerea, did not present much of a  problem for most crops.  Botrytis infected
the leaves  and stems  of mature tomato  plants after cooling  pad usage was
 started.

      The rose varieties Sonia and Belinda appeared most susceptible to
 powdery mildew,  Sphaerotheca spp.  Applications  of Pipron LC  and Parnon LC

                                     45

-------
were used for control.

     Rhizoctonia presented the greatest problem in lettuce and geranium.
Benlate was used on geranium and nothing was used on lettuce.  Few damping
off problems were encountered with snapdragons.

HARVESTING AND MARKETING

     The Spring 1976 tomato crop was picked at the light pink stage (10-20%
ripeness) and bulked into 13.6 kg (30 Ib) boxes.   These were transported  to
a Minneapolis retail store where they were graded and packed.  Some were
retailed at the store and the balance were marketed to other retail stores.
Bulk packing and transporting at this stage of ripeness caused excessive
bruising and cracking.   Better market quality could be obtained if the fruit
were allowed to mature  on the vine to between 60  and 80% ripeness.

     The Spring 1977 tomato crop was graded at the site into U.S.  No.  1,  2,
and unclassified according to U.S. Standards for  Grades of Greenhouse
Tomatoes.  Grade No. 1  was sized into nested plastic separators with 3 X  5,
4X5,5X5,6X5 and 6X6 count.  Two layers  of separators were placed
into a 9.1 kg (20 Ib) carton.  The holding quality of the product under these
conditions was much improved.  The packed tomatoes were not stored in  a
cooler but delivered on the same day to another local tomato grower who sold
the product through his established market channels.

     The Fall-Winter 1976 leaf lettuce was cut, washed and packed into 2.26
kg (5 Ib) boxes.  Bibb lettuce was packed 24 per box.  An excessive amount
of labor was required to wash out sand deposited in the plants from the soil.
Growing through a plastic film mulch would have done much to prevent this.
The finished product was delivered both to a wholesale produce house and  also
directly to a supermarket.

     Blooming geraniums and cinerarias were placed into flats and delivered
directly to retail outlets.

     The snapdragons were bunched into tens by color and cut to about 1 m
(39 in) in length.  A plastic sleeve was pulled over the floral spike and
the bunches placed in buckets containing preservative.  The bunches were
transported and sold directly to the wholesale market.

     Cut roses were bunched in bulk, placed into buckets containing preser-
vative, and taken to a local grower who performed the grading and marketing.
Monthly grading reports showing the quantity and average price for each
grading category were kept for the five cultivars.

     The selling price for all the produce varied according to the seasonal
supply and demand.  None of the crops were grown  for a contract price.
Demand was good most of the time and quality was  generally good.

DETAILED CULTURAL METHODS

     Table 4 lists the major crops grown and the cropping schedule.

                                     46

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     1976

     1976
     1976
     1976
     1977

     1977
     1977
     1977

     1977

     1977
     1978
     1978

     1978

     1978
     1978
    TABLE 4.

MONTH

January


June

July
August
December
January

February
May
July

October

November
January
February

May

June
July
CROPPING CHRONOLOGY

       CROP

  Tomatoes started
  Green peppers started
  Roses planted
  Tomatoes terminated
  Green peppers terminated
  Snapdragons started
  Lettuce started
  Geraniums started
  Snapdragons terminated
  Tomatoes started
  Lettuce terminated
  Geraniums terminated
  Tomatoes terminated
  Snapdragon transplants started
  Freesia started
  Tree  seedlings started
  Cinerarias transplants started
  Geraniums started
  Cinerarias terminated
  Freesias terminated
  Geraniums terminated
  Tree  seedlings terminated
  Snapdragons  terminated
  End of  project
TOMATOES

     Several cultivars of tomato were pi anted in the two spring crops to
determine their yield potential.  Table 5 shows the yield of marketable
No. 1 and 2 tomatoes.
         TABLE 5.  YIELD OF MARKETABLE NO. 1 AND 2 TOMATOES

     Cultivar	kg (Ib) per plant
                               SPRING 1976
     Ohio MR-13
     Ohio-Indiana Hybrid 0
     Super M
     Tropic
     Eurocross
     Tuckcross 520
                             2.8
                             3.2
                             3.2
                             3.4
                             4.0
                             4.3
                                                             (Continued)
                                     47

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                      TABLE 5 (continued)

Cultivar                                   kg (Ib)  per plant
                                                     (9.2)
                                                     (9.6
                                SPRING 1977

     Vendor                                     4.2
     Terrific                                   4.3
     Vendor 76                                  4.5       (9.9)
     Bruinsma                                   5.6      (12.3)
     Eurocross BB                               5.6      (12.4)
     Michiana                                   5.8      (12.8)
     Tropic                                     6.0      (13.2)
     Better Boy                                 6.5      (14.4)
     Tuckcross 520                              6.7      (14.8)


     Two factors could account for the difference in yield:  plant density
and soil fertility.

     The area per plant for the Spring 1976 crop was 0.24 m2 (2.60 ft2),
whereas for the Spring 1977 crop it was 0.37 m2 (4 ft2).  In addition, the
general soil fertility of the 1976 crop was too low and the 1977 crop was
more optimal.

     It should be noted that the differences between the cultivars are only
an indication since a totally randomized plot and statistical analysis was
not performed.

     The Spring 1977 crop was planted primarily to Tropic because the vege-
tative growth rate of the vine was less vigorous than other red-fruited
cultivars and red fruit is preferred.  Tropic was planted at the following
densities:  one bay at 0.32 m2 (3.4 ft2)  per plant, three bays at 0.37 m2
(4 ft2), and one bay at 0.43 m2 (4.6 ft2).  Table 6 shows the yield per plant
for marketable grades No. 1 and 2.  As would be expected, a reduction in
plant density improved the per plant yield.  However, on a per bay basis, it
appears that either a lower density with a high yield or a high density with
a low yield produced about the same weight yield per bay.


       TABLE 6.   YIELD VS. DENSITY FOR TROPIC TOMATO - SPRING 1977

            Spacing                           Yield

     m2 (ft2)  per plant      kg (Ib) per plant      kg (Ib) per bay

     0.32        (3.4)       5.2       (11.5)       2176   (4798)
     0.37        (4.0)       5.6       (12.4)       2009   (4430)
     0.43        (4.6)       6.8       (15.1)       2138   (4714)
                               48

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SNAPDRAGONS

     This crop was grown because there are few local  cut snapdragon  producers
left, and there appeared to be a demand in the local  market.   This  projection
proved to be generally true except for the period between Thanksgiving and
Christmas when the demand was very low.  The crop was generally apportioned
into 50% white, 25% yellow, and 25% pink.  Seedlings  in group 3 flowering
classification included about 10% novelty (double flower, butterfly, bicolor)
for spring cutting.  All snaps were grown as single stem cuts as these gen-
erally had better stem and flower spike quality, were more uniformed and
flowered earlier.  Attempts to program the beds to flower in a sequential
order to insure a steady cutting supply proved unworkable.  No facilities for
photocontrol were available so the bed was cut when it had sufficient floret
count and replanted when empty.  The only significant problem encountered was
a tendency for boron deficiency to occur in the sandy soil.  The single layer
of Vexar nylon netting tended to shift horizontally when the plants reached
mature height.  Additional staking and tying of the netting helped solve this
problem.

ROSES

     Plants were  pinched at  1 cm  (0.4  in) diameter to  provide  a heavy yield
for  Valentine's  Day and Mother's  Day.  At other  times  selective pruning was
practiced  to  remove unproductive  and weak shoots.  During  June and  July  the
plants were pruned back to 2-3  of the  lowest  prominent buds  produced  over
the  previous  year to  control  plant height.  Marketable flowers were generally
cut  with two, five-leaflet leaves  left below  the cut.

     Night temperature  thermostat setting minimums were 15.6°C (60°F)  for
Cara Mia and  Golden Fantasie, and 16.7°C (62°F)  for  Sonia, Belinda  and  Coed.
The  day  maximum  settings were generally  5.5°C (10°F)  higher than the  night.

LETTUCE

      Discussions with potential buyers for this  product indicated  a prefer-
ence for looseleaf cultivars that could be used as salad components and
liners.  Grand Rapids H5-4 was  chosen because of its tip burn resistance and
Waldman's  for its dark green color appeal.   Several  beds of Summer Bibb were
planted  in August to  supply  a limited market.  All  varieties fared well
 through  the first crop, but  the second yield crop was reduced due  to a
 rhizoctonia infection.

 GERANIUMS

      Spinter type, F, hybrid geraniums, including Deep Red, Scarlet, Salmon,
 Snowdon Cheri, Heidi, Rosita and Ringo, were chosen for seed propagation.
 The night air temperature was maintained at 15.6°C (60°F) for the first 10
 weeks after  transplanting and then elevated to 18°C (65°F) until  sale.
 Table 7 shows the growing time required from seeding to first petal show.
                                      49

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              TABLE 7.  GROWING TO FLOWERING TIME - GERANIUMS

             Cultivar                         Weeks to Flower
             Heidi, Snowdon
             Ringo, Rosita
             Salmon, Cheri, Scarlet, Deep Red
                                        15
                                        16
                                        17
                          TABLE 8.  CROP YIELDS
Quantity Growing Yield Per
Sold Area Growing Area
Kg (lb) m2 (sq ft2) m2 (sq ft2)
11421 (25381) 1062 (11,424) 23.75 (2.22)
Crop
Duration
6 mo
 Crop

Tomato
1976
Tomato
1977          11605  (25791)

Leaf Lettuce   1557   (3460)

Snapdragons
Geraniums

Roses
  5489 bunches
  (w/bunch)

   6000 pots

113,082 bunches
(25/bunch)
929

437

494


139

410
(9,996)
(4,704)
(5,312)
27.6
7.8
11.1
(2.58)
(0.73)
(1.0)
Bunches
(1,500)    4218  (4 pots)

(4,410)   275.8   30.17
                Bunches
 6 mo

 6 mo

11 mo


 6 mo

24 mo
CONTAINERIZED TREE SEEDLINGS

     A bay of containerized tree seedlings was planted and maintained by
Bailey Nurseries, Inc., Newport, MN.  The soil was leveled, sprinkled and
compacted with a roller to obtain a fairly level, flat surface and covered
with a 4-mil sheet of clear polyethylene.  The planting consisted of 57,000
Mugho Pine (Pinus mugo). 2,000 Colorado Spruce (Picea punoens), 2,000 Black
Hills SpruceTPTcea glauca 'Densata') and 2,000 Austrian Pine (Pinus nigra).
The containers used were 32 cm (12.6 in) on a side with 100 cells per unit.
The cells measured 2.8 cm (1.1 in) diameter and 15 cm (5.9 in) deep.  These
were filled with a peat-perlite mix, seeded with 3-4 seed per cell and
covered with a 0.5 cm (0.2 in) layer of number 2 crushed granite poultry grit.
The containers were placed on the polyethylene sheet to prevent root pene-
tration into the soil and also to allow air pruning of any emerging root tips
through the bottom drain holes.  After emergence the cells were thinned to
two plants per cell, then two months later thinned to one plant per cell.
When the day length shortened to 12 hours, cool white standard 40-watt
fluorescent lights were used to extend the photoperiod to 24 hours.  The
light intensity measured from 2690 to 3770 lux (250-350 ft-c) at the container
surface.
                                     50

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     The seeds germinated well  and growth was vigorous except for December,
January and February.  No insect or disease problems were encountered.   The
containers were removed the latter part of May.   By this time the growing
medium was well root-bound and could easily be removed by simply pulling at
the base of the stem.  The average stem lengths  in May were as follows:
Mugho Pine 15.24 cm (6 in), Colorado and Black Hills Spruce 25.4 cm (10  in),
and Austrian Pine 28 cm (11 in).

     Two minor crops consisting of freesia (Freesia hybrida) and green bell
peppers (Capsicum Annuum) were grown for triaTTReitner crops fared very
well economically but growing conditions were adequate.

     No yield trials were conducted for the soil heating system since it was
impractical to implement a totally controlled situation where valid compari-
sons could be made.  It is intuitively felt, however, that the soil heating
was beneficial.  Verification of soil heating benefits can be obtained by
reviewing the  literature.

NURSERY STOCK

     A  propagation  trial of deciduous and  evergreen  ornamental  nursery stock
was conducted  from  November 1976 through June of  1977.   Hardwood  cutting
material was  rooted directly in the sandy  soil  using the soil heating system
for bottom heat  and the trickle irrigation tubing  as a  moisture source.  The
tops were hand misted.  Hardwood tree  seeds  were  also planted in  the  soil.
Most material  germinated and rooted very well.

     Removal  of  the material showed well  developed root systems.   Shoot
growth  rates  were very  rapid as would  be  expected in greenhouse conditions.

CONCLUSION

     The  cultural  practices  followed  in  the  greenhouse were, by and large,
standard  for  this  area.   From  a horticultural  standpoint, it was  felt that
the  most  advantageous  aspects  of this  heating system were the high air  flow
which  tended  to  reduce foliar  fungal  diseases and the soil  heating which
 improved  the  root  environment.

     This high air flow did  cause foliar burn in  the roses  during late  spring
when the  plants  were tall.  This problem could have reduced by  2.9 m (10 ft)
 gutter height instead of the 2.3 m (8 ft) used.
                                      51

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                           ECONOMIC FEASIBILITY


     A  stated goal of the Sherco Greenhouse project was to demonstrate the
 economic  feasibility of utilizing waste heat for greenhouse heating in
 Northern  climates.  In order to do so, careful attention was paid to cost
 throughout the project design, construction, and operation.  The data gathered
 during  the Sherco Greenhouse project, along with experience of commercial
 greenhouse operators who now utilize waste heat at Sherco, support the con-
 clusion that economic feasibility has been demonstrated.  In order to main-
 tain the  proper perspective, it should be remembered that only the economic
 feasibility of heating with waste heat has been proven.  That is, waste heat
 has been  shown to be competitive on a current cost basis with oil heat.  In
 making  the foregoing statement, it is assumed that the waste heat available
 in condenser cooling waters has no economic value as viewed by the utility.
 Furthermore, it is assumed that utilities are willing to sell waste heat to
 users at  their operating cost plus a reasonable return on investment to
 supply waste heat some distance from the power plant.  With these assumptions
 then, what remains to be proven is that it is economically feasible to re-
 locate a  vast greenhouse industry to selected power plant sites with suitable
 and reliable waste heat.  This will depend on a number of site and market
 related variables, but some of the most important considerations have been
 identified in this project and are addressed here.

 HEAT DELIVERY COST AND PRICING CONCEPTS

     The  cost to deliver heat from the condenser outlet of a power plant to
 greenhouse customers depends on certain general variables such as distance,
 total acreage served, pipeline design philosophies, etc. and some site
 specific  variables such as type of soil, climatic conditions, and method of
 connection to the cooling water system.  All of the information presented
 here is based on the site-specific characteristics of Sherco.  While it may
 be possible to generalize from this experience, generalization should be
made carefully with due consideration to the key variables that might differ
 from site to site.

     A 20.3 cm (8 in) tap and valve in a 183 cm (72 in) steel riser pipe at
 Unit I  tower was installed along with a 30.5 cm (12 in) diameter plastic
 pipeline, extending 1067 m (3500 ft) each way to the Sherco Greenhouse site
 and back  to the cooling tower basin in the summer of 1976.  The total cost
of this installation, which also included a 15.2 cm (6 in) plastic service
 line 30.5 m (100 ft) long from the main 30.5 cm (12 in) pipeline into the
 Sherco Greenhouse and interconnection with the greenhouse heating system,
was $84,000.   This pipeline was capable of delivering 101 1/s (1600 gpm)
 from Unit I riser pipe to the Sherco Greenhouse site.  The following summer


                                    52

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it was decided to expand the pipeline system to provide waste heat as  a
utility service to commercial  customers.   To do so,  a  35.6 cm (14 in)  tap
and valve were installed on a 183 cm (72  in) steel  riser at the Unit II
cooling tower.   This tap fed into a 45.7 cm (18 in) cast iron pipeline  that
went 305 m (1000 ft) each way to interconnect to the previously built  30.5 cm
(12 in) line.  Included in this construction also was  the cost of extending
the 30.5 cm (12 in) pipeline some 213 m (700 ft) one-way distance and  two
service connections with meters to two commercial greenhouse sites.  Also
included was the cost of an automatic chlorination injection system to
control pipeline bacterial fouling.  The total cost of this work was $141,000.
The new pipeline was intentionally oversized so that it could accommodate
future expansion of up to about 442 1/s (7000 gpm) with some additional  future
construction.  To date then, $225,000 has been invested in pipelines to serve
waste heat to present and anticipated customers.  Based on this experience
and engineering estimates of the cost to further expand waste heat service
for the 442 1/s (7000 gpm) initial development, a total investment in pipe-
lines of nearly $600,000, or about $43,000  for each .4 hectare (1 acre) is
projected.  Using this investment and typical utility financing, the  .4
hectare (1 acre) user must pay about $6,000-$8,000  per year for twenty years
to completely amortize the investment.  This  cost is the major cost of
serving waste heat  to the user, but fortunately, it is a  fixed cost once  the
investment is made.  After twenty years, continued operation of-the pipeline
should be possible,  in which case this large  fixed  cost would no  longer need
to be charged.

      In addition to the  capital investment  in pipelines,  there are operating
costs associated with the pumping energy required to deliver the  flow to  the
user  and return  it,  as well as the chemical cost for chlorination, and over-
all pipeline  network operation and maintenance.  The calculated  energy
required to deliver warm water about  1.2 km (4000 ft)  at  Sherco  amounts to
 .032  kwh/m3  (.12  kwh/1000 gal).  This  is based on low  pipeline velocities
that  will eventually increase, increasing the energy requirement  in the
future.  At current NSP  internal cost  for electricity,  the pumping energy
costs  .0484/m3  (.184/1000  gal).   For a typical  .4 hectare (1  acre)  plastic
greenhouse, the  pumping  energy would cost $270 per  year.   Chlorine for
bacterial slime  control  now costs  about  $550/year which prorates  to  .0444/m3
 (.167 4/1000  gal)..   Operating  labor and  maintenance will  be determined with
additional  experience,  but  the present allowance for other O&M is .1724/m3
 (.6534/1000  gal).   Actual  maintenance experience in the 1977-78  heating
season indicated a cost of .3544/m3 (1.344/1000 gal) which is considered
excessive but typical  of a first year of operation. Thus, the total  oper-
 ating cost  now stands at .2644/m3 (1.04/1000 gal) which works out to  about
 $1500 per year for a typical  .4 hectare. (1 acre)  greenhouse.

      The total  capital  and operating cost (experienced and projected) for a
 5.7 hectare (14 acre) complex  at Sherco  then amounts to about $9200 per year
 for a .4 hectare (1 acre) greenhouse.   On the basis of the annual energy
 required by the greenhouse, this amounts to a cost of $.96 GJ ($1.02/16*
 Btu.
                                     53

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     Several points are noteworthy concerning this calculated cost of waste
heat.   First,  this is the current cost, not a twenty-year average cost.  In
the future  cost escalation of pipeline O&M will cause this figure to rise,
though  a  doubling of the O&M cost would only increase the current cost by
16%.  Secondly, the calculated cost per unit energy required by the green-
house is  based on a calculated annual greenhouse heat loss of 9548 GJ/year
(9050 X 106 Btu/yr), which does not include boiler losses for comparable
useful  heat derived from combustible fuels.  And, finally, the instantaneous
heat extracted from the waste heat source is based on a AT of 8.3°C (15°F),
which is  only half of the available heat in the waste heat stream since the
power plant condenser temperature rise is 16.1°C (29°F).  It would be possible,
therefore,  in some applications to reduce the unit cost of heat by achieving
a higher  AT in the greenhouse heating system.  This assumes, of course, that
waste heat  is sold on the basis of cost of delivery of warm water and not on
the basis of value of heat extracted by the user.

     The  latter possibility suggests that the philosophy adopted by utilities
for waste heat pricing can impact the economic feasibility.  The impact,
whether adverse or beneficial, depends obviously on the philosophies adopted.
NSP has decided to attempt to price the first units of waste heat sold on a
projected future average cost of serving a defined, in this case 5.7 hectare
(14 acre),  complex of greenhouses.  What this means is that the return on
investment  deemed acceptable by NSP will not be achieved until the pipeline
network installed is fully utilized.  The early year losses are initially
sustained as part of the development cost of commercializing the concept, but
hopefully will be recovered later after the pipeline network is fully
amortized.  This pricing philosophy is promotional  in that it provides
service at  less than cost for the number of years it takes to fully develop
the installed pipeline system.  However, the price signal is realistic since
it reflects expected future costs so that large increases in price need not
occur in the future.

     In addition to the general  cost of service pricing philosophy, NSP has
decided to offer waste heat to commercial  users on the basis of long-term,
fixed-price contracts.   These contracts, currently offered for ten-year
periods, are seen as mutually beneficial to NSP and the greenhouse operator.
They benefit NSP because of take or pay provisions that guarantee repayment
of the large fixed costs associated with the waste heat service, and they
immensely benefit the greenhouse operator because energy costs are no longer
subject to arbitrary price changes or general inflation.  While only the
fixed cost of service (i.e., pipeline investment cost) is covered by these
contracts, this still  stablizes energy cost for the grower because fixed
costs are over 80% of the cost of serving waste heat.

     The current NSP pricing philosophy has been implemented in the form of
a demand and use rate structure for waste heat, or warm water service as it
is called.  The demand portion of the rate now stands at $3.42/l/min ($12.95/
gpm) of peak average 15-minute flow recorded by NSP on the customer premises
during an entire heating season.  The use portion is now .264
-------
rate which reflects fixed costs  will  be held constant  for the  ten-year
duration of the service agreement contract.   After ten years the  demand  rate
offered for contract renewal  will be  that prevailing in  the year  of  renewal.
During the period of the service agreement,  the variable use charge  will  be
changed yearly according to cost of service  data.

HEAT EXCHANGE SYSTEM COST

     In order to utilize low temperature condenser waste heat, greater heat
transfer surface areas and larger volumes of heated air  must be distributed
than in conventional greenhouse heating systems.  Obviously, this produces
an increase in the cost of the heating system, initially, and  in  the cost of
operating the system due to the increased electric energy requirements.

     The actual capital costs for all air heating system materials delivered
to the Sherco Greenhouse in mid  1975 was $46,662 or $21.98/m2  ($2.04/ft2).
Table 9 presents a breakdown of  the actual cost for Sherco along  with an
estimate for a .4 hectare (1 acre) commercial greenhouse facility in 1977
dollars.  The materials include  everything needed for the complete erection
of the air heating system and water circulation system including all sheet-
metal, dampers, ducts, piping, valves, fittings, flowmeters,  wiring, and
controls.  In the case of the estimate for a commercial  facility, a complete
back up heating system is included in the cost estimate.  The reduction in
cost for the commercial system compared to Sherco results from design im-
provements that were made as a result of the Sherco experience.  It should be
noted that the costs presented do not  include a soil  heating  system which  is
not considered a necessary, though perhaps a desirable, part  of the basic
waste heat heating system.


                       TABLE 9.  WASTE HEAT SYSTEM

                 Materials Cost  Summary  (Actual Dollars)

                                                                Estimated
                                             Sherco Greenhouse  Commercial
                                                 Actual1        Greenhouse2
                                                 Mid  1975         Mid 1977

      Fan  Coil  Units  and  Accessories               21,656            47,000
      Circulating Mater Pumps,  Piping,
        and Valves                                  6,764             5,000
      Electrical  and Controls                      18,242            11,000
      Back Up Heaters and Fuel  Storage               -              11,000
                              TOTAL               46,662            74,000
                              $/m2                  21.98             18.59

      Sherco Greenhouse Area = 2123  m2 (22,848 ft2)
      2Commercial  Greenhouse Area = 3980 m2  (42,840 ft2)
                                     55

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     The cost to install the waste heat system was not specifically separated
from the total labor cost to erect the entire Sherco Greenhouse facility.
However, because of the highly prepackaged nature of most of the heating
system equipment, it is believed that installation labor would not exceed 25%
of the total heating system materials cost.  While this percentage may seem
low, it should be considered that an entire greenhouse can be erected for
about $10.76/m2 ($l/ft2).  And, 25% of the heating system materials cost
amounts to $4.52/m2 ($.42/ft2) of greenhouse floor area.  In addition, recent
commercial experience has shown that an entire waste heat greenhouse facility
could be erected for little more than $6.56/m2 ($.61/ft2) labor cost, exclud-
ing electrical work and some other minor subcontract items.  Using an esti-
mated installation cost of 25% of total materials yields a total investment
of about $92,500 for a .4 hectare (1 acre) greenhouse complete waste heat
system.  This figure must then be compared to the cost of the conventional
heating system displaced.  Estimates vary from about $10.26 - 21.52/m2
($1.00 - 2.00 ft2) of heated floor area for the Minnesota climatic conditions.
Using the mid-range of the estimates, a conventional heating system serving
a .4 hectare (1 acre) greenhouse would cost about $65,000.  The apparent
capital cost difference between a conventional system and the waste heat
system is about $27,500 for the .4 hectare (1 acre) unit.  This differential
capital investment must be amortized over the life of the heating system,
which is believed to be 20 years, and considered as an added cost of owning
and operating the waste heat system.

OPERATING COST COMPARISON TO CONVENTIONAL SYSTEMS

     The operating costs for a greenhouse facility using waste heat depend on
the price charged for waste heat, the availability and temperature of the
waste heat, the cost of electricity to operate the heating system, and the
cost of backup or supplemental fuel.  During the operation of the Sherco
Greenhouse Project, accurate records were kept and the cost of all elements
are known.  However, because the Sherco Greenhouse heating system was designed
before the cost of waste heat was known, it probably uses a higher peak flow
rate than can be justified on a commercial basis.  The Sherco Greenhouse uses
the same total flow for air and soil heating as does a commercial facility
which is almost twice as large.  However, the commercial greenhouse was de-
signed when the cost of waste heat was known.  Therefore, the operating
experience and projections based on the commercial facility are presented here.

     The comparative operating costs of utilizing waste heat versus conven-
tional  heating are indicated in Table 10.  The figures presented are based on
a .4 hectare (1 acre) double plastic greenhouse located at the Sherburne
County Plant site.  The total operating costs on an annual basis for the
waste heat system in 1978 are estimated to be $17,000 which includes $8,000
for waste heat, $7,000 for electricity, and $2,000 for standby propane.

     A typical conventional greenhouse using No. 2 fuel oil has an estimated
heating cost of $28,000 per year.  There is an apparent savings of $11,000
per year by utilizing the waste heat system in 1978 dollars.  But, the big
advantage of the waste heat system is more apparent in the future as fuel
costs escalate.  The waste heat system would realize an escalation in the
cost of propane and electricity, but the waste heat costs would not increase

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very much due to the fact that the pipeline investment had been made 20 years
previously.  In 1998, at a compound escalation of 6% for all  utilities and
variable operating costs, the waste heat system shows a cost advantage of
$51,000 per year.  These comparative operating costs are projections based
in part on operating experience and anticipated operating experience at the
Sherco site.

     The actual operating costs for all utilities for the .4 hectare (1 acre)
commercial floral range totaled $3.98/m2 ($.37/ft2) for the period November-
May.  This compared to $7.00/m2 ($.65/ft2) for a glass greenhouse owned by
the same company.  While part of the savings is attributable to the fact that
one greenhouse is double polyethylene and the other is glass, probably only
30% of the savings results from that difference.  The remaining savings,
about $.86/m2  ($.08/ft2), directly result from the use of warm water for
heating.  This actual experience in the first year of commercial operation of
the warm water heating system falls considerably short of the projected annual
savings of roughly $11,000 for a .4 hectare (1 acre) unit, but the greenhouse
with which the comparison was made received 62% of its energy as interruptible
natural gas.   Had the other greenhouse been heated only with oil, the  compara-
tive savings would be about $13,000.


            TABLE 10.  COMPARATIVE OPERATING  COSTS OF WASTE HEAT
                              VERSUS CONVENTIONAL HEATING

                              - 1978 Costs  -              -  1998 Costs  -
                         Waste Heat  Conventional   Waste Heat  Commercial

      Fuel  Cost
       Standby Propane     2,000                       6,000
       #2  Fuel  Oil                     31,000                     95,000

      Electricity          8,000        1,000          26,000       4,000

      Waste Heat Cost      8,000       	         10,000      	

         Total  Per Acre
         Per Year          18,000       32,000          42,000      99,000


                Basis:   12 Fuel  Oil  @ $.45/gal
                        Propane Cost @ $.43/gal
                        Electricity Cost @ $.035/kwh
                        Escalation @ 6%


      In terms of overall commercial acceptance of waste heat, there are other
 considerations that are very important.  One of these is the distance from
 the market.  Most new electric power stations are located some distance from
 major metropolitan centers for reasons of air quality and other considera-
 tions.  Therefore, the source of waste heat is not close to the market for
 greenhouse products.  The increased transportation costs must be considered

                                       57

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by the prospective greenhouse operator in determining whether he can relocate
to a power plant site to use waste heat.  A second consideration is the cost
of land and the manner in which land acquisition is handled.  At Sherco, NSP
owns all of the land adjacent to the power plant.  The land on which the
commercial greenhouses are located is leased land.  Therefore, they will
never benefit from the appreciation in land values which in the past has
generated significant long-term capital gains for greenhouse owners.  Thus,
in cases where land will be owned by a utility and leased to greenhouse
operators, significant savings in operating costs are necessary to offset the
disadvantage of leased land.   Another consideration may be the local property
tax structure.  Generally speaking, the value of a power station impacts
local property tax rates to the extent that property taxes tend to be low in
areas in which power plants are located.  This can have a beneficial effect
on the commercial  greenhouse operation.

     While it appears economically feasible to provide waste heat service to
greenhouse customers and it appears reasonable for the greenhouse customers
to make additional investments in heating systems to save in future heating
costs, it is still too early to predict whether this trend will hold true at
many power plant sites in the U.S. or whether this will prove to be a
relatively unique  situation.
                                    58

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                                Appendix A

                                 BACKGROUND


     Northern States Power Company began its investigation of beneficial use
of waste heat from its power plants in 1970.  At that time, all  of the
Company's generating facilities employed once-through cooling.  Some of the
plants used "helper" cooling towers to meet thermal effluent standards.
However, none of the stations were operated on a closed-cycle basis.

     A nuclear plant under construction at that time near Red Ming, Minnesota
(Prairie Island) was designed for closed-cycle operation.  A coal-burning
plant in Sherburne County, also closed-cycle, was on the drawing board.  The
warmer temperatures expected from closed-cycle design encouraged research
engineers at the Company in their efforts to investigate waste heat appli-
cations.

     The Agricultural Experiment Station of the University of Minnesota was
invited in December, 1970, to participate in discussions concerning the
waste heat problem.  Possible agricultural enterprises where warm water might
be economically attractive were suggested.  The response from University
scientists was enthusiastic.  From that time on, the Company and the Univer-
sity worked in a close partnership to explore all possibilities.

     The University formed two three-man teams comprised of agricultural
engineers, horticulturists and soil scientists to study along with others at
the University, at NSP and elsewhere, the best ways to use the then unused
heat in the cooling water.  NSP provided financial support for the study.

     It soon was evident that  little use could be made of the warm water from
the once-through cooling generating plants.  Discharge water temperatures in
winter when  it could be used for  heating were approximately  10°C (50°F). or
about the permitted 10°C  (18°F) above the ambient temperature of the Intake
water at 0°C  (32°F).  Most heating applications for enclosed plant  production
or residences required temperatures of  15.5eC-21.1°C (60°-70°F).  Even use
for soil heating showed little  promise  because few crops grow well  at  temper-
atures of 10°C  (50°F) or  lower.   Frost  protection was considered but soon
rejected because water droplets cool to ambient air temperature  if  they
travel 4.6-6.1 meters (15-20 ft)  through the air.  The main  consideration  in
frost protection is the release of heat, 334,934 KJ/kg (144  Btu/lb), by the
water as it  changes state  from liquid to solid,  I.e. to  ice.

     The review of heating requirements for various  applications and the
projection that all,  or nearly all, future  steam electric generating plants
would operate on a "closed-cycle" basis eventually led  to the warm water
greenhouse  project.   NSP's closed-cycle designs  called  for condenser d1s-


                                     59

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charge temperatures of no less than 29.4°C (85°F).  If water temperature re-
ductions during delivery from condensers to the use point could be limited to
0.5-1.7°C  (1-3°F), then an operating differential between the source water
and the use environment of 5.5°C-11.1°C (10°-20°F) could be expected.  It
appeared that adequate heat transfer could take place for heating structures,
if equipment were properly sized and operated.

     Some of the research projects and demonstration work studied by the
teams of University agricultural scientists included:

     (1)  The Environmental  Research Laboratory, University of Arizona
          and its "total  energy" pilot study at Puerto Penasco, Mexico

     (2)  Oak Ridge National Laboratories greenhouse work led by
          Dr. Sam Beall and William Furlong

     (3)  Commercial  vegetable greenhouses in Cleveland, Ohio and
          Houston, Texas

     (4)  Wright Roses, Cranbury, New Jersey

     (5)  Eugene Water and Electric Board, Eugene, Oregon

     (6)  Federal  Water Quality Laboratory, Corvallis, Oregon

     (7)  Dr. L. L.  Boersma, Oregon State University

     (8)  TVA, Muscle Shoals, Alabama

     Most of these visits and preliminary studies took place in 1972 and
1973.

     It was at this  time  that a joint decision was made by NSP and the
University of Minnesota to seek financial  support from the U.S. Environmental
Protection Agency for a greenhouse demonstration.

     The objectives  of the project were:

(1)  Utilize energy  that  is  being wasted as a basis for an overall program
     to conserve natural  resources.

(2)  Demonstrate methods, using readily available equipment, of economically
     and reliably heating and managing a greenhouse with waste warm water
     from the condenser of a power plant.

(3)  Encourage private operators to build their own greenhouse at the power
     plant site to take advantage of a low-cost form of energy.

(4)  Determine the costs  and problems associated with building, operating,
     and maintaining a warm water supply and return pipeline at a multi-
     unit plant.
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     Early in the development of the greenhouse waste heat project, consider-
ation was given to the use of power plant warm water for cooling purposes as
well as heating.  It was reasoned that if cooling a structure with warm water
proved to be practical, greenhouses could be used as supplementary horizontal
cooling towers.  This concept was investigated in a pilot project which will
be described later in this report.

     One of Northern States Power Company's stated goals:  "To contribute
to the quality of life where we serve by:  (1) demonstrating active steward-
ship of the environment and of the use of natural resources, and (2) sharing
our varied corporate resources with those who need help" was accomplished by
this project.

     The NSP Sherburne County Generating Plant  (Sherco), located 45 miles
northwest of the Twin Cities, was the site selected for the project.  Sherco
Is a two-unit coal-fired plant with a total rated output of 1360 NW.  It has
closed-cycle mechanical draft wet cooling towers for thermal pollution control
and a  limestone scrubber system for air pollution control.  The first unit
began  commercial operation in May, 1976, with the second unit going on line
in May,  1977.  The condenser cooling water flow rate for each unit 1s 15.77
m3/s (250,000 gpm) with a design  cooling water  temperature differential, AT,
of  16.1°C  (29°F).  The winter design minimum temperature of the water at the
condenser  outlet 1s  29.4°C (85°F).  This 1s the design  temperature of the
warm water for the greenhouse heating system.

     The Company owns more than 1200 hectares  (3000  acres) of land adjacent
to  the power plant.  Space has been allocated  for:   (1)  a greenhouse develop-
ment,  (2)  a 137 hectare (340 acre) University  Sand  Plain Agricultural Ex-
periment Station Farm  and  (3) an  Industrial park.

     The soil  in the area  is a  loamy, coarse  sand,  and  the topography Is
nearly level.   Excellent drainage conditions  permit greenhouse  construction
without  drain  tiles.   The  soil  conditions  and topography make the Install-
ation  of warm water  supply and  return pipelines connecting the  greenhouse
to  the power plant relatively easy.

       In 1973,  with  the energy  crisis beginning to surface,  the emphasis on
waste  heat projects  began  to shift from thermal pollution control  to energy
utilization and conservation.   It was becoming Increasingly  difficult  to
justify, economically, construction of  greenhouses at power  plant sites  in
sufficient numbers  to significantly reduce thermal  pollution.   For example,
 It  would require 405 hectares  (1000 acres) of greenhouses  to use the  heat
 rejected by a  1000 MW plant  under conditions  of operation at the Sherco
 plant.
                                      61

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                                 Appendix  8

                               PILOT PROJECT
     While the application for EPA funding was pending, NSP, with the Univer-
sity's commitment of technical assistance, developed a small pilot project to
"prove the concept" of heating greenhouses with waste heat in a northern
climate.

     Previous research work conducted in the U.S. had concentrated on using
evaporative cooling pads with saturated air to provide both latent and
sensible heat transfer for greenhouse heating.  In this research work, it
had been found that high humidity occurred in the greenhouse itself; there-
fore, the potential existed for increased disease problems in similarly
heated greenhouses.  In addition, the difference in climate in Minnesota
compared to Southern states where the other greenhouse research work was
being conducted suggested that a heating system design suitable in one area
might not be suitable in another.

     Because of the considerable concern regarding whether an evaporative
approach would work, it was decided to design a dry finned-tube heat exchange
system of sufficient size to transfer the required heat from 29.4°C (85°F)
water to heat a 204 m2 (2,200 ft2) greenhouse which was owned and operated
by a commercial florist in Minneapolis.  In addition to the finned-tube
system, an evaporative system was installed in series to allow total flexi-
bility of operation for either heating or cooling with the evaporative
system, heating only with the dry finned-tube, or heating with both the
evaporative system and the finned-tube system.  In addition, the pilot
research greenhouse heating system was designed to operate in a constant
heat rejection mode.  Outside air could be introduced automatically so that
the heat exchange equipment had a constant inlet air volume and temperature
and a constant inlet water volume and temperature.  Thus, a constant heat
load would appear on the heating system regardless of the actual heat demand
of the greenhouse.

     The pilot research greenhouse was designed in the fall of 1973 and put
into operation in the spring of 1974.  The greenhouse was operated in the
heating mode in March, April and May of 1974, and evaporative cooling tests
with warm water were run in the summer of 1974.  Additional heating system
tests were run in the winter of 1974-75.  As a result of the operating ex-
perience in the pilot research greenhouse, it was concluded that using very
warm water, up to temperatures of 46.1°C (115°F) on an evaporative cooling
pad, resulted in no measurable sensible cooling of the ventilation air for
the greenhouse.  While large heat rejection rates could easily be achieved,
there was no particular benefit to the greenhouse, since the resulting
greenhouse temperature (but not humidity) could have been achieved just as


                                     62

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easily by mechanical  ventilation only.   As a matter of fact,  a more satis-
factory environment could be achieved by using recirculating  well  water (at
lower temperature than warm condenser water) on an evaporative cooling system
rather than trying to reject waste heat.

     The heating experiments, on the other hand, revealed that the 29.4°C
(85°F) warm water source temperature was adequate to maintain greenhouse
temperatures above 12.8°C (55°F) throughout the 1974-75 winter heating
season.  It was tentatively concluded at that time that the required area of
finned-tube heat exchanger was not excessive for installation directly in
the greenhouse, but that the fan power requirement was relatively high.  It
was also concluded that temperature drops of more than 10°C (18°F) would be
very difficult to achieve with finned-tube exchangers without adversely
affecting the internal air temperature of the greenhouse.  It was further
concluded, based on rather limited tests of direct evaporative heating of
the greenhouse, that the resultant fogging and high humidity conditions
would not be acceptable to commercial floral operators.  It should be re-
membered that the research work reported was conducted in an existing
commercially-owned and operated greenhouse, so there was not complete freedom
to conduct tests that would result in conditions  in the greenhouse considered
adverse to the production of a commercial crop.   Nevertheless, the overall
conclusion of the pilot research project was that waste heat properly utilized
with  finned-tube heat exchanger systems could  create  an environment  that was
comparable with that obtained with other heat  sources currently used  in the
greenhouse Industry.  It was believed that  such  a system could be designed,
installed, and operated at a cost that might be  competitive with  the  cost  of
alternative fuels in the future.

      It was also concluded that the  notion  of  a  constant heat rejection rate
permitting greenhouse functioning as a  horizontal cooling  tower for  the
power plant was  impractical since it required  continuous operation of a fan
and  air handling system  considered to be  an excessive energy  consumer in  the
first place.  This consideration  [in conjunction with the  considerations  that
it would  take more than  405  hectares  (1000  acres) of  greenhouses  to  reject
all  of the  heat  from  a  1000  MW  power station and that evaporative cooling
with waste  heat  from  a  power plant  provided no particular  benefit for the
greenhouse] suggested that  the  idea  of  greenhouses replacing  cooling towers,
perhaps,  could  and should  be set  aside  until  such time  as  the basic  concept
of utilizing waste heat for greenhouse  heating could  be demonstrated to be
commercially viable  and of commercial  interest.   From this experience,  then,
the  foundation  was  laid for the development of the more commercialized  system
designs  utilized in  the Sherco  Greenhouse project.
                                       63

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en
                                                            jjSfiMi'iiii*1.-
                                 Figure 27  Sherco Power Plant and Greenhouse Complex

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                               TECHNICAL REPORT DATA
                         (Please read Instructions on the reverse before completing)
 REPORT NO.
E£A-600/7-80-099	
 'TITLE AND SUBTITLE
  Demonstration of Beneficial Uses of Warm Water
from Condensers of Electric Generating Plants
                                                     3. RECIPIENT'S ACCESSION NO.
                             6. PERFORMING ORGANIZATION CODE
                             . REPORT DATE
                             May 1980
 AUTHOR(S)L.L.Boyd (U. of MN),G. C.Ashley,
 . S. Hietala,R. V. Stansfield, and T. R. C. Tonkinson
                                                     8. PERFORMING ORGAN 12 AT ION REPORT NO.
 PERFORMING ORGANIZATION NAME AND ADDRESS
Northern States Power Company.
414 Nicollet Mall
Minneapolis, Minnesota  55401
                             10. PROGRAM ELEMENT NO.
                             EHE624
                             11. CONTRACT/GRANT NO.

                             Grant S-803770
 2. 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
                             Grant Final; 5/75-4/80
                             14. SPONSORING AGENCY CODE
                               EPA/600/13
15. SUPPLEMENTARY NOTES IERL_RTpject officer jg Theodore G. Brna, Mail Drop 61,
919/541-2683.
is. ABSTRACT
              report gives results of a project to demonstrate that warmed cooling
water from condensers of electric generating plants can effectively and economically
heat greenhouses.  The 0.2-hectare demonstration greenhouse, at Northern States
Power Co. 's Sherburne County (Sherco) Generating Plant,  used 29.4 C water to heat
Doth air and soil: finned-tube commercial heat exchangers  were used to heat the air;
and buried plastic pipes , the soil.  Warm water from the Sherco 1 cooling tower was
piped over 0. 8 km  to the greenhouse where it was  cooled from 2. 7 to 5. 6 C before
returning to the cooling tower basin. Roses and tomatoes were the principal crops
in the 3-year test,  although other flowers and vegetables,  and conifer seedlings
were also grown. The warm water heating system supplied all the greenhouse heating
requirements, even at ambient temperatures as low as  -40 C. Roses, snapdragons,
 eraniums , tomatoes,  lettuce, and evergreen seedlings were grown successfully.
The demonstration proved the concept to be both technically and economically feas-
ible at Sherco, with an apparent saving of S"4500/hectare in 1978 dollars over fuel oil
heating, plus an  annual oil savings of about 500 cu m/hectare. Privately financed
commercial greenhouses heated with warm water were built  at Sherco in  1977. The
commercial greenhouses will expand from 0.48 to almost 1 hectare by late 1980.
 7.
                             KEY WORDS AND DOCUMENT ANALYSIS
                DESCRIPTORS
 Pollution
 Electric Power Plants
 Cooling Water
 Greenhouses
 Heating
 Vegetables
 Flowers
Softwoods
Seeds
                                          b.IDENTIFIERS/OPEN ENDED TERMS
                                         c.  COSATI Field/Group
Pollution Control
Stationary Sources
Conifers
Seedlings
13B
10B
13A
02 C
13H
02 D
11L
 13. DISTRIBUTION STATEMENT
  Release to Public
                                          19. SECURITY CLASS (This Report/
                                          Unclassified
                                          21. NO. OF PAGES
                                                  73
                                          20. SECURITY CLASS (This page)
                                          Unclassified
                                          22. PRICE
 EPA Form 2220-1 (9-73)
                                        65

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