EPA 600/7-81-034
March 1981
GREENHOUSE PRODUCTION OF
BEDDING AND FOLIAGE
PLANTS WITH INDUSTRIAL HEAT
by
I. J. Crumbly
Fort Valley State College
Fort Valley, GA 31030
IERL-RTP-1047a
EPA 600/D-80-014
EPA Project Officer T. J. Brna
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
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ABSTRACT
Potential beneficial use of industrial waste heat for the production
of bedding and foliage plants was evaluated via use of conventionally and
warm water heated greenhouses in Fort Valley, Georgia. Each greenhouse
was 9.1 m X 21.9 m (30 ft X 72 ft) and a plastic covered quonset. The
research greenhouse was heated and cooled using simulated warm condenser
cooling water, while the control greenhouse had conventional heating and
cooling in the 9-month test program. During 1979, cultivars of 10 leading
ornamental bedding plants, 8 species of foliage plants, and tomatoes as
bedding plants were studied for growth rate, survivability, time of
flowering, and susceptibility to disease in the humid greenhouses.
No statistically significant difference in growth rate for 7 of 10
ornamental and 2 of 8 foliage plants was observed in the two greenhouses.
Tomatoes, coleus and geraniums grown in the conventional greenhouse had
statistically significant higher growth rates. Syngonium podophyllum
and Philodendron pertussum grown in the waste heat research greenhouse
had statistically significant higher growth rates. Ornamental bedding
plants grown in the conventional greenhouse flowered approximately 7.6
days earlier. No significant difference in survivability among foliage
plants and 8 of 10 ornamentals was seen in either greenhouse. Browallia
and coleus survived better in the conventional greenhouse. No diseases
were evident in either greenhouse.
Heating and cooling of the waste heat research greenhouse was
satisfactory, despite the fin-tube heat exchanger being oversized for
the available warm water flow. Environmental control was adequate; at
no time was condensation observed on the foliage of plants grown in
either greenhouse. Preliminary economics indicate that industrial
waste heat can be an attractive alternative to natural gas and fuel
oil for greenhouse heating.
DISCLAIMER
This report has been reviewed by the Industrial Environ-
mental Research Laboratory (RTF), U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the views
and policies of the Agency, nor does mention of trade names
or commercial products constitute endorsement or recommen-
dation for use.
11
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TABLE OF CONTENTS
Page
Abstract i j
List of Figures v
List of Tables vi
List of Abbreviations vii
Acknowledgements viii
SECTION 1. INTRODUCTION 1
BACKGROUND 1
OBJECTIVES 2
A DESCRIPTION OF THE RESEARCH FACILITIES 3
SECTION 2. CONCLUSIONS 7
HORTICULTURAL 7
ECONOMIC 8
ENGINEERING 8
SECTION 3. RECOMMENDATIONS .,.. 10
SECTION 4. HORTICULTURAL STUDIES 11
BEDDING PLANTS H
DRY WEIGHTS (THE WHOLE PLANT) 11
DRY WEIGHTS (AERIAL PLANT PARTS) 13
FLOWERING DATES IN PAKS AND POTS 14
SURVIVAL RATE 15
FOLIAGE PLANTS 16
DRY WEIGHTS (AERIAL PLANT PARTS) 16
SURVIVAL RATE 17
SECTION 5. GREENHOUSE PERFORMANCE 18
HEATING 19
COOLING 24
RELATIVE HUMIDITY 28
iii
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Page
SECTION 6. ECONOMIC APPROACH AND MARKETING STUDIES 31
ECONOMIC APPROACH 31
CONSTRUCTION COST 31
BASIC COST (MATERIALS) 31
BACK-UP HEATING SYSTEM 32
GREENHOUSE ENERGY REQUIREMENTS 34
CURRENT COST FOR ENERGY 34
COST FOR FOSSIL FUEL 34
PROJECTED COST OF WASTE HEAT 35
PROJECTED SAVINGS BY USING WASTE HEAT 35
MARKETING STUDIES 37
BEDDING PLANTS 37
FOLIAGE PLANTS 37
POTTED CHRYSANTHEMUMS AND POINSETTIAS 38
ECONOMIC INCENTIVE TO USE WASTE HEAT 38
REFERENCES 39
IV
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LIST OF FIGURES
Page
1 A schematic representation of the waste heat
research greenhouse 5
2 A schematic representation of the conventional
greenhouse 6
3 The arrangement of bedding plant species in the
waste heat research greenhouse 12
4 Average low night air temperature from
February 1 through February 24, 1979 20
5 Average high daytime air temperature from
February 1 through February 24, 1979 21
6 Comparative air temperature history of 24-hour
period in the waste heat research greehouse
during an ice-snow storm on February 18, 1979 .... 22
7 Comparative air temperature histories over a
four-day period in January, 1979 23
8 Average high greenhouse temperatures with water
heated to 43.loc (109.6°F) in the waste heat
research greehouse from July 1 through July 4,
1379 25
9 Comparative cooling during 24-hour cycles
between waste heat greenhouse and conven-
tional greenhouse using water heated to 43.1°C
(109.60F) 26
10 Average high temperatures reached in green-
houses using water heated to 51.2°C (I24.6°F)
in the waste heat research greenhouse
simulating the temperature of effluent water
from a closed cycle plant (August 14-17, 1979) 27
11 Potential for sensible heat exchange from effluent
water to air during evaporative cooling in the
waste heat research greenhouse from August 29
through September 3, 1979 29
V
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LIST OF TABLES
Table Page
1 MEAN DRY WEIGHT (g) OF 8 WHOLE PLANTS/REPLICATION,
APRIL 1, 1979 . . 13
2 SPRAY DATES OF B-NINE GROWTH RETARDANT ... 13
3 MEAN DRY WEIGHT (g) OF 20 AERIAL PLANT PARTS/
REPLICATION, APRIL 12, 1979 . . . 14
4 FLOWERING DATES OF BIDDING PLANTS IN PAKS 15
5 MEAN SURVIVAL RATE BASED ON 4 FLATS/REPLICATION
(128 PLANTS), APRIL 10, 1979 15
6 SPECIES AND CULTIVARS . . . 16
7 MEAN DRY WEIGHT (g) OF AERIAL PLANT PARTS,
AUGUST 23, 1979 16
8 MEAN DRY WEIGHT (g) OF AERIAL PLANT PARTS,
SEPTEMBER 19, 1979 17
9 MEAN SURVIVABILITY BASED ON 100 PLANTS/REPLICATION,
AUGUST 23, 1979 17
10 AVERAGE MONTHLY TEMPERATURE OF EFFLUENT WATER AT
BROWN'S FERRY NUCLEAR POWER PLANT LOCATED IN NORTH
ALABAMA is
11 PERCENT RELATIVE HUMIDITY WITH EFFLUENT WATER
TEMPERATURE SET AT 51.7°C (i25.0°F) 30
12 COMPARATIVE CONSTRUCTION COST BETWEEN THE CONVEN-
TIONAL GREENHOUSE AND THE WASTE HEAT GREENHOUSE
WITHOUT BACK-UP HEATING SYSTEM ....... 33
13 PROJECTED COST OF BACK-UP HEATING SYSTEM WITH AN
OUTPUT OF 4.5 GJ/HR/.4 HECTARE (4.3 MBTU/HR/ACRE). ... 33
14 A PROJECTED COMPARATIVE CONSTRUCTION COST BETWEEN A
CONVENTIONAL GREENHOUSE AND A WASTE HEAT GREENHOUSE
BASED ON .4 HECTARE (1 ACRE) BACK-UP HEATING SYSTEM . . 34
15 ESTIMATED POTENTIAL ANNUAL SAVINGS IN ENERGY COST
USING THREE PRICES FOR WASTE HEAT COMPARED TO
NATURAL GAS AND NO. 2 FUEL OIL AND THE NUMBER OF
YEARS REQUIRED TO BREAK EVEN 36
VI
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LIST OF ABBREVIATIONS AND SYMBOLS
ABBREVIATIONS
Btu
°C
OF
ft
gal
gal /mi n
Gj
g
hr
in
I
1/min
1/s
Mj
MW
m
m/s
mph
MBtu
No.
Tj
British thermal unit
degrees Celsius
degrees Fahrenheit
foot
gallon
gallons per min
gigajoules (one billion joules)
gram
hour
inch
liter
liters per minute
liters per second
megajoules (one million joules)
megawatt
meter
meters per second
miles per hour
million British thermal units
number
square foot
square inch
square meter
terajoules (one trillion joules)
Vll
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ACKNOWLEDGEMENTS
The author would like to give thanks to Dr. Gerald Williams,
Dr. Porter Russ, Dr. Earl Burns, Dr. Johnny Carter, Mr. Carl Madewell
and Mr. Robert Pile of the Tennessee Valley Authority for their
support and cooperation. From Fort Valley State College, the author
is appreciative to Mr. Merchant E. Singleton and Dr. Robert Steele
for their technical assistance and to Ms. Clara Tarver and Mrs
Consiwilla Cobb Studstill for their clerical help. The author'also
wishes to thank Dr. Theodore G. Brna of the Environmental Protection
Agency for his suggestions in preparing the manuscript herein.
Vlll
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SECTION 1
INTRODUCTION
BACKGROUND
Water is used in the power plant industry for cooling purposes and
energy added to this water is described as waste heat. In the past,
the normal procedure has been to dump discharged cooling water coming
from power plants back into rivers, lakes and cooling ponds where the
energy added is dissipated. Most recently, to prevent adverse environ-
mental impacts of waste heat and to prevent large water withdrawals
associated with harm to aquatic life, the power plant industry has been
forced to build expensive cooling towers.
If means can be developed so that this warmed water could be
utilized to heat and cool greenhouses and extend the growing season of
certain horticultural and field crops, it would help conserve energy
while improving water quality. Three other advantages are (1) a normal
waste product would have economic potential to the power plant, (2) a
reduction in the cost of crop production could be passed on to the
consumer, and (3) the country would realize a slight-to-moderate reduction
in thermal pollution depending on size, kind of industry and location.
The Environmental Protection Agency estimates that the U. S. will
require approximately 757 billion liters (200 billion gallons) of fresh
water daily to cool the condenser steam of power plants required to
produce the thousand billion kilowatt hours needed annually by 1980 (2).
Such water will be essentially free of contaminants, and it will be
discharged at 29° to 49°C (85° to 120°F).
The annual quantity of waste heat presently available in the U. S.
is approximately 10,500 quadrillion joules (10 quad* Btu) equivalent to
254 gigaliters (1.6 billion barrels) of fuel oil (8). This represents an
annual amount of energy slightly less than 20% of all the energy used
annually in 1971. However, this is a low-grade (low temperature) form of
energy, and opportunities to use it beneficially are limited. Within
30 years, the electrical power industry will require the disposal of
about 21 quadrillion joules (20 trillion Btu) of waste heat per day (6),
One nuclear power plant having a 1,000 MW capacity can supply enough waste
heat to accommodate 400 hectares (1,000)acres of conventional greenhouses
Greenhouses require large amounts of energy to maintain adequate
temperatures for crop production. The amount of energy required will
vary with location, type of greenhouse, energy conservation measures,
and crop. In the Tennessee Valley area, the energy required for green-
house crop production may exceed 13.1 Tj/hectare (12,4 billion Btu/hectare)
or 5.3 Tj/,4 hectare (5 billion Btu/acre) and in Minnesota 19,3 Tj/hectare
(18.3 billion Btu/hectare) or 7.8 TJ/.4 hectare (7.4 billion Btu/
acre) (4). The U. S. Department of Agriculture reported in 1974 that
*1 quad = 1015
\
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108,914,015 m2 (357,329,446 ft2) or 3>320 hectares (8,203 acres) were used
for greenhouse space (5). By conservative estimates, the greenhouse
industry has grown by 5 percent each year since 1974 with a current esti-
mate of 4,237 hectares (10,469 acres). The average energy requirement for
greenhouses in the U. S. can probably be estimated by using the average
Btu requirement for greenhouse production in Minnesota and the Tennessee
Valley area which is approximately 16.1 Tj/hectare (15.3 billion Btu/hectare)
or 6.5 Tj/,4 hectare (6.2 billion Btu/acre). Based on this assumption, the
greenhouse industry uses in excess of 66 quadrillion joules (64 trillion Btu)
annually. The fuel equivalent of this amount of energy could be beneficially
used in the U. S. alone by utilizing waste heat. In addition, should most
of the greenhouses throughout the world eventually change to waste heat,
the energy saving will be even more substantial on a global scale.
Currently, 30 to 40 percent of the cost of greenhouse crop production
is used for energy and is increasing, while natural gas and fuel oil sup-
plies are becoming less available for greenhouse heating. Since most green-
houses are heated with natural gas, the present cost for 67 quadrillion
joules (64 trillion Btu) at $3.04/Gj ($3.20/million Btu) for natural gas
exceeds $204 million annually. The cost of 67 quadrillion joules (64
trillion Btu) supplied by No. 2 fuel oil at $6.45/Gj ($6.80/mi11ion Btu)
would exceed $433 million. Using waste heat at $.96/Gj ($1.02/million Btu),
the cost of 67 quadrillion joules (64 trillion Btu) would be $61.4 million.
In addition to conserving fossil fuels, the cost for energy could be
reduced by 232 percent or $142.6 million over the use of natural gas and
$371 million or 605 percent over the use of No. 2 fuel oil if waste heat
was used, while at the same time environmental pollution would be reduced
through the reduced combustion of fuel.
OBJECTIVES
This study investigated the potential beneficial use of industrial
waste heat for greenhouse production of bedding plants, cut flowers,
and foliage plants. The research facilities consisted of a conventional
greenhouse and a greenhouse modified to use simulated waste heat.
The major overall objectives of this research were: (1) to test
a feasible way to utilize waste heat, thereby conserving energy, (2) to
test the suitability of the greenhouse environment for the production
of ornamental and vegetable bedding crops, cut flowers and foliage
plants, and (3) to evaluate the overall economics of the system. The
more specific and detailed objectives are listed below:
Horticultural Objectives
1. To compare the quantitative growth data between the crops
grown in the control greenhouse and the crops grown in
the simulated waste heat greenhouse on the production of
bedding plants, foliage plants and cut flowers.
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2. To evaluate the incidence of diseases between the crops
grown in the control greenhouse and crops grown in the
simulated waste heat research greenhouse under high
relative humidity (90-100%) conditions.
Economic Objectives
1. To compare the annual cost of production for each crop
produced in the conventional greenhouse and the simulated
waste heat greenhouse.
2. To evaluate the economic implications of two production
management systems in both greenhouses,
3. To conduct limited market tests to determine consumer
acceptance of waste heat greenhouse production.
Engineering Objectives
1. To compare controlled-environment data of the control
greenhouse with that of the simulated waste heat green-
house for the entire year with reference to heating,
cooling and dehumidification.
2. To determine the responses of the control greenhouse with
that of the simulated waste heat greenhouse resulting
from changes initiated by a relatively sophisticated con-
trol system as well as changes from external pertubations,
A DESCRIPTION OF THE RESEARCH FACILITIES
The research facilities consisted of two quonset-type plastic
greenhouses, each 9.1 m X 21.9 m (30 ft X 72 ft). The plastic covering
for each greenhouse consisted of a double layer of Monsanto 602-6 mil
polyethylene plastic. One greenhouse served as a control and the other
greenhouse served as the waste heat research greenhouse,
The control greenhouse was not modified in any manner. It has a
climate control system equipped with fans, shutters, plastic convection
tube, two natural gas heating units, and controls to provide a suitable
greenhouse environment.
In £he control greenhouse, cooling is provided by an evaporative
Kool-cel pad located at one end of the greenhouse and two exhaust
fans located at the opposite end of the greenhouse. Heat is supplied
by two natural gas heaters with a heating capacity of 111 Mj (105,000
Btu) per hour. The heat is disseminated by a fan through a 0,61 m
(24 in) polyethylene convection tube with punched holes to bring about
even distribution of heat throughout the greenhouse,
*Trade Mark, ACME Engineering and Manufacturing Corporation
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The waste heat research greenhouse, on the other hand, is modified.
Both heating and cooling are supplied by evaporation from a 4.3 m X 2.7 m
(14 ft X 9 ft) Kool-cel pad through which air is circulated by two large
exhaust fans. For cooling, air is drawn through the Kool-cel pad and
discharged directly outside. Exactly 0.61 m (2 ft) of the Kool-cel pad is
located in the attic plenum. Intake louvers are located at one end of the
attic plenum. Since much of the heat from warm water is dissipated in the
top 0.61 m (2 ft) of the Kool-cel pad, much of the heat is discharged out
of the attic before it reaches the growing area of the greenhouse. This
modification in the design of the waste heat research greenhouse permits
the use of warm water during the summer months when the temperature of
industrial waste water, especially from power plants, is at its highest;
and yet, it will provide excellent evaporative cooling in the growing area
of the greenhouse;
Heating in the waste heat research greenhouse is provided by recircu-
lating air through the attic plenum over the Kool-cel pad and/or the fin-
tube system.
Simulation of waste heat for the waste heat research greenhouse is
supplied by a 105 KW electric water heater (boiler). The simulated
temperatures of water were based on the average monthly temperatures of
effluent condenser cooling water of each month of the year as obtained
from the Tennessee Valley Authority's Browns Ferry Nuclear Power Plant
located in Northern Alabama.
Located 1.2 m (4 ft) downstream from the Kool-cel pad is the fin-
tube system. The fin-tube system consists of two staggered rows of
0.05 m (2 in) radiation tubes 5.49 m (18 ft) lonq. The fins on the tubes are
0.1 m X 0.1 m (4 in X 4 in). Warm water is pumped through this system
of fin-tubes to provide a dry heat exchange and to aid in dehumidification.
The floor in each greenhouse consists of a concrete walkway 1.2 m
(4 ft) wide located in the center of the house with the remaining part
of the floor being covered with 0.1 m (4 in) of gravel.
Figure 1 and Figure 2 are schematic representations of the waste heat
research greenhouse and control greenhouse, respectively.
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ATTIC VENT FAN
RECIRCULATION
SHUTTERS^
-IlllJIIh
HI-
HEATING
COOLING
EXHAUST
SHUTTERS
POLYETHYLENE CEILING
—AIR FLOW
(FAN)
GROWING AREA
WATER
HEATER
FIN-TUBE -\
EXCHANGER \
Figure 1. A schematic representation of the waste heat research greenhouse.
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Hh
HEATERS
CONVECTION TUBE
O O O O O O
o o o
EXHAUST SHUTTERS
AIR FLOW
(FAN)
CONVECTION-TUBE FAN
KOOL-CEL PAD
GROWING AREA
SUMP
Figure 2. A schematic representation of the conventional greenhouse.
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SECTION 2
CONCLUSIONS
HORTICULTURAL
Cultivars of the following bedding plant species were transplanted
in late January and in early February of 1979 in the conventional green-
house and in the waste heat greenhouse: begonia, browallia, coleus,
geranuim, impatiens, marigold, pansy, petunia, salvia, tomato, and
verbena.
The data included in this report suggest that the growth rate of
the bedding plant species grown in this study are not adversely affected
by the waste heat greenhouse environment.
With the exception of browallia and coleus, the survival rate for
all other species of bedding plants grown in the waste heat research
greenhouse was comparable to the survival rate of those species grown
in the conventional greenhouse.
It was found that the plants grown in the conventional greenhouse
flowered approximately 7,6 days earlier than those grown in the waste
heat research greenhouse. However, this may be insignificant when
considering the amount of money saved in fuel cost,
The following species of foliage plants were transplanted in each
greenhouse from June 12, 1979, through July 14, 1979: Ardisia humilis,
Asparagus meyerii, Begonia Caribbean mix, Djzyotheca elegantissima,
Hypoestes sanguinolenta, Philodendron pertussum, Schefflera compacta,
and Syngonum podophyllum.
All of the above species grown in the waste heat research greenhouse,
with the exception of Ardisia humilis, showed a better growth rate than
those grown in the conventional greenhouse. The growth of Syngonium
podophyllum (nephthytis green) and Philodendron pertussum was statistic-
ally significantly better in the waste heat research greenhouse than in
the conventional greenhouse.
The waste heat research greenhouse environment seems to be highly
suited for growing foliage plants. This is probably brought about by
the higher percent relative humidity in the waste heat research green-
house than in the conventional greenhouse. Most foliage plants grow
better under a high percent relative humidity.
In regards to survival rate, there were no statistically signifi-
cant differences in survival rate between any of the species grown in
the conventional greenhouse and the waste heat research greenhouse. No
diseases were found in either greenhouse.
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ECONOMIC
Because data were analyzed from only one crop of bedding plants
and one crop of foliage plants, the economic conclusions made herein
are of a preliminary nature.
This study revealed that the waste heat greenhouse equipped with
a backup heating system would initially cost $84,506 to $90,605/.4
hectare (1 acre) or $208,730 to $233,794/hectare more to construct than
the same size conventional greenhouse.
If waste heat can be supplied for $0.96/Gj ($1.02/MBtu) as compared
to $3.04/Gj ($3.20/MBtu) and $6.45/Gj ($6.80/MBtu) for natural gas and
No. 2 fuel oil, respectively, it may result in a savings of $13,520/.4
hectare (1 acre) or $33,394/hectare when compared to natural gas and
$35,685/.4 hectare (1 acre) or $88,142/hectare when compared to No. 2
fuel oil.
Considering the current increasing price rates for natural gas
and No. 2 fuel oil, the number of years required to break even for the
cost of using waste heat to heat a greenhouse can probably be reduced
to 3 to 4 years relative to heating with natural gas and 1 to 2 years
for heating with No. 2 fuel oil by 1985.
With reference to marketing and consumer acceptance, customers
did not show any preference in buying plants grown in the conventional
greenhouse over those grown in the waste heat research greenhouse.
The quality of plants grown in the waste heat research greenhouse was
equal to the quality of those grown in the conventional greenhouse.
ENGINEERING
The engineering performance of the waste heat research greenhouse
was compared with the conventional greenhouse in regards to heating,
cooling and relative humidity.
In regards to maintaining heat, the waste heat research greenhouse
was able to maintain an average low nighttime temperature of 12.0°C
(53.6°F) over a 24-day period during the month of February while using
water heated to 21.8°C (71.2°F) with a flow rate of 109 liters/minute
(24 gallons/minute). The average low outside temperature for the same
period was 2.6°C (36.7°F). Bedding plants grown in the waste heat
research greenhouse did not suffer any adverse effects when compared to
those grown in the conventional greenhouse. The waste heat research
greenhouse is quite capable of providing a suitable winter-time tempera-
ture for the species of bedding plants tested in this project.
With reference to cooling, over a 4-day period the waste heat
research greenhouse in July was able to maintain an average high day-
time temperature of 30.0°C (86.0°F) in comparison to 29.4°C (85°F)
maintained by the conventional greenhouse. The temperature of the
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entering effluent water used to cool the waste heat research greenhouse
during this period was 43. PC (109.6°F). The average outside temper-
ature for the same four-day period was 38.6°C (101.5°F). These data
indicate that warm effluent water can be used effectively to cool
greenhouses, provided that much of the heat associated with the effluent
water can be dissipated from the greenhouse through an attic before
reaching the growing area.
For the most part, the relative humidity averaged only a few percent
higher in the waste heat research greenhouse than it did in the conventional
greenhouse. At no time was there condensation of water vapor observed on
the foliage of plants grown in the waste heat research greenhouse or the
conventional greenhouse.
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SECTION 3
RECOMMENDATIONS
It is recommended that:
(1) The industry associated with the production of thermal water
(waste heat) and the greenhouse industry apply the findings
of this project to help eliminate thermal pollution of our
waterways while benefitting both industries.
(2) A longer study period (4 to 5 years) be given to the evaluation
of the crops observed in this study to help verify the results
stated herein.
(3) A longer study period (4 to 5 years) be given to further
evaluate the greenhouse design and control of the greenhouse
environment.
(4) Additional research be given to finding those species of
bedding plants and foliage plants that are best suited to
the environment of a waste heat greenhouse.
(5) The growth response of woody ornamentals be tested with waste
heat.
(6) More research be given to the economic evaluation in comparing
waste heat greenhouse crop production with that of conventional
greenhouse crop production.
10
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SECTION 4
HORTICULTURAL STUDIES
Horticultural studies began in January, 1979. All horticultural
studies followed the time table listed below:
1. January through April of 1979, cultivars of the 10
leading ornamental bedding plant crops along with the
2 leading vegetable bedding plant crops were grown in
each greenhouse.
2. May through September of 1979, cultivars of the leading
species of foliage plants and plants adapted for hanging
baskets were grown in each greenhouse.
The greenhouses were not completed in time to schedule a fall crop
(August through December of 1978). Therefore, this report contains data
collected on bedding plants grown in each greenhouse from January, 1979,
through April, 1979, and foliage plants grown June, 1979, through
September, 1979.
Both the conventional greenhouse and the waste heat research green-
house were operated as a commercial-type enterprise, and all parts of
the system were evaluated, both from the standpoint of mechanical opera-
tion and as a satisfactory structure for plant growth.
Bedding Plants
All bedding plants were grown from super seddings obtained from the
Ball Seed Company of Chicago, Illinois. Jiffy Mix Plus served as the
soil medium.
Seedlings for each species and cultivar were transplanted to cell
paks (32/tray), with the exception of geraniums which were transplanted
into O.lm (4 in) standard pots. After transplanting, trays and pots for
each species were equally divided, and half were placed into the conven-
tional greenhouse and the other half placed in the waste heat research
greenhouse.
Figure 3 depicts the arrangement of the bedding plant species in
both greenhouses. The statistical design used for the analysis of
variance was the randomized complete-block design (10). A 1.2m (4 ft)
space was placed between each block (replication).
Dry Weights (the whole plant). Table 1 depicts the mean dry weight
of the whole plant for all species, except peppers. (The pepper seedlings
were lost in both greenhouses due to mice). The growth rate of geraniums,
petunias, and verbenas in the conventional greenhouse was statistically
greater as compared with the same species grown in the waste heat research
greenhouse. Although begonias, browallias, coleus, impatiens, marigolds,
11
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Figure 3. The arrangement of bedding plant species in the waste heat research greenhouse.
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pansies, salvias and tomatoes grown in the conventional greenhouse
showed a slightly better growth than those grown in the waste heat
research greenhouse, the differences in growth rates were not statis-
tically significant.
TABLE 1. MEAN DRY WEIGHT (g) of 8 WHOLE PLANTS/REPLICATION,
APRIL 1, 1979Z
SPECIES
Begonia
Browallia
Coleus
Geranium
Impatiens
Marigold
Pansy
Petunia
Sal via
Tomato
Verbena
DAYS FROM
TRANSPLANTING
50
48
49
47
49
50
40
49
48
40
40
CONVENTIONAL
GREENHOUSE
WASTE HEAT
RESEARCH GREENHOUSE
11.
8.
7.
17,
12.
14.
11.
17.
13.
17.
25a
OOa
87a
25a
87a
90a
50a
50a
OOa
50a
10.
6.
6.
13.
11.
14.
10.
14.
12.
15.
87a
37a
25a
25b
37a
OOa
25a
87b
25a
30a
13.70a
10.37b
zMeans sharing uncommon letters are significant at the 5% level.
Table 2 shows the dates plants were treated with a 0.5% solution
of B-nine, a growth retardant. The different species of bedding plants
were sprayed with the growth retardant when they showed signs of stretch-
ing. B-nine was applied with a 7.57 1 (2 gal) sprayer. Some difficulty
was experienced with obtaining a uniform flow from the sprayer. This
nonuniform application of B-nine probably resulted in some variation in
growth rate noted among species grown in the same greenhouse as well as
differences noted among species grown in separate greenhouses.
TABLE 2. SPRAY DATES OF B-NINE GROWTH RETARDANT
SPECIES
Browallia
Coleus
Geranium
Impatiens
Pansy
Petunia
Salvia
Verbena
SPRAY DATES
3-27-79
3-13-79 & 4-16-79
3-17-79, 3-27-79 & 4-16-79
3-12-79 & 3-27-79
3-13-79
3-12-79
3-12-79
3-12-79 & 3-27-79
Dry Weight (aerial plant parts). Table 3 shows the mean dry weight
of the aerial parts of each species. Coleus and tomato plants grown in
the conventional greenhouse showed a statistically significant better
growth rate than those grown in the waste heat research greenhouse.
13
-------
Petunias grown in the waste heat research greenhouse showed a growth
rate significantly better than those grown in the conventional green-
house, but better growth was probably due to a heavier application of
B-nine in the conventional greenhouse.
TABLE 3. MEAN DRY WEIGHT (g) OF 20 AERIAL PLANT PARTS/REPLICATION,
APRIL 12, 19792
SPECIES
Begonia
Browallia
Coleus
Geranium
Impatiens
Marigold
Pansy
Petunia
Sal via
Tomato
Verbena
DAYS FROM
TRANSPLANTING
61
59
60
58
60
61
51
60
59
51
51
CONVENTIONAL
GREENHOUSE
19.75a
12.90
9.63a
40.87a
Sl.OOa
24.50a
22.12a
25.50a
22.37a
45.00a
23.50a
WASTE HEAT
RESEARCH GREENHOUSE
19.37a
9.30a
6.63b
42.51a
29.00a
25.50a
22.12a
37.75b
20.12a
42.50b
23.50a
zMeans sharing uncommon letters are significant at the 5% level.
Geraniums and marigolds grown in the waste heat research greenhouse
showed a slightly better growth rate (but not statistically) than those
grown in the conventional greenhouse. The reverse was true for begonias,
browallias, impatiens and salvias. Pansies and verbenas showed equal
growth rates in both greenhouses.
Flowering Dates in Paks and Pots. Table 4 depicts and compares the
number of days required to flower in paks and pots for each species in
each greenhouse. The plants grown in the waste heat research greenhouse
flowered on the average of 7.6 days (approximately one week) later than
those grown in the conventional greenhouse. The greatest difference in
flowering was noted in the geraniums which flowered 9 days earlier in
the conventional greenhouse. Begonias, browallias, impatiens, and mari-
golds flowered 8 days earlier in the conventional greenhouse. Pansies,
petunias, salvias, and verbenas grown in the conventional greenhouse
flowered 7 days earlier than those grown in the waste heat research
greenhouse.
Tomatoes are not listed in Table 4 because tomato bedding plants
were sold according to plant size. Tomato plants had reached a saleable
size in both greenhouses at the end of 4 weeks.
14
-------
TABLE 4. FLOWERING DATES OF BEDDING PLANTS IN PAKS
SPECIES
CONVENTIONAL
GREENHOUSE
WASTE HEAT
RESEARCH GREENHOUSE
DAYS DIFFERENCE
IN BLOOMING
TIME FROM TIME FROM
TRANSPLANTING DATE OF TRANSPLANTING DATE OF
TO BLOOM (DAYS) BLOOM TO BLOOM DAYS) BLOOM
Begonia
Browallia
Geranium
Impatiens
Marigold
Pansy
Petunia
Sal via
Verbena
31
61
79
33
23
36
39
38
45
3-13-79
4-12-79
4-30-79
3-16-79
3-5-79
3-28-79
3-21-79
3-20-79
4-6-79
39
69
88
41
31
43
46
45
52
3-21-79
4-20-79
5-9-79
3-24-79
3-13-79
4-4-79
3-28-79
3-27-79
4-13-79
8
8
9
8
8
7
7
7
7
Survival Rate. Table 5 shows the survival rate for each species of
bedding plants in the conventional greenhouse and the waste heat research
greenhouse. Only two species, browallia and coleus, showed a statistically
significant better survival rate in the conventional greenhouse than in the
waste heat research greenhouse. Browallia had an 81.0% survival rate in
the conventional greenhouse and 66.0% in the waste heat research green-
house. Coleus had an 89.5% survival rate in the conventional greenhouse
compared to 78.0% in the waste heat research greenhouse. For all other
species, the survival rate was not statistically significantly different
between the two greenhouses.
TABLE 5. MEAN SURVIVAL RATE BASED ON 4 FLATS/REPLICATION (128 PLANTS)
APRIL 10, 1979Z
SPECIES
Begonia
Browallia
Coleus
Geranium
Impatiens
Marigold
Pansy
Petunia
Sal via
Tomato
Verbena
DAYS FROM
TRANSPLANTING
59
57
58
56
57
59
49
58
57
49
49
CONVENTIONAL
GREENHOUSE
95.5
81. Oa
89.5a
98.8a
100.Oa
98.7a
99.2a
100.Oa
96.2a
100.Oa
97.5a
WASTE HEAT
RESEARCH GREENHOUSE
91.7a
66.Ob
78.Ob
98.4a
100.Oa
96.7a
99.5a
100.Oa
97.5a
100.Oa
97.5a
zMeans sharing uncommon letters are significant at the 5% level
15
-------
Foliage Plants
Foliage plants were grown in both greenhouses from June 12, 1979
through September, 1979. Table 6 shows the species and cultivars that
were grown in both greenhouses.
TABLE 6. SPECIES AND CULTIVARS
SPECIES TRANSPLANTING DATE
Ardisia humilis 7_14_79
Asparagus meyerii 7-14-79
Begonia Caribbean mix 6_2i-7g
Dizyotheca elegantissima 6-21-79
Hypoestes sanguinolenta 7-5-79
Philodendron pertussum 7-5-79
Schefflera compacta 7-5-79
Syngonium podophyllum 6-21-79
Foliage plants were also obtained from Ball Seed Company as super
seedlings. All seedlings did not arrive on the same date, and trans-
planting took place from June 12, 1979, through July 14, 1979.
Dry weight (aerial plant parts). Dry weights were taken August 23,
1979, on Dizyotheca elegantissima (false aralia). Ardisia humilis,
Begonia Caribbean mix, Syngonium podophyllum (nephthytis green) and
Hypoestes sanguinolenta (polka dot plant).
For comparison, Table 7 depicts the mean dry weight for the five
species of foliage plants grown in both greenhouses. With the exception
of Ardisia humilis, the remaining species grew better in the waste heat
research greenhouse than they did in the conventional greenhouse. Syngo-
mum podophyllum (nephthytis green) grew significantly better in the
waste heat research greenhouse than it did in the conventional greenhouse.
TABLE 7. MEAN DRY WEIGHT (g) OF AERIAL PLANT PARTS, AUGUST 23, 1979Z
PLANTS/ DAYS FROM CONVENTIONAL WASTE HEAT
SPECIES REPLICATION TRANSPLANTING GREENHOUSE RESEARCH GREENHOUSE
Dizyotheca
elegantissima 10 63 6.38a 7 12a
Ardisia humilis 10 40 3.74a 3.66a
Begonia Carrifa-
bean mix 10 63 19.72a 21.43a
Syngonium
podophyllum 20 63 34.80a 43.70b
Hypoestes
sanguinolenta 20 63 100.20a 92.20a
zMeans sharing uncommon letters are significant at the 5% level.
16
-------
The mean dry weight for Asparagus meyerrL Philodendron pertussum
and Schefflera compacta were taken on September 19, 1979. Table 8 shows
that Philodendron pertussum grew significantly better in the waste heat
research greenhouse than in the conventional greenhouse. Although the
growth rates were not significantly better, both Asparagus meyerii and
Schefflera compacta grew better in the waste heat research greenhouse
than in the conventional greenhouse. These data indicate that foliage
plants responded well to the waste heat greenhouse environment.
TABLE 8. MEAN DRY WEIGHT (g) OF AERIAL PLANT PARTS, SEPTEMBER 19, 1979Z
PLANTS/ DAYS FROM CONVENTIONAL WASTE HEAT
SPECIES REPLICATION TRANSPLANTING GREENHOUSE RESEARCH GREENHOUSE
Asparagus
meyerii 10 67 5.31a 5.75a
Philodendron
Pertussum 5 76 19.32a 22.60b
Schefflera
compacta 5 76 12.45a 13.96a
zMeans sharing uncommon letters are significant at the 5% level.
Survival Rate. Table 9 shows the survival rate for each species
grown in both greenhouses. In regards to survival rate, the waste heat
research greenhouse provided a favorable environment equal to that of the
conventional greenhouse. As a result of using normal disease preventive
practices which were identical for each greenhouse, no evidence of any
diseased plants was found.
TABLE 9. MEAN SURVIVABILITY BASED ON 100 PLANTS/REPLICATION
AUGUST 23, 1979Z
DAYS FROM CONVENTIONAL WASTE HEAT
SPECIES TRANSPLANTING GREENHOUSE RESEARCH GREENHOUSE
Dizyotheca
elegantissima 63 100.Oa 100 Oa
Ardisia humilis 40 100.Oa 100 Oa
Asparagus meyexjj_ 40 100.Oa loo'oa
Caribbean mix
be9onia 63 97.3a 96.8a
Syngonium
podophyllum 63 100.Oa loo oa
Philodendron
pertussum 49 100.Oa 100 Oa
Hypoestes
sanguinolenta 49 100.Oa loo oa
Schefflera
comPacta 49 loo.Oa 100.Oa
zMeans sharing uncommon letters are significant at the 5% level.
17
-------
SECTION 5
GREENHOUSE PERFORMANCE
Histories for temperature and percent relative humidity were
compared for the conventional greenhouse and the waste heat research
greenhouse. Temperature was recorded by a Bendix hygro-thermograph,
and the percent relative humidity was measured with a hand psychro-
meter. Both temperature and the percent relative humidity readings
were taken on the floor in the center of each greenhouse and on the
outside of the greenhouses.
The flow rate of warm water was set at 109 1/min (24 gal/min)
in the waste heat research greenhouse; the same flow rate was used
for both winter and summer.
The temperature of power plant effluent water will vary according
to whether the power plant is operating on a closed cycle or an open
cycle and also according to each month of the year. Table 10 shows
the temperature of effluent water for both a closed cycle and an open
cycle power plant at the TVA's Browns Ferry nuclear power plant located
in north Alabama. As shown in Table 10, the temperature of effluent
water will be higher from a power plant operating on a closed cycle
than from a power plant operating on an open cycle.
TABLE 10.
MONTH
January
February
March
April
May
June
July
August
September
October
November
December
AVERAGE MONTHLY TEMPERATURE OF EFFLUENT WATER AT BROWN'S
FERRY NUCLEAR POWER PLANT LOCATED IN NORTH ALABAMA9
CLOSED CYCLE
TEMPERATURE
OPEN CYCLE
TEMPERATURE
C
21.30
21.80
24.40
31.30
35.80
40.60
43.10
43.20
40.60
35.70
29.10
24.40
F
70.34
71.24
75.92
88.34
96.44
105.08
109.58
109.76
105.08
96.26
84.38
75.92
C
43.10
43.90
45.10
47.20
49.00
50.50
51.20
51 . 20
49.90
47.70
45.40
F
109.58
111.00
113.18
116.96
120.20
122.90
124.16
124.16
121.82
117.86
113.72
43.20
109.76
aEarl Burns. Personal Communication. TVA. October, 1978.
In this study, the temperature of water used in the waste heat research
greenhouse simulated the temperature of effluent water coming from an open
cycle power plant throughout the year, with the exception for short periods
when the temperature of effluent water coming from a closed cycle plant was
simulated for testing purposes only.
1!
-------
HEATING
During February, 1979, the temperature of effluent water from
open cycle operation was 21.8°C (71.2°F) as shown in Table 10. The
water used in the waste heat research greenhouse was heated to this
temperature. Each greenhouse had the nighttime temperature set at
15.5°C (60°F) and a daytime temperature setting at 21.1°C (70°F).
During a 24-day period in February, the waste heat research
greenhouse maintained an average low night temperature of 12.0°C
(53.6°F). The conventional greenhouse average low night temperature
was 14.1UC (57.4°F). This was a difference of 2.1°C (3.8°F). The
average low outside night temperature for this period was 2.6°C
(36.7°F) as depicted by Figure 4.
It is important to note here that the temperature control box in
each greenhouse was located approximately 1.2 m (4 ft) above floor level.
However, the hygro-thermographs recorded the temperatures at floor
level where bedding plants are commonly grown in greenhouses. Temper-
ature stratification is common in greenhouses and is the major reason
for the difference between the greenhouse set temperature and the
temperatures recorded at floor level.
Figure 5 depicts the average high daytime temperature maintained
in the waste heat research greenhouse and the conventional greenhouse
along with the average high outside temperature for the same 24-day
period in February. The waste heat research greenhouse maintained an
average high temperature of 18.4°C (65.1°F), whereas the conventional
greenhouse maintained an average high temperature of 21.6°C (70.9°F).
The average high outside temperature for the period was 12.6°C (54.7°F).
One of the coldest days of the year was February 18, 1979. On
that date, there was an ice-snow storm. Wind speed reached above
17.9 m/s (40 mph) and the outside temperature reached a low of -4.4°C
(24°F) (Figure 6). The lowest temperature reached in the waste heat
research greenhouse was 8.9°C (48°F). This was less than 2°C difference
in the lowest temperature recorded in the conventional greenhouse which
was 10.6°C (51°F).
Figure 7 shows the 24-hour per day temperature histories for both
greenhouses over a 4-day period in January.
The waste heat research greenhouse fin-tube heat exchanger system
was designed to provide adequate dry heat. The fin-tube heat exchanger
system consisted of 18 fin tubes, 0,05 m (2 in) diameter by 5.49 m (18 ft)
length, 0.05 m (2 in) square plate fins, with 2 fins/0.03 m (1 in). However
the 1/3 hp pump provided only enough water to fill the bottom 4 fin tubes
with warm water. Therefore, the heat in the waste research greenhouse was
obtained by pumping water over the pad.
19
-------
IN3
o
30
n>
-o
05
-5
DJ
n>
o
o
10
86
68
WASTE HEAT
GREENHOUSE
14.1.
-(53.6°F)
CONVENTIONAL
GREENHOUSE
-(57.4°F)
50
n>
-a
n>
-5
DJ
t-t-
C
-s
ro
2.6_OUISIDL___(36.70F)
32
Figure 4. Average low night air temperature from February 1 through February 24, 1979.
-------
40 -
30
-s
QJ
20
10
•104
86
18.4-
WASTE HEAT
GREENHOUSE
CONVENTIONAL
21-6_ GREENHOUSE
68
-s
QJ
H-
c:
-s
1? fi. OUTSIDE
J54.7°F)
50
Figure 5. Average high daytime air temperature from February 1 through February 24, 1979.
-------
30
20
ro
ro
T3
ro
-s
ro
o
o
10
8.9-
-4.4*
-10
OUTSIDE (24.QQF)
WASTE HEAT
GREENHOUSE
10.6-
-(48.QOF)
CONVENTIONAL
GREENHOUSE
86
68
50
0)
-a
ro
-s
a>
,t-i-
c:
ro
32
14
Figure 6. Comparative air temperature history of 24-hour period in the waste heat research greenhouse
during an ice-snow storm on February 18, 1979.
-------
IX)
OJ
ro
3
TD
ro
G)
rp
o
o
CONVENTIONAL GREENHOUSE
WASTE HEAT GREENHOUSE
OUTSIDE
0 4 8 12 16 20 24 4
January 21
8 12 16 20 24 48 12 16 20 24 48 12 16 20
January 22 January 23 January 24
n
-d
-5
QJ
Figure 7. Comparative air temperature histories over a four-day period in January, 1979,
-------
COOLING
Both greenhouses were covered with an 80 percent K-shade cloth
to provide favorable light conditions for foliage plants and to aid
in cooling. Figure 8 shows the average high temperature for both
greenhouses during a hot 4-day period in July using warm water heated
to 43.1°C (109.6°F) to cool the waste heat research greenhouse. During
this 4-day period, the average high temperature in the waste heat
research greenhouse was 30°C (86°F) and 29.4°C (85°F) in the conven-
tional greenhouse. The average high outside temperature covering the
same period was 38.6°C (101.5°F). Figure 9 shows cooling for 24 hours
per day during the same 4-day period in July.
As mentioned previously, the temperature of effluent water
coming from a closed cycle power plant is higher than the temperature
of effluent water coming from an open cycle power plant. To test
the effectiveness of cooling a greenhouse with the higher temperature
effluent water coming from a closed cycle power plant and under high
relative humidity conditions, the hot water heater was set at 51.2°C
(124.2°F) for several days during July and August.
Figure 10 shows the temperatures maintained by each greenhouse
and the outside temperature for a 4-day period during August while
using the higher temperature water in the waste heat research green-
house. The average high temperature reached in the waste heat research
greenhouse during this 4-day period was 27.2°C (81°F) and 25.4°C
(77.8°F) in the control greenhouse. This represented only a difference
of 1.8°C (3.2°F) between the control greenhouse and the waste heat
research greenhouse. The average high temperature reached outside of
the greenhouses was 34.6°C (94.3°F) for the same 4-day period.
It is important to note that evaporative cooling is limited by
the attainment of 100% relative humidity in a greenhouse and the rela-
tive humidity of the outside air supplied to the evaporative cooler.
As mentioned in the next section, the relative humidity in the waste
heat research greenhouse was generally higher than the relative humidity
in the conventional greenhouse. However, the noted differences in
relative humidity between the two greenhouses were generally small.
Therefore, if the relative humidity can be controlled, the data repre-
sented by Figure 10 indicate that the higher temperature effluent water
from a closed cycle power plant can be used effectively to cool green-
houses during the hot summer months.
An effort was made to determine the rate of sensible heat exchange
from effluent water to air. The temperature of effluent water (from
the hot water heater), the temperature of the effluent water 0.61 m
(2 ft) below the top of the evaporative pad (attic level), and the
temperature of the effluent water at the base of the evaporative pad
2.7m (9 ft) below the top of the evaporative pad, were taken. The
average temperature of effluent water for each of the above points
24
-------
0)
3
T3
rt>
-5
Q)
(-+
c:
-~>
o>
40
30
20
10
38.6-
OUTSIDE
WASTE HEAT
?n n GREENHOUSE
-(86.0°F)
29.4
CONVENTIONAL
GREENHOUSE (g5.nQF)
•(101.5°F)
104
86
68
50
32
rp
-5
-5
o>
Figure 8. Average high greenhouse temperatures with water heated to 43.1°C (109.6°F) in the waste
heat research greenhouse from July 1 through July 4, 1979.
-------
en
CO
T3
CO
-s
01
-s
CO
o
:o
50
40
30
20-
OUTSIDE
WASTE HEAT GREENHOUSE
CONVENTIONAL GREENHOUSE
10
122
104
86
68
MM 50
4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24 4 8 12 16 20 24
CO
-a
a>
-s
QJ
cf
C
ro
Figure 9. Comparative cooling during 24-hour cycles between waste heat greenhouse and
conventional greenhouse using water heated to 43.1°C (109.6°F).
-------
40
104
34.6_
OUTSIDE
30
[ND
ro
3
-a
ro
-s
CU
. o
-o
WASTE HEAT
97 9 GREENHOUSE («l.nQF)
20
10
CONVENTIONAL
GREEMHOUSF
(Q/I
86
68
rt>
T3
rt>
-s
CD
c-t-
ro
50
32
Figure 10. Average high temperatures reached in greenhouses using water heated to 51.2°C (124.6°F)
the waste heat research greenhouse simulating the temperature of effluent water from a
closed cycle plant (August 14-17, 1979).
-------
over a 6-day period (August 29, through September 3, 1979) is depicted
in Figure 11. There is a total average drop in temperature of 27.5°C
(49.50F) from the temperature of the effluent water to the base of the
evaporative pad and a 21.1°C (38.0°F) drop in temperature from the tem-
perature of the effluent water just 0.61 m (2 ft) below the top of the
evaporative pad. This indicated that 77 percent of the total amount of
heat dissipated from effluent water by evaporative cooling occurred in
the top 0.61 m (2 ft) of the evaporative pad. Since the top 0.61 m (2 ft)
of the evaporative pad was above the attic level, it meant that over
three-fourths of the heat from the warm effluent water was exhausted out
of the attic plenum and never entered the growing area of the greenhouse.
This also meant that the attic plenum was effective in dissipating the
excess heat associated with effluent water from the growing area of the
greenhouse during the warm months of the year. Furthermore, it permitted
the use of a greater volume of warm effluent water during the warm months
of the year without adversely affecting greenhouse crop production. The
greater the volume of warm water used by a greenhouse operator during
the summer months, the more beneficial it is to the power plant.
RELATIVE HUMIDITY
Due to the large cost over-run on the construction of the two
greenhouses, funds were not available to purchase three recording
hygrometers. A hand psychrometer was purchased during the spring of
1979. Therefore, data concerning the relative humidity were taken
during the spring and summer months only.
All psychrometric readings were taken at floor level in the
center of each greenhouse. Table 11 shows the relative humidity for
each greenhouse and the outside for a 10-day period during the month
of August under various environmental conditions and at different times
during the 24-hour day. Table 11 shows that the relative humidity was
generally higher in the waste heat research greenhouse than it was in
the conventional greenhouse. However, in some instances there was
either no difference or only small differences between the relative
humidity in the waste heat research greenhouse and conventional green-
house at the time the psychrometric readings were taken. At no time
was there any observed condensation of water vapor on foliage of plants
grown in either greenhouse. The high relative humidity did not pose a
problem in either greenhouse.
It is important to note that each psychrometric reading in Table
11 took approximately 3 minutes. The psychrometric readings were made
by using a slide rule humidity calculator. Although extreme care was
used in taking the relative humidity readings from the slide rule
humidity calculator, there is a possibility that some errors could
have been made. This is probably exemplified by the 12:00 a.m. and
3:00 p.m. relative humidity readings taken on 8-23-79 for both green-
houses as well as for the relative humidity readings taken on 8-25-79
and 8-26-79 for the waste heat research greenhouse as depicted in
Table 11. The relative humidity of the outside air and the prevailing
28 :
-------
53.7-
TEMPERATURE OF
EFFLUENT WATER
50
40 —
fD
-a
fD
a>
03
O
o
30
20
10
•(128.7°F)
TEMPERATURE OF
EFFLUENT WATER
AT ATTIC LEVEL
32.6
(90.7°F)
TEMPERATURE OF
EFFLUENT WATER
AT BASE OF PAD
OUTSIDE
28.6 TEMPERATURE
26.2
(79.1°F)
22
04
86
-a
ro
-s
fD
68
50
Figure 11. Potential for sensible heat exchange from effluent water to air during evaporative cooling
in the waste heat research greenhouse from August 29 through September 3, 1979.
-------
TABLE 11.
PERCENT RELATIVE HUMIDITY WITH EFFLUENT WATER TEMPERATURE
SET AT 51.7°C (125.0°F)
DATE
TIME
8-15-79
8-17-79
8-17-79
8-18-79
8-19-79
8-20-79
8-21-79
8-22-79
8-23-79
8-23-79
8-23-79
8-25-79
'8-26-79
8-26-79
5:00 p.m
12:40 p.m
6:10 p.m
2:00 p.m
2:00 p.m
1:20 p.m
12:00 a.m
12:00 a.m
12:00 a.m
3:30 p.m
11 :30 p.m
12:30 p.m
1:00 p.m
8:00 p.m
WASTE HEAT
RESEARCH
GREENHOUSE
80
83
92
70
68
80
92
96
96
96
100
80
82
96
CONVENTIONAL
GREENHOUSE
80
82
87
70
65
80
92
92
98
92
100
72
70
96
OUTSIDE
OUTSIDE CONDITIONS
62 cloudy
68 cloudy
68 cloudy
52 partly cloudy
46 clear-sunny
56 partly cloudy
80 midnight
78 midnight
100 midnight-raining
100 raining
100 night-raining
78 partly cloudy
72 partly cloudy
84 cloudy
environmental conditions at the time the relative humidity readings
were taken on the previously mentioned dates do not support the rela-
tive humidity readings found in the greenhouses and are probably
erroneous.
The relative humidity in a greenhouse can quickly change as
the external environmental conditions change (such as sunlight, cloud
cover or rain). A better evaluation could have been given on the
comparison between the relative humidity in the waste heat research
greenhouse and the conventional greenhouse with a 24-hour per day
recording hygrometer.
Although psychrometric determinations were not made during the
winter months due to the lack of a psychrometer, visual observations
were noted. When fogging was observed in the waste heat research
greenhouse in the winter, it always occurred at night or during the
daytime when the cloud cover was heavy. The fog always formed about
4 feet above the floor level and upward to the attic. The foliage
of bedding plants, which were grown on the floor of each greenhouse,
never showed any signs of condensation of water vapor.
Fog formation in the winter months can be eliminated from a
waste heat greenhouse by the use of dry heat exchangers such as a
fin-tube system. As noted earlier, the pump installed to circulate
water through the 18 radiation fin-tubes has only sufficient capacity
to circulate water through the bottom 4 of these tubes. Therefore,
only 22 percent of the radiation fin-tube system was providing heat
or participating in the heating and drying process.
30
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SECTION 6
ECONOMIC APPROACH AND MARKETING STUDIES
ECONOMIC APPROACH
Because data were analyzed from only one crop of bedding plants
and one crop of foliage plants, the economic projections made herein
are of a preliminary nature.
The economic approach in this study is based on a comparison
between a year-round commercial waste heat greenhouse operation with
that of a conventional greenhouse operation. The projected savings
in fossil fuel and cost of greenhouse production are on a .4 hectare
(1 acre) basis.
The economics discussed in this study are based on one crop of
bedding plants (winter and spring of 1979), one crop of foliage plants
(spring and summer of 1979), and a projected crop of potted chrysan-
themums and poinsettias (summer and fall of 1979). A costrreturn for
each type of greenhouse operation is based on 0.093 m2 (ft2) of space
used per flat base and per pot base for certain crops grown in this
study with reference to an annual savings in fossil fuel and the cost
of fossil energy for the greenhouse production of these crops.
The economic data in this study are based on the following: (1)
the difference in construction cost of a .4 hectare (1 acre) waste
heat greenhouse compared to a .4 hectare (1 acre) conventional green-
house, (2) the cost of a back-up heating system for a .4 hectare (1
acre) waste heat greenhouse, (3) the average annual energy (Gj) require-
ment needed to heat a .4 hectare (1 acre) greenhouse in the U. S., (4)
the current cost/Gj for natural gas and No. 2 fuel oil, (5) the projected
cost for the waste heat, and (6) the wholesale value of certain crops
grown in this study.
CONSTRUCTION COST
Basic Cost. The cost of construction materials used to build the
9.1 m X 21.9 m (30 ft X 72 ft or 2,160 ft2) conventional greenhouse
was $5,264 or $26.24/m2 ($2.44/ft2). This cost is equivalent to
$106,157/.4 hectare (1 acre) or $262,207/hectare. The cost of erecting
the 201 m2 (2,160 ft2) conventional greenhouse was $7.96/m2 ($0.74/ft2)
or $1,600 which is equivalent to $32,267/.4 hectare (1 acre) or $79,6987
hectare. The combined total cost of construction materials and the
erection of the 201 m2 (2,160 ft2) conventional greenhouse was $6,863
or$34.19/m2($3.18/ft2). This cost is equivalent to $138,404/.4 hectare
(1 acre) or $341,858/hectare.
The cost of construction materials for the 9.1 m X 21.9 m (30 ft X
72 ft or 2,160 ft2) waste heat research greenhouse was $8,098 or
31
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$40.32/m2 ($3.75/ft2). This cost is equivalent to $163,3107.4 hectare
(1 acre) or $403,375/hectare. The cost of erecting the 201 m2 (2,160
ft2) waste heat research greenhouse was $2,532 or $12.58/m2 ($1.17/ft2)
which is equivalent to $51,062/.4 hectare (1 acre) or $126,123/hectare.
The combined total cost of construction materials and erection of the
201 m2 (2,160 ft^) waste heat research greenhouse was $10,630 or
$52.90/m2 ($4.92/ft2). This cost is equivalent to $214,372/.4 hectare
(1 acre) or $529,499/hectare.
The average cost of construction materials for the conventional
greenhouse was $26.24/m2 ($2.44/ft2) compared to $40.32/m2 ($3.75/ft)
for the construction materials of the waste heat research greenhouse.
This represents $57,1537.4 hectare (1 acre) or $141,168/hectare or
54 percent more for the cost of construction materials for the waste
heat research greenhouse compared to the conventional greenhouse. This
added cost for a waste heat greenhouse is primarily due to the added
fin-tube heater system, attic fans, attic intake louvers, and attic
exhaust shutters.
The erection cost for the conventional greenhouse was less than the
erection cost for the waste heat research greenhouse by about 58 percent.
The erection cost of the 201 m2 (2,160 ft2) conventional greenhouse was
$7.96/m2 ($0.74/ft2) compared to $12.58/m2 ($1.17/ft2) for the same size
waste heat research greenhouse. This represents an increase of $18,7957
.4 hectare (1 acre) or $46,425/hectare or 58 percent more for the erection
cost of a waste heat greenhouse compared to that of a conventional green-
house. Like the difference in cost of construction materials, the added
difference in the erection cost of a waste heat greenhouse is primarily
due to installing the fin-tube heating system, the attic intake louvers,
the attic exhaust fans, and attic exhaust shutters.
Although the waste heat research greenhouse used in this study did
not have a back-up heating system, according to the analysis of data, it
cost $34.19 m2 ($3.18/ft2) to construct a conventional greenhouse as
compared to $52.90/m2 ($4.92/ft2) for a waste heat greenhouse; this
means that the basic waste heat greenhouse will cost approximately 55
percent more to construct than a conventional greenhouse. Thus, the
basic waste heat greenhouse will cost $187,641/hectare or $75,968/.4
hectare (1 acre) more to construct than will the conventional greenhouse
(Table 12).
Back-Up Heating System. Since the waste heat research greenhouse
used in this study does not have a back-up heating system, such a heat-
ing system was not used in computing the previous cost. However, a
commercial waste heat greenhouse operator would need a back-up heating
system in the event the power plant could not deliver warm effluent
water to the greenhouse. The cost of a back-up heating system having
the equivalent capacity of 4.5 Gj/hr/.4 hectare (4.3 MBtu/hr/acre) will
cost approximately $15,000 for oil and $8,500 for natural gas (Table 13).
This represents an additional $3.66/m2 ($0.34/ft2) for the oil-fired
back-up heating system or $2.15/m2 ($0.20/ft2) for a gas-fired back-up
system. This additional cost should be added to the previous $52.90/m2
32
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TABLE 12. COMPARATIVE CONSTRUCTION COST BETWEEN THE CONVENTIONAL GREEN-
HOUSE AND THE WASTE HEAT RESEARCH GREENHOUSE WITHOUT BACK-UP
HEATING SYSTEM
Conventional
9.1m X 21.9m
Greenhouse
(30 ft X 72 ft)
Waste Heat Research
9.1m X 21.9m (30 ft
Greenhouse
X 72 ft)
Difference
Cost of Materials:
per square meter
per square foot
per .4 hectare
per hectare
Erection Cost:
per square meter
per square foot
per .4 hectare
per hectare
Combined Cost:
per square meter
per square foot
per .4 hectare
per hectare
TABLE 13. PROJECTED
4.5 Gj/HR/
Conventional
Natural Gas:
per square meter
per square foot
per .4 hectare
per hectare
No. 2 Fuel Oil:
per square meter
per square foot
per .4 hectare
per hectare
$ 5,264.00
26.24
2.44
106,157.00
262,207.00
$ 1,600.00
7.96
0.74
32,267.00
79,698.00
$ 6,863.00
34.19
3.18
138,404.00
341,858.00
COST OF BACK-UP
.4 HECTARE (4.3
Greenhouse
0.00
$0.00
0.00
0.00
0.00
$0.00
0.00
0.00
0.00
$ 8,098.00
40.32
3.75
163,310.00
403,375.00
$ 2,532.00
12.58
1.17
51,062.00
126,123.00
$ 10,630.00
52.90
4.92
214,372.00
529,499.00
$ 2,834.00
14.08
1.31
57,153.00
141,168.00
$ 932.00
4.62
0.43
18,795.00
46,425.00
$ 3,767.00
18.71
1.74
75,968.00
187,641.00
HEATING SYSTEM WITH AN OUTPUT OF
MBTU/HR/ACRE)
Waste Heat Research
$ 2.15
0.20
8,500.00
20,995.00
$ 3.66
0.34
15,000.00
37,050.00
Greenhouse
33
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($4.92/ft2) cost for a waste heat greenhouse. Adding the cost of a
back-up heating system, the cost of constructing a waste heat greenhouse
would range from $55.15 to $56.56/m2 ($5.12 to $5.26/ft2) (Table 14).
This cost is equivalent to $223,027 to $229,126/.4 hectare (1 acre)
or $550,877 to $565,941/hectare for the construction of a waste heat
greenhouse compared to $138,521/.4 hectare (1 acre) or $342,147/hectare
for a conventional greenhouse. The waste heat greenhouse would initially
cost $84,506 to $90,605/.4 hectare (1 acre) or $208,730 to $223,794/
hectare more to construct than the same size conventional greenhouse.
TABLE 14. A PROJECTED COMPARATIVE CONSTRUCTION COST BETWEEN A
CONVENTIONAL GREENHOUSE AND A WASTE HEAT GREENHOUSE
BASED ON .4 HECTARE (1 ACRE) BACK-UP HEATING SYSTEM
Conventional Greenhouse
Waste Heat Greenhouse
Natural
per
per
per
per
square
square
meter
foot
.4 hectare
hectare
$
138,
342,
34.
3.
521.
147.
19
18
00
00
$
223
550
55
5
,027
,877
gas
.05
.12
.00
.00
No. 2 Fuel Oil
$ 56
5
229,126
565,941
.56
.26
.00
.00
Greenhouse Energy Requirements
The amount of energy required to maintain an adequate temperature
for greenhouse crop production will vary with location, type of green-
house, energy conservation measures, and crop but may range from 5.3 Tj
to 7.8 TJ/.4 hectare (5 to 7.4 billion Btu/acre) with about 6.5 TJ/.4
hectare (6.2 billion Btu/acre) being average (2). The average annual
energy requirement for .4 hectare (1 acre) in Fort Valley, Georgia, is
about 5.2 Tj (5 billion Btu). As previously mentioned, the minimum
greenhouse temperature may vary according to the crops grown; however,
the above greenhouse energy requirements are based on maintaining a
minimum temperature ranging from 12.8°C to 15.6°C (550F to 600F).
Current Cost for Energy
Cost for Fossil Fuel. Thirty to forty percent of the cost of
greenhouse crop production is for energy and is increasing everyday.
Most greenhouses are heated by natural gas; No. 2 fuel oil ranks
second.
The cost to maintain adequate temperatures for greenhouse crop
production will vary according to the kind of fuel used. For the Fort
Valley, Georgia area, the average current cost/Gj for natural gas is
$3.04 ($3.20/MBtu), whereas the present average cost/Gj using Mo. 2
fuel oil is $6.45 ($6.80/MBtu). Thus, the annual cost of fuel (6.5 Tj/
.4 hectare or 6.2 billion Btu/acre) when supplied by natural gas is
$19,760/.4 hectare (1 acre) or $48,807/hectare and $41,925/.4 hectare
(1 acre) or $103,555/hectare when supplied by No. 2 fuel oil.
34
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Projected Cost of Waste Heat. Although several suggestions have
been made, presently, no general conclusions are possible for what waste
heat should cost. One suggestion was made that waste heat should cost
$0.19/Gj ($0.20/MBtu) (1). However, perhaps a more realistic cost should
be based on the cost of retrofitting a power plant with a greenhouse
heating capability and allocating the cost of retrofitting to the power
plant or greenhouse operator, or both. Because each site is expected
to have different constraints, the break even cost for greenhouse opera-
tion is likely to be site specific and dependent on the market for green-
house crops as well as power plant variables.
The investment and operating cost will vary with different sites.
However, the jfterco demonstration project near Minneapolis, Minnesota
may serve as a model (3).For the Sherco demonstration project, the
calculated cost to deliver the warm water 1,067 m (3,500 ft) to the
demonstration greenhouse and return it to the cooling tower the same
distance was about $0.96/Gj ($1.02/MBtu)/.4 hectare (1 acre) based on
the projected installed pipeline cost of about $600,000 for a pipeline
flow rate of 442 1/s (7,000 gallons/minute). Also included in the
above cost to deliver the warm water to the greenhouse are the pumping
costs, $270/year, chlorination for bacterial slime control estimated
to be $550/year and total operating cost estimated to be $l,500/year/
.4 hectare (1 acre) greenhouse.
Projected Savings By Using Waste Heat. The projected savings in
cost of greenhouse crop production in this study is based on the cost of
$0.96/Gj ($1.02/MBtu) for waste heat as obtained in the Sherco demonstra-
tion project (3). As previously mentioned, on an annual basis the average
.4 hectare (1 acre) greenhouse in the U. S. uses 6.5 Tj (6.2 billion Btu)/
.4 hectare (1 acre), calculated to be approximately $19,760 or $48,8077
hectare when supplied by natural gas. This is equivalent to $4.88/m2
($0.454/ft2). The same amount of energy supplied by No. 2 fuel oil has
been calculated to be about $41,9257.4 hectare (1 acre) or $103,555/hectare.
This is equivalent to $10.34/m2 ($0.962/ft2). If waste heat can be supplied
for $0.96/Gj ($1.02/MBtu), the cost to maintain adequate temperature for
greenhouse crop production would be $6,240/.4 hectare (1 acre) or $15,413/
hectare. This is equivalent to $1.54/m2 ($0.143/ft2). This represents a
savings of $33,394/hectare of $13,520/.4 hectare (1 acre) when compared to
natural gas and $88,142/hectare of $35,685/.4 hectare (1 acre) when compared
to No. 2 fuel oil.
Since this study revealed that a waste heat greenhouse would initially
cost $84,506 to $90,605/.4 hectare (1 acre) more to construct than a conven-
tional greenhouse the same size, the number of years required to break even
is an important consideration in an economic analysis. Two important factors
in determining the number of years required to break even in a waste heat
greenhouse operation are the cost of delivered waste heat/Gj (MBtu) and the
kinds of fossil fuel waste heat is used to replace.
The effect of the cost of delivered waste heat on the number of years
required to break even is supported by the data in Table 15. In Table 15,
two other hypothetical costs for waste heat are compared with the cost of
35
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TABLE 15. ESTIMATED POTENTIAL ANNUAL SAVINGS IN ENERGY COST USING THREE PRICES FOR WASTE HEAT COMPARED
TO NATURAL GAS AND NO. 2 FUEL OIL AND THE NUMBER OF YEARS REQUIRED TO BREAK EVEN
CO
cri
BASED ON
COST OF WASTE
HEAT/Gj
$0.96/GJZ
$6,240
$1.50/Gj
$9,750
$2.00/Gj
$13,000
THE AVERAGE ANNUAL GREENHOUSE USE OF 6.5 T
COST OF ENERGY/
Gj SUPPLIED BY
NATURAL GAS
$3.04/Gjx
$19,760
$3.04/Gj
$19,760
$3.04/Gj
$19,760
COST OF ENERGY/
Gj SUPPLIED BY
NO. 2 FUEL OIL
$6,45/Gjw
$41 ,925
$6.45/Gj
$41,925
$6.45/Gj
$41,925
j (6.2 BILLION BTU)/. 4 HECTARE (1 ACRE)
SAVINGS OVER
THE USE OF:
Natural No. 2
Gas Fuel Oil
$2.08/Gj $5.49/Gj
$13,520 $35,685
$1.54/Gj $4.95/Gj
$10,010 $32,175
$1.04/Gj $4.45/Gj
$6,760 $28,952
YEARS REQUIRED TO
BREAK EVEN
THE USE OF>'
Natural
Gas
6.2
8.4
12.5
OVER
*
No. 2
Fuel Oil
2.4
2.6
2.9
is estimated that a waste heat greenhouse will cost $84,506 to $90,605 more/ .4 hectare (1 acre)
than a conventional greenhouse.
zThe cost of waste heat/Gj is based on the Sherco demonstration project.
xThe cost of natural gas/Gj is based on Fort Valley, Georgia's (1979) price.
wThe cost of No. 2 fuel oil is based on Fort Valley, Georgia's (1979) price.
-------
waste heat/Gj (MBtu) established by the Sherco demonstration project (3).
Regardless of the kind of fossil fuel replaced by waste heat, there is
an increase in the number of years required to break even as the cost
of waste heat/Gj increases.
Since different fossil fuels vary in cost, it is obvious that the
number of years required to break even in a waste heat greenhouse
operation is greatly determined by the cost of the fuel replaced by
waste heat. As illustrated by the data in Table 15, the cost/Gj of
heat supplied by natural gas and No. 2 fuel oil is $3.04 and $6.45,
respectively. With waste heat costing $0.96/Gj, it requires 6.2 years
to break even compared to 2.4 years for No. 2 fuel oil for a .4 hectare
(1 acre) waste heat greenhouse. Should the price of waste heat increase
to $2.00/Gj, the number of years required to break even if waste heat
is used to replace natural gas is increased to 12.5 years as compared
to 2.9 years for No. 2 fuel oil.
It is important to note that inflationary fuel rates and increased
fuel costs were neglected in computing the above number of years required
to break even by using waste heat to replace natural gas and No. 2 fuel
oil._ Based on past trends, it is safe to expect inflationary fuel rates
and increased fuel costs to continue and thereby reducing the number
years required to break even by operating a waste heat greenhouse. Con-
sidering the current increasing costs of the two above fossil fuels,"the'
number of years required to break even for the cost of retrofitting can
probably be reduced to 3 to 4 years for heating by natural gas and 1 to
2 years for heating by No. 2 fuel oil by 1985.
MARKETING STUDIES
Bedding Plants. Marketing studies began on April 6, 1979, and con-
tinued throughout the bedding plant season. Bedding plants were sold
directly from the greenhouses. Browallia, coleus, impatiens, marigolds,
pansies, petunias, salvias, and verbenas were sold at a wholesale price
of $4.00/32-plant flat.
Customers did not show preference in buying plants grown in the con-
ventional greenhouse over those grown in the waste heat research green-
house. The quality of bedding plants grown in the waste heat research
greenhouse was equal to the quality of those grown in the conventional
greenhouse.
Bedding plants are usually grown in flats. A .4 hectare (1 acre)
greenhouse will provide the space for 21,840 flats, 0.56 m X 0.28rri (22 in
X 11 in). Petunias and marigolds are popular bedding plant crops and
were sold at $4.00/flat. This represents a gross return of $87,360
.4 hectare (1 acre) or $2.00/0.3 m? (/ft2).
Foliage Plants. Foliage plant crops are grown and sold in many
different pot sizes. However, this economic study is based on a 0.08 m
(3 in) pot size. Hypoestes sanguinolenta (polka dot plant), Caribbean
37
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begonia mix, and Dizyotheca elegantissima (false Aralia) can be easily
grown to a saleable size within 4 weeks and can serve easily as late
spring or early summer crops. A .4 hectare (1 acre) greenhouse can pro-
vide enough space for 599,040 0.08 m (3 in) pots.
In this study, the above plants grown in 0.08 m (3 in) pots were
sold locally to a supermarket at $0.50/pot which was the wholesale price.
If all 599,040 0.08 m (3 in) pots could be sold at $0.50/pot, the gross
return per .4 hectare (1 acre) greenhouse would be $299,520 or $6.88/
0.09m2 (/ft2).
Certain foliage crops will probably give the greatest economic
return due to rapid crop turn over.
Potted Chrysanthemums and Poinsettias. Although experimental data
were never collected for chrysanthemums and poinsettias during the fall
of 1978 (because the greenhouses were not completed in time), they are
commonly grown as fall greenhouse crops. The average wholesale prices
in 1978/0.15 m (6 in) pot of chrysanthemums and poinsettias were $2.17
and $2.47, respectively (6). In this study, poinsettias are being used
as the fall crop for economic evaluation.
Poinsettias are normally grown in 0.15 m (6 in) pots. It is custo-
mary to allow 0.09 m2 (ft2) for each poinsettias pot base. The estimated
crop value is $53,797/.4 hectare (1 acre) or $1.24/0.09 m2 (/ft2).
Economic Incentive to Use Waste Heat. Based on the above annual crop
rotation, the projected gross income for a greenhouse operator is $440,677/
.4 hectare (1 acre) or $10.11/Q09m2 (/ft2). If waste heat can be bought
at $0.96/Gj ($1.02/MBtu), a greenhouse operator can expect to save annually
$13,520/.4 hectare (1 acre) or $33,394/hectare when compared to heating
with natural gas and $35,685/.4 hectare (1 acre) or $88,142/hectare when
compared to heating with No. 2 fuel oil. On a /0.09m2 (/ft2) basis, the
estimated savings are $0.310/0.09m2 (/ft2) when compared to heating with
natural gas and $0.819/0-09m2 (/ft2) when compared to heating with No. 2
fuel oil.
The above economic evaluation, however, is based on the greenhouse
operator selling all of the plants grown in a .4 hectare (1 acre) green-
house and receiving top prices for each crop which is rarely the case. If
a greenhouse operator is unable to sell all of the plants produced for top
prices, the need to save on the cost of fuel becomes even more essential
to a profitable operation. Admittedly, it takes slightly more electricity
to operate a waste heat greenhouse than it does to operate a conventional
greenhouse. This added cost for additional electricity which is required
to operate the fans and back-up heating system in a waste heat greenhouse
is not included in the previous economic analysis. However, with a saving
in the cost of fuel ranging from $13,520 to $35,685/.4 hectare (1 acre)
or $33,394 to $88,142/hectare along with the scarcity of fossil fuel, it
appears that the utilization of waste heat in the greenhouse production of
high cash valued ornamental crops can be economically feasible.
38
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REFERENCES
1. Beall, S. E., Jr., and G. Samuels. The Use of Warm Water For
Heating and Cooling Plant and Animal Enclosures. 1971.
ORNL-TM-3381
2. Berry, James W., and Herman H. Miller. A Demonstration of
Thermal Water Utilization in Agriculture. Environmental
Protection Technology Series. EPA-660/2-74-011. April, 1974.
3. Boyd, L. L., G. C. Ashley, J. S. Hietala, R. V. Stanfield, and
T. R. C. Tonkinson. A Demonstration of Beneficial Uses of Warm
Water From Condensers of Electric Generating Plants.
EPA-600/7-80-099, U. S. Environmental Protection Agency, Research
Triangle Park, North Carolina, 1980. pp. 53.
4. Burns, Earl R., Robert S. Piles, and Carl E. Madewell. Waste
Heat Use In Greenhouses. State of the Art, Waste Utilization
for Agriculture and Aquaculture. TVA and EPRI. August, 1978
Section 3: pp. 1-58.
5. Census of Agriculture. USDA. 1974. pp. Ill 38-39.
6. Crop Reporting Board. Floriculture Crops: Production Area
and Sales, 1977 and 1978, Intentions for 1979. Economics,
Statistics, and Cooperative Service, USDA, Washington, D. C
March, 1975. pp. 2-27.
7. Jensen, Merle H. The Future of Energy-Sources, Ideas. In:
Proceedings of the Tenth International Bedding Plant Conference
Bedding Plants, Inc., Denver, Colorado, 1977. pp. 214-238.
8. Madewell, C. E., L. D. King, Johnny Carter, J. B. Martin, and
W. K. Furlong. Progress Report: Using Power Plant Discharge
Water in Greenhouse Vegetable Production. Bull. 1-56.
Tennessee Valley Authority, Muscles Shoals, AL. January, 1975.
9. Olszewski, M. and H. R. Bigelow. Analysis of Potential Imple-
mentation Level for Waste Heat Utilization in Nuclear Power
Industry. ORNL, October, 1978. pp. 1-27.
10. Steel, Robert G. D., and James H. Torrie. Principles and
Procedures of Statistics. McGraw-Hill Book Company, Inc.,
New York, 1960. pp. 132.
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