• TABLE OF CONTENTS
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 Copyright
 Title Page
 Table of Contents
 Introduction
 The solar heated water (hydronic)...
 How to figure your greenhouse heating...
 Sizing components for a solar heating...
 Economics and other considerat...
 Reference
 Worksheets
 Weather bureau maps






Group Title: Research report - Bradenton Agricultural Research & Education Center - GC-1976-3
Title: Application of solar heated water to greenhouses
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00067695/00001
 Material Information
Title: Application of solar heated water to greenhouses
Series Title: AREC Bradenton research report
Physical Description: 30 p. : ill., maps ; 28 cm.
Language: English
Creator: Lucas, R. F
Baird, C. Direlle ( Carl Direlle )
Agricultural Research & Education Center (Bradenton, Fla.)
Publisher: AREC, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Bradenton FL
Publication Date: 1976?
 Subjects
Subject: Greenhouses -- Climate -- Florida   ( lcsh )
Greenhouses -- Heating and ventilation -- Florida   ( lcsh )
Greenhouses -- Energy conservation -- Florida   ( lcsh )
Solar energy -- Florida   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 15).
Statement of Responsibility: by R.F. Lucas & C.D. Baird.
General Note: Cover title.
Funding: Bradenton AREC research report
 Record Information
Bibliographic ID: UF00067695
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 04017832

Table of Contents
    Copyright
        Copyright
    Title Page
        Title Page
    Table of Contents
        Table of Contents
    Introduction
        Page 1
    The solar heated water (hydronic) system
        Page 1
        Page 2
        Page 3
        Page 4
    How to figure your greenhouse heating needs
        Page 5
        Page 6
        Page 7
        Page 8
    Sizing components for a solar heating system
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Economics and other considerations
        Page 14
    Reference
        Page 15
    Worksheets
        Page 16
        Page 17
        Page 18
    Weather bureau maps
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida




(2C~


Application of Solar Heated Wter--.-.
HUI'L LIBRARY
to Greenhouses

SEP 28 1976


by R. F. Lucas & C. D. Baird


l.FA.S. Univ. of Florida,
* ''*^.*-J-SS W _i-iv- a^~.?sV=r,,y- "3XBW aiE.iSS:


AREC Bradenton Research Report, GC-1976-3
AREC, Bradenton
Institute of Food and Agricultural Sciences
University of Florida, Gainesville


r
'I I~f;ji












APPLICATION OF SOLAR HEATED WATER TO GREENHOUSES

1 2
R. F. Lucas and C. D. Baird2
IFAS, University of Florida
Gainesville, Florida






TABLE OF CONTENTS

Page

Introduction 1

The Solar Heated Water System 1
Principles of Operation
Heat Distribution to Greenhouse
Mechanical Equipment
Plumbing
Water Treatment

How to Figure Your Greenhouse Heating Needs 5
Fuel Consumption History
Heat Loss Method
Degree-Day Totaling Calculations

S-'ng Components for a Solar Heating System 9
Available Solar Energy
How to Calculate your Insolation
Collector Sizing
Heat Storage Sizing
Heat Exchange Sizing

Economics and Other Considerations 14

References 15

Worksheets 16

Weather Bureau Maps 19




lInterim Assistant in Agricultural Engineering, Agricultural Research and
Education Center, Bradenton, Florida
2Assistant Professor of Agricultural Engineering, Agricultural Engineering
Department, University of Florida, Gainesville, Florida



This publication was printed at a cost of $264.80, or 26.5 cents per copy, as a means of relating
research findings to the public.










APPLICATION OF SOLAR HEATED WATER TO GREENHOUSES


INTRODUCTION

With the rising competition for energy and the accompanying increase in
the cost of heating and cooling greenhouses, alternative energy sources
are gaining in popularity. One such source of energy is the sun. Its
heat may be harvested, stored and then utilized to heat or cool all types
of structures including greenhouses.

This report is based on solar energy conversion research at the
Agricultural Research and Education Center, Bradenton, Florida. Some
of the data presented herein is from other sources, and although not
subject to investigation at the Bradenton Center, is believed to be
accurate. This research was concerned exclusively with the application
of solar heated water to heating greenhouses. Although some of the data
herein may be applied to other structures, the authors caution that this
data is limited in application and should not be generally applied to
other structures without a detailed investigation of each specific
installation.

This bulletin shall explain:
a. How a solar heated water system works (page 1)
b. How to figure your greenhouse heating needs (page 5)
c. How to figure your equipment needs (page 9)

THE SOLAR HEATED WATER (HYDRONIC) SYSTEM

A typical solar heating system utilizing water consists of solar heat
collectors, a heat storage vessel, a means of heat distribution and
mechanical equipment to direct water flow (Figure 1).

Principles of Operation
Collector

Radiant energy from the sun is converted into heat when it strikes a
surface. Most of this energy, when striking a dull or black surface,
will be converted into heat and will raise the temperature of this
surface.

In order to prevent loss of this heat energy, the surface, called the
heat absorber, must be insulated. The side of the absorber surface away
from the sun can be insulated with any of several common insulating
materials. The side facing the sun must also be insulated by some
material which does not greatly reduce the amount of sunlight striking
the absorber. Glass is most frequently used as the cover for solar
collectors because of its ability to trap solar radiation. The air
space between the glass and absorber acts as an insulating medium, which
allows nearly all solar radiant energy to pass through and at the same
time prevents direct contact between the heated absorber and outside
air (wind).










APPLICATION OF SOLAR HEATED WATER TO GREENHOUSES


INTRODUCTION

With the rising competition for energy and the accompanying increase in
the cost of heating and cooling greenhouses, alternative energy sources
are gaining in popularity. One such source of energy is the sun. Its
heat may be harvested, stored and then utilized to heat or cool all types
of structures including greenhouses.

This report is based on solar energy conversion research at the
Agricultural Research and Education Center, Bradenton, Florida. Some
of the data presented herein is from other sources, and although not
subject to investigation at the Bradenton Center, is believed to be
accurate. This research was concerned exclusively with the application
of solar heated water to heating greenhouses. Although some of the data
herein may be applied to other structures, the authors caution that this
data is limited in application and should not be generally applied to
other structures without a detailed investigation of each specific
installation.

This bulletin shall explain:
a. How a solar heated water system works (page 1)
b. How to figure your greenhouse heating needs (page 5)
c. How to figure your equipment needs (page 9)

THE SOLAR HEATED WATER (HYDRONIC) SYSTEM

A typical solar heating system utilizing water consists of solar heat
collectors, a heat storage vessel, a means of heat distribution and
mechanical equipment to direct water flow (Figure 1).

Principles of Operation
Collector

Radiant energy from the sun is converted into heat when it strikes a
surface. Most of this energy, when striking a dull or black surface,
will be converted into heat and will raise the temperature of this
surface.

In order to prevent loss of this heat energy, the surface, called the
heat absorber, must be insulated. The side of the absorber surface away
from the sun can be insulated with any of several common insulating
materials. The side facing the sun must also be insulated by some
material which does not greatly reduce the amount of sunlight striking
the absorber. Glass is most frequently used as the cover for solar
collectors because of its ability to trap solar radiation. The air
space between the glass and absorber acts as an insulating medium, which
allows nearly all solar radiant energy to pass through and at the same
time prevents direct contact between the heated absorber and outside
air (wind).































































COLLECTOR
MODE


FIGURE 1. Plumbing schematic for solar heating system,
showing heat collector, water storage tank,
h nof nv -r-nnnre r 1 -- -









By circulating water through tubes in direct contact with the heated
absorber plate, heat is transferred to the water. The hot water transfers
heat from the solar collector to a storage tank for later use.

Hot Water Storage Tank

Since solar heat energy can be collected most effectively only during a
period of six to eight hours each day, some provision must be made to
heat enough water and store it to satisfy greenhouse heating requirements
for colder periods.

The following factors should be considered when selecting a hot water
storage system:
a. Water temperature (this report assumes operating water temperature
of 140F to 1800F)
b. Storage tank capacity
c. Storage tank insulation

The storage tank and all connecting piping must be well insulated.
Sprayed urethane insulation not less than 6 inches thick is recommended
for the storage tank. Urethane, fiberglass, or other suitable insulations
may be used to cover all pipes. If possible, no part of the system,
except valves, pumps and monitoring equipment, should be left uninsulated.

Heat Distribution to Greenhouse

Greenhouses already plumbed for hot water or steam heating may be
adapted to a solar heated hot water system. However, the size of the
heat exchangers (heating coils) and possibly the plumbing may need to be
increased for adequate heat transfer. This is due to the much smaller
temperature difference between the solar heat source and the air. Figure
1-illustrates.plumbing connections required.

Where a greenhouse is converted from forced air, or is not equipped with
a heating system, an underbench forced air heat exchanger is suggested.
Research has shown that underbench heating is also beneficial to plant
growth (1). An alternate method is to use an underbench hot water pipe
system. Where such a system is employed, skirting below the bench is
recommended.

Solar hot water heating is compatible with any present hot water or steam
system and is easily adapted to other systems. A greenhouse heating
reference book offers the reader any number of possibilities (2).

Mechanical Equipment

Figure 2 shows a reliable system for controlling hot water flow.

a. The Differential Thermostat, "A", controls the flow of hot water from
the storage tank to the collector and back to the tank., This
thermostat regulates solenoid valves 1 and 4, and the pump motor.

b. Solenoid valves, 1, 2, 3, 4, are opened or closed on signal by the
differential thermostat (A) or the greenhouse temperature controller












C Greenhouse DA rCollector
I ambient ,Tank
115 VAC



F B E E B
S2 S3 1 S4

D









A Differential Temperature Controller
B Solenoid Valves, Hot Water Type, 115 VAC Coils
C Greenhouse Temperature Controller
D Hot Water Circulating Pump
E DPST Relay 115 VAC
F Heat Exchanger Fans

Greenhouse Temp. Controller (C) Activated Solenoids (2, 3), Fan (F),

and Pump (D), when Greenhouse Ambient Falls Below Set Minimum

Temp., Circulating Hot Water from Tank Top to Heat Exchangers

in House.


Differential Controller (A) Activates Solenoids (1, 4), and Pump (D),

When the Collector Temperature Exceeds Tank Temperature, Circulatin

Cooler Water from the Tank Bottom to Collectors for Heating.


Solenoids (B) are Operated Directly from Controller Outlets. Relays

are Used to Isolate Pump (D) from Controllers (A, B).




FIGURE 2. Wiring schematic for solar heating system showing
solenoid valves, pump motor and thermostat wiring.









(C). Solenoid valves should be in closed position normally and
rated at 2000F or higher operating temperature. A wholesale
plumbing supply house can generally provide adequate valves.

c. A Greenhouse Temperature Thermostat, "C", controls solenoid valves
2,3 and the pump. This thermostat can be an ordinary temperature
controller.

d. One pump, "D", is used to direct the hot water flow to both the
collectors, and the heat exchanger or radiating hot water pipes.
The pump should have enough capacity to move a minimum of 4 gal per
hour per ft2 of solar collector area. Friction through the system
must be calculated to insure a proper flow rate with reasonable
pressure head.

e. Isolation relays, "E", are used to isolate each part of the control
system. Any heavy duty double pole, single throw (DPST) 115V, 60
H.Z., A.C. control relay will work. Refer to wiring schematic,
Figure 2.

All equipment described has been incorporated into the operational system
at the Bradenton Center. Although this equipment has proven satisfactory,
this is not an endorsement of any particular item or manufacturer. This
system is flexible enough to permit substitution of comparable euqipment.
All equipment incorporated into the system is "off the shelf," however,
it may be necessary to contact a number of suppliers to obtain all items.

Plumbing

All plumbing should be galvanized iron or copper pipe only.

Water Treatment

All water should be treated with corrosion inhibitors, and where necessary,
antifreeze solution.

HOW TO FIGURE YOUR GREENHOUSE HEATING NEEDS

There are two reliable ways to calculate greenhouse heating needs:
1. Fuel consumption history
2. Heat loss method
a. Hourly heating requirements
b. Degree-day totaling (monthly heating requirements)

Fuel Consumption History

Greenhouse heating needs are best determined by reviewing previous fuel
use. By knowing the amount of fuel used, and heating equipment efficiency,
an estimated maximum and minimum need can be determined.

Break yearly fuel costs into monthly totals reflecting fuel used each
month. Determine the number of gallons, pounds, cu ft. or k.w. of fuel











used each month and multiply each monthly total times the BTU figure in
Table 1. Worksheet 1, at the end of this bulletin, can be used to list
these monthly figures.

Table 1. BTU Equivalence of Various Fuels


Fuel Oil 143,924 BTU/gal
Kerosene 135,143 BTU/gal
Coal 11,800 BTU/lb
Natural Gas 1,000-1,700
BTU/cu.ft.
Propane 2,300 BTU/cu.ft.
Electricity 3,413 BTU/KW hr.

Source: CRC Handbook of Chemistry & Physics.

Heating equipment, boilers, space heaters, etc., generally operate at 70%
to 80% efficiency, therefore, the total monthly BTU figure from Table 1
must be corrected to reflect this efficiency. In the examples below,
a figure of 75% equipment efficiency is used.

This formula summarizes the way to use past fuel data to determine
greenhouse heat loss:

(Monthly Fuel Used) x (BTU Equiv.)* x (Equip. Efficiency) = (BTU needed)

EXAMPLE: A grower in Apopka, Florida, uses 500 gal of fuel oil each
January. His BTU needs are calculated thus:

(500 gal) x (143,924 BTU/gal)* x (.75 efficiency) = 53,971,500 BTU needed

Note that nothing was said about the particular greenhouse, insulation,
inside or outside temperature, etc. This is a very direct method and
should be used whenever possible to determine heating needs.

Heat Loss Method

This method of figuring heating needs is based on generally accepted
greenhouse industry data and formula. This is a very general method and
final sizing should be determined by a qualified heating engineer. This
method will aid in preliminary planning of a new greenhouse.

The heat loss method is accurate for common greenhouse structures; however,
it does not take into account:
a. types of unusual structures
b. method of insulating, if any
c. influence of surrounding land and structures
d. local climatic differences


*From Table 1









house orientation
quality and proper utilization of heating equipment
temperature differences within the house


The figures and tables cited in this example are based on "Standards for
Greenhouse Loss Calculation" prepared by the National Greenhouse
Manufacturers Association.


Example:
a. Assume an


aluminum framed glass greenhouse:
50' wide and 100' long
gutter height = 8 ft.
roof pitch = 6/12


b. Determine glass area*


Ends
Sides
Roof
Gables


A
B
B
(A)


Cx 2
Cx 2
Dx2
Ex2


50'
100'
100'
25'


x 8'
x 8'
x 28'
x 12,5'


= 800 sq. ft.
= 1600 sq. ft.
= 5600 sq. ft.
= 625 sq. ft.
= 8625 sq. ft.


TOTAL GLASS AREA


c. From Table 2, find the wall loss factor that applies to this type
of greenhouse structure. In this example, glass applies.
Therefore, multiply 8625 x 1.12 = 9660.

d. From Table 3, find the type of construction that best describes
this greenhouse. In the example we assume that the house is all
metal (good tight glass house, 20 or 24 in. glass spacing).
Therefore, multiply 9660 x 1.08 = 10,432 BTU loss per degree-
hour.

e. Now determine the average severe temperature difference (AT)
between the outside and inside. In the example assume a (AT)
of 30. Multiply 10,432 x 30 = 312,960, total BTU loss per hour
for this greenhouse.



*Subtract other wall areas not included in glass measurement and figurf-
their heat loss separately.










Table 2.* Wall heat loss factor (composite walls).


Material Factor Material Factor


Glass 1.12 8" Concrete .60
Transite 1.00 4" Concrete Blk .58
4" Concrete .76 8" Concrete Blk .46


Table 3.* Construction Factor.


Material


Factor


All metal (good tight glass house, 20 or
24 in glass spacing)

Wood and steel (good tight house, 16 or 20 in
glass spacing)(metal gutters, vents, headers, etc.)

Wood houses (glass houses with wood bars, gutters,
vents, etc., up to and including 20 in glass spacing)
Good tight houses
Fairly tight houses
Loose houses

Fiberglass covered wood houses
Fiberglass covered metal houses
Double glazing with 1" air space
Plastic covered metal houses (single thickness)
Plastic covered metal houses (double thickness)


1.08


1.05



1.00
1.13
1.25

.95
1.00
.70
1.00
.70


NOTE: Any wall areas constructed from material other than glass
should be calculated with the proper wall loss factor from
Table 2. Add this heat loss to the glass total above. Refer
to worksheet 2.



*Based on Tables 13 and 14, The Greenhouse Climate Control Handbook,
Acme Mfg., Muskogee, Oklahoma. Copyright 1975.










b. Degree-Day Totaling Calculations


By definition degree days are the number of days (24 hours) that there is
some temperature difference between a base temperature of 650F and an
actual outside temperature of less than 650F.

As examples:
It is 650F outside for 24 hours this is 0 degree days
It is 300F outside for 24 hours this is 35 degree days (650F 300F)
It is 650F outside for 12 hours, then 30F outside for 12 hours this is
17.5 degree days (650 30 = 35 for day = 17.5)

Average monthly degree days are calculated by the Weather Bureau for every
location in the United States.

Example

In the previous heat loss example, it was determined that the greenhouse
lost 10,432 BTU per degree-hour.

From the Weather Bureau map (total heating degree days) for January, it
is determined that the example greenhouse is located in an area where
January has 200 degree days. This figure (200 degree days) is multiple
by 24 hours to obtain 4800 degree hours.

Now multiply 10,432 BTU per degree-hour loss by 4800 degree hours to find
total BTU loss of 50,073,600 for the example month. Remember that this is
a monthly total and the grower will experience both warm and cool periods
which average out to this total. This figure is based on an inside
temperature of 65F and will vary for differing temperatures. The next
section will discuss how to size equipment to meet these needs.


SIZING COMPONENTS FOR A SOLAR HEATING SYSTEM

By following the procedures given below, a grower should be able to
explain his needs to suppliers and to determine if equipment proposed
for his operation will be suitable. The previous sections offered methods
of finding the BTU needed to heat greenhouse structures. In this section
a method of determining the size of the various components of the solar
heating system will be presented.

This report stresses the use of flat plate collectors for two reasons:
(1) the flat plate collector is the least expensive type at present,
and (2) flat plate collectors can catch both direct and indirect sunlight.
Direct sunlight is that which causes a shadow and indirect sunlight is
that which is available on a hazy or cloudy day.

Available Solar Energy

The amount of solar energy available is called insolation and is measured


-9-










at many locations in the United States by the U. S. Weather Bureau.
The U. S. Weather Bureau calculates insolation in langleys per day.
However, these figures must be converted to BTU to be useful in the
following calculations. For your calculations use: 1 langley per day
= 3.7 BTU/sq.ft.-day. The Weather Bureau figure is for sunshine
striking a flat (horizontal) surface. The actual amount of heat
collected per unit area depends on equipment type and orientation
toward the sun. Since the sun is rarely directly overhead, the solar
collector is more efficient if tilted with its glass face directly
toward the sun. Because of the sun's seasonal change in altitude, it
is necessary to set the collector angle in an optimum position to
receive the greatest amount of the sun's rays when needed most. It is
generally accepted that the angle between the horizontal and the
collector face should equal the latitude where the collector is located
plus 10-15 degrees. For example, a collector installed at Bradenton,
Florida (latitude 270) should have an angle to the horizontal of 370
to 420.

A number of things influence the optimum collector tilt angle. Season
of the year is most important. When the sun is lower in altitude
(winter), the solar collector must be tilted from the horizontal to be
more efficient. Other factors will affect the turn of the collector
from its normally south facing position. For instance, if morning
sunshine is obscured by fog in a particular area, it may be desirable
to turn the collectors slightly westward to benefit from the afternoon
sun. Perhaps in another area, afternoon thundershowers are of concern,
and the-collectors should be turned slightly eastward. Each situation is
unique and the operator must fully evaluate the pecularities of his
location before system installation.

How to Calculate Your Insolation

There are two general sources of insolation data readily available:

Insolation Maps. The Weather Bureau maps reproduced in this report show
measurements in langleys per day on a horizontal surface. Remember to
convert 1 langley per day to 3.7 BTU/sq.ft.-day. Where a grower's
location is such that a printed insolation number is not close, an
estimate must be made.

The local horizontal insolation figure, when converted to BTU, does not
consider the increased BTU gained by tilting the face of the collector
toward the sun. The actual value can be determined by multiplying by
the appropriate factor in Table 5, corresponding to your latitude and the
tilt angle used.

Example:

From the Solar Insolation Map for December, Atlanta shows insolation of
211 langleys per day. This figure times 3.7 BTU/sq.ft.-day (211 x 3.7)
is 780 BTU/sq.ft.-day. For this location (latitude of 340), with collector


-10-











tilted at 440 from the horizontal, (780 x 1.91) or 1490 BTU/sq.ft.-day
are available.

Insolation Table

Table 4 lists probable minimum and maximum solar insolation for a
horizontal surface at a given latitude for the months of December and
January. These months are generally most deficient in insolation.
Table 5 gives a correction factor for surfaces tilted to the south at an
angle equal to latitude (L) or latitude plus ten degrees (L + 10).

To find the available solar energy striking a tilted collector:
a. find horizontal insolation (Table 4) for a given month and
latitude
b, multiply by correction factor (Table 5) for a given month,
latitude, and collector tilt

Example: In Apopka, Florida (280 latitude) Table 4 shows that 921 to
1548 BTU/sq.ft. are available each day on a horizontal surface.

A surface tilted to the south at an angle of 280 (L) would receive 1.45
times as much energy (Table 5), or 1335 to 2244 BTU/sq.ft. each day and
a surface tilted 380 (L + 100) would receive 1.53 times as much energy
or 1409 to 2368 BTU/sq.ft. each day.

Example: From the Insolation map for January, it is determined that
about 325 langleys fall on a horizontal surface each day in Bradenton,
Florida; 325 x 3.7 = 1200 BTU/sq.ft. each day (radenton is at 270
latitude). Since Bradenton is located at 270 latitude, a tilt factor
of 1.5 (average between 1.53 and 1.47) is obtained from Table 5 for a
tilt of L + 10. This factor times 1200 BTU/sq. ft. per day is 1800 BTU/
sq.ft. each day (1200 x 1.5 = 1800).

Collector Sizing

The total collector surface required to furnish one hundred percent of
the heating needs for each greenhouse is calculated by multiplying the
total available BTU per day by the number of days per month and then
dividing the number into the BTU required to heat the greenhouse for this
same period.

Example: In the Bradenton example it was determined that the area
received 1800 BTU/sq.ft. per day for a collector inclined at L + 100.
Multiply 1800 x 31 days for January = 55,800 BTU/sq.ft. per month.
Assuming the greenhouse heating needs are 14,800,000 BTU for January,
then divide these needs by the available insolation per month.

14,800,000 BTU 260
55,800 BTU/sq.ft. 260 sq ft


-11-











Table 4. Horizontal insolation (BTU/sq.ft.-day)


January December
Latitude min/max min/max


24 1142/1696 1032/1622
26 1032/1622 958/1548
28 921/1548 870/1474
30 811/1472 744/1401
32 663/1401 678/1327
34 571/1327 582/1246
36 490/1235 494/1157
38 442/1142 409/1069
40 387/1032 346/ 995
42 331/ 940 287/ 899
44 294/ 840 228/ 803
46 272/ 737 176/ 715
48 235/ 663 136/ 626
Source: Algae Research Project, Sanitary
Engineering Research Laboratory, Dept. of
Engineering, Univ. of California, Berkeley,
June 15, 1954.


Table 5. Collector tilt factors.


January December
Angle (tilt) L L + 10 L L + 10

Latitude
24 1.34 1.42 1.40 1.50
26 1.39 1.47 1.46 1.56
28 1.45 1.53 1.53 1.63
30 1.50 1.58 1.59 1.70
32 1.56 1.64 1.66 1.77
34 1.64 1.73 1.76 1.91
36 1.73 1.82 1.87 2.05
38 1.82 1.91 1.98 2.19
40 1.91 2.01 2.09 2.33
42 2.05 2.15 2.26 2.49
44 2.19 2.30 2.44 2.65
46 2.33 2.45 2.62 2.81
48 2.48 2.60 2.80 2.97


Source: Derived from da
Handbook, Chapter 59.


ta, ASHRAE Applications


-12-












In this example 260 sq.ft. of collectors are required to meet 100% of
the heating needs for this greenhouse if the system were 100%
efficient. However, no system is 100% efficient. It is assumed that
most collectors available at the date of this publication are approximately
55% efficient.

To determine the total number of collectors required at 55% efficiency,
divide 260 BTU sq. ft. by .55 which equals 472 sq. ft. of collector
area required to meet the needs of this example.

By determining the amount of solar insolation available in a given area
and comparing this figure with the BTU requirements determined previously,
it is possible to estimate the solar collector surface area needed to
provide adequate BTU for a given greenhouse.

Summary of calculation for collector sizing is found on Worksheet 3.

Heat Storage Sizing

The amount of heat stored in the water is dependent on the amount of
water circulated and the temperature increase as it passes through the
collector. The smaller the amount of water to be heated the hotter it
will become in a given time period. A limit is reached when the water
begins to boil. It is not desirable to heat the water to boiling. As
the water temperature increases the collector efficiency decreases.
Therefore, high temperatures (above 1800F) should be avoided.

A large quantity of water will heat less rapidly and to a lower average
temperature thus offering the need for less insulation (this does not
mean that insulation should be neglected) and a longer heat "carry over"
from day to day. Note: The storage vessel must be well insulated.

Given a certain amount of water storage, it may be desirable to place it
in several small vessels instead of a few large ones. This allows
several storage temperatures to be maintained simultaneously. It has
the disadvantage of increasing tank area, thus necessitating more
insulation to counter the greater heat loss potential.

Water can store 8.2 BTU per gallon for each degree of temperature increase.
The following example assumes a 15 degree temperature difference for an
average day's heat need. The system will generally be 'drained' of heat
infrequently (4-8 times per month), lowering tank temperature by more than
200 each time. Tank temperature will generally rise more than 200
between cold periods. An advantage of having several storage tanks is
that if a minimum storage temperature is required, the tanks may be
introduced successively. A minimum design temperature for the storage
is necessary in order to size the heating coils, as illustrated in the
next section.


-13-











Heat Exchange Sizing


Heat exchangers for solar heating systems are sized using procedures
similar to those for conventional systems with the main difference being
a lower minimum design temperature. For conventional steam or hot-water
systems, the heating source is usually at a temperature between 1600F and
2300F, giving a minimum temperature difference (At) of 160-700 = 900F,
for an inside temperature of 70F. A solar hot-water system may have a
water temperature of 1600F at the beginning of the heating cycle, but the
heating coils must be sized on the basis of the minimum hot water
temperature. This minimum design temperature may vary with specific
applications, but a value between 90F and 1000F is recommended. If
100F is chosen, the thermal storage capacity is represented by (160-
1000) = 600F times the pounds of water. In this case the At for the
heating coil would be (1000 700) = 300F. Comparing this with the A t
for the conventional hot water system (900F), the solar heating system
would require a heating coil three times as large; or in the case of a
steam system operating at 220F with a At of 1500F (220-70), five times
as large.

It should be emphasized that the system designer must be familiar with
the specific needs of each installation.

Example: for calculating storage capacity:
8.2 BTU are stored in a gallon of water with a one degree temperature
rise
8.2 BTU/gal x 150F = 123 BTU stored in a gallon of water with a 150F
temperature increase

From the collector sizing section it was assumed that the December
heating requirements for the example were 14,800,000 BTU. To determine
storage capacity divide the BTU requirement (14,800,000) by the product
of the storage capacity per gallon for 150F increase (123 BTU) and the
number of days in month (31):

14,800,000 BTU = 3881 gallons of storage water needed
123 BTU x 31

To offer a 'margin of safety,' round this figure upwards to 4,000 gallons
of water storage. Remember that this is a figure for a test greenhouse
in Bradenton, Florida. Generally the higher the latitude the more
collector area and water storage volume required.

ECONOMICS AND OTHER CONSIDERATIONS

The present cost of solar heating systems and the present cost of fuel
indicates that one should consider the economics involved before
installing a solar heating system for greenhouses. For example, a
solar heating system with a capacity equal to that referred to in the
previous example (472 sq. ft. of collectors producing 14,800,000 BTU
per month) would cost at current prices about $5,000. Assuming that


-14-











the system would be used continuously for four months per year (varies
with location and crop), the annual value of fuel savings would be
less than $200 at current fuel prices ($3.00/million BTU). Of course,
this figure will increase as the costs of solar systems are reduced with
mass production and fuel costs increase.

The data and examples presented in this bulletin are based on actual
installation at the AREC-Bradenton, Florida. However, there are other
considerations to be made when implementing a solar heating system.

Where temperatures drop below freezing, some means of employing an anti-
freeze solution must be included. The transfer fluid should be treated
with corrosion inhibitors. All connections should be tight and where
dissimilar metals are used in the system, isolation couplings should be
employed.

It is probable that only a very large system will handle 100% of the
greenhouse heating needs. The grower should compare the initial capital
expense depreciated over not less than 10 years nor more than 15 years
against current and projected fuel costs. Initial capital expense will
generally be high; however, operating costs are extremely low. Some
balance of supplementing a present conventional heating system with a
solar hydronic system may be the proper approach. As fuel costs increase
and the solar heating system is depreciated, its size can be increased.

The Bradenton research has demonstrated two important considerations
most often overlooked in commercial operations. One, the greenhouse
should be tight, and where possible the upper triangle sealed off.
Second, all heat distribution should be kept as close to the crop as
practical. Where melting snow must be accomplished, auxiliary poly
ducting can be added toward the top of the greenhouse and employed only
as needed to melt snow or ice.

The information and recommendations presented in this bulletin have been
checked and reviewed by the authors and are believed to be correct.
Because each installation is unique, the representations made herein do
not constitute a warranty of any type. The reader is advised to review
his solar energy conversion plans with qualified engineering personnel
before construction.

The authors wish to acknowledge the contributions in this research of
Mark E. Tellam, Engineering Technician, AREC-Bradenton, Florida.


REFERENCES

1. Soil Temperature and Development of Cuttings and Seedlings of Tropical
Foliage Plants, Richard Poole and W. E. Waters, HortScience 6(5) Oct. 1971.

2. The Greenhouse Climate Control Handbook, Acme Engineering and Mfg.
Corp., Muskogee, Oklahoma.


-15-










Work Sheet 1

To determine greenhouse heat loss

by

FUEL CONSUMPTION HISTORY*


Total Heat Loss
Heating Fuel BTU Equiv. in BTU's
Months Purchased x (Table 1) x Efficiency *** u Per Month
**

Aug. x x =
Sept. x x
Oct. x x
Nov. x x
Dec. x x
Jan. x x
Feb. x x
March x x
April x x
May x x =


Make a separate fuel estimate for each structure if greenhouses
are widely unconnected and not serviced by a central boiler.


** Check with fuel supplier if unable
Use gal., cu. ft., lb or KWH.


to determine from records on hand.


If equipment efficiency is unknown use .75 (75%) for new equipment
and estimate a lower percentage of older equipment.


-16-








Worksheet 2

To Determine Greenhouse Heat Loss

by

HEAT LOSS METHOD*


Width (A)
Length (B)
Gutter height (C)**
Other Wall material (C1)
Gutter to peak length (D)
Height of gable (E)

Calculate:


end A x C
side B x C
roof B x D
gabl (1A) x

from Table 2


E
Total area


BTU Loss


2
2-
2
2

x

=.
(x


from Table 3
Total Corrected BTU LOSS
Determine severe T
Total BTU Loss per hr at T


Now make same calculations for parts of structure not constructed of glaos -
add this total to total in line 11 above.



* Make a separate estimate for each detached greenhouse
S* Glass only


-17-


~--~---"












Worksheet 3
To Determine Collector and System Sizing

A worksheet should be made for each heating month

1 2 3 4 5 6
0.55 x
Total Total
Daily Number Available Total BTU Available Sq. ft.
Insolation* days BTU/sq ft req'd to BTU/sq ft Collector
Mo. for L + 10 x per month = month heat G.H. 7 month = Needed


Sept x =


Oct x =


Nov x =


Dec x =


Jan x =


Feb x = =


Mar x =


Apr x =


*From maps, Tables 4 and 5


-18-





Source: Climatic Atlas of the United States
U. S. Dept of Commerce
Environmental Data Service
June 1968


t's.Ita .0* ls.


125 20 U9S* .1000 7e0 is* 5 S
NORMAL TOTAL HEATING DEGREE DAYS, SEPTEMBER
i00 a400i400, (Base 650)




400 Bismarck Fargol 3 t S Ste. Marie 2o o
i o teraoa l /^in ^- 'ton
B0 ocojd A


I \ HT ^ u n Gren ny oo 100\
Ct 2 nlodid City Hurone\du lo
Sder LansinlK.





i -I0 l 0 4I\
0 emmc 20 Dubulao0 DetroitCity o 50

S2 roSL--tt let North PDet Moine\ s ./ 1 \











; Salt bNorth e Is S Jar^ \ ^
SNOTE.-CAUTION SHOULD BE


















IUSED IN INTERPOLATING OH
THESE GENERALIZED MAPS,
SHonol ull E30-YR. PERIOD, 1931-60 emphi



I Fort Worth City

v1035 00
















ol SI"y - Oklahom City 1 0-:1
Do New Orleanl





5125KoSED IN INTIRtLATING ON


oL hue THSE. APS ARE BASID ON .

\ IIT COA IGN SH L B E S E 0 M

61 sPu I. Venn cro Honolulu cm. K&r Io hn THEAERIOD, 1931-60.








so NORMAL TOTAL HEATING DEGREE DAYS, OCTOBER
at L,(BaseI6 650)

at"inonal Fa.lls








S/ e00 n S. Ste. Marie



















r alt o eo a Dei MoinesU SED Chi0a IN IWZdOLATXNG ON

















,P ,TH 30-YR. CTKIOD. 1931-60.
o H -- -b---o
...........ndiai ns iSCo ield hno





















200 _00_ _Dd_ |C A_ __one____________e_

-.._____ _0 L ___.__.------O --om Ct -_ ._ ....
00n nr
































Source: Climatic Atlas of the United States
U. S. Dept. of Commerce











S1 NOTE. --CATIO~ HOULD BE



:odis .oL lu _THESE -APS AR BASED ON
' "400 600 4L C hiSLAN ADS I
'Salt nWe i a:1 1/11 11

e i$ e0 1 05 0oo Ps so 5 8 *7












0U. S. Dept. of Com)erce

Environmental Data Service
St. Lo L RT.c.h- 1 OLO












1203~ nL


~ II -- __


'23 (N


I's


0Ir


log 1.~


IM$"


ar


r


or





I5' ^25 0 11' 7 05'3 's 4 *
S7 -----NORMAL TOTAL HEATING DEGREE DAYS, NOVEMBER --

/D 00o-I ---20----- (Base 650)
00.-1. l i.ubuquoro,


12 %00O


6 / L sfe o st.-x e




0I C eat Shee o Jc '*
0 c--- -- -- 1-"
-awns C / / DelR nAn
80 qe op ki m Cty City .o b














40 L _a ea o0
Ir B/ Lansing 0









S 0- NOTE. --CAUTION SHOULet o
on .... \ a IDes \ nes 5












Sch I alUSE IN INTERPOLATING ON
1434 townsi CO THESE GENERALIZED MAPS, i
Bethel G U F OF PARTICULARLY IN MOUNTAINOUS

Lihe THESE MAPS ARE BASED ON I
i .1.921 S4 0 C76
3nDodge City 9





















I L- "* -- ,----'-- '4' w o e ^IcOnvI-o --- 1lI.

4 Boo .*0 6JI



Source: Climatic Atlas of the United States
L. S. Dept. of Commerce
Environmental Data Service
June 1968
June 1,968




1Hi 4Yt isvIa.r1


NORMAL TOTAL HEATING DEGREE DAYS, DECEMBER
~n~z_ I-,L ~ .(Base 65*) 1 --~



a, rWO if
M'OBismarck I So. ma rieMu




P I cty n I W OT, b



a I S~t Lake Norrth) latts Des Mo' 9
Un I.) COMO



st. Lo exigt cb
ged City


C~ C
LkteRcs' at
Wile axr i Y .. W~~l~~~c- ~-/-~
F..Wor
4 lneihrvpot jgk j0



600 00 pOrleJcans 2.00o


_j ",,'400e~n 20
I Saf A Io

64 '5A 10
&a 10 NOTE.--CAUTION SHOULD BE
O~ethel0 F THSE GENERALIZED MYAPS.
d 15 G U P RTICULARLY IN VOUNTAiNOUS
~iDI AREAS.
odt&IL THESE APS ARE BASED ON1
17 a l .Aonuuu uul THE \ 30-YR. PERIOD, 1931-60.


?rlr ak =&I I~o~a
1~ 10 in.. I I( I ~l'OY1 I(L~lCII* IIIDOH LL~I LIA- L OUAL 110.*l~~l i~
176 1Y Y'o 1 Y II\ LPTRMRC 2 .106Ile


S- m I ,

Source: Climatic Atlas.of the United States
U. S. Dept. of Commerce
Environmental Data Service
June 1968


I I


I




















































n


Source: Climatic Atlas of the United States
U. S. Dept. of Commerce
Environmental Data Service
June 1968


______ ItS* ___ 5 0 120 ________ its* no* 105* l00* 95* 90' A' ao* 73* 70. g" *
/T^?^^''; -- ^^NORMAL TOTAL HEATING DEGREE DAYS, JANUARY

spok. 7 ..(Base 650 )o
SP-k 000
**** natIoa Falls
s or a Jill, ill ston 1800 A
12
Marie 1600e
.- 12 ^ ^ I00 T400 StB?-iarnar rg sin "o S. Ste.. Miri00
00 ing 00 gon 00\
urns 16661A0
1 Minneapolis 1600" 1
Green
I tt
: 110 1400
I / C 2tC. .I der 12 L-ansin- o o
00 0 1 .04 North Pobh


60o 14 K a a 00Citet oi
SaSt Ioi Ue oxinsto Uta ""OSbc
e Dodge North Pl a tt
2PO ~~~Lince. Clrnu



L' .. \00
Or 0 \00 1r0\



Arp uq rq rnrlo O tl Rc* 4
I Ci Cit



'S. -d imiga hre


Abio ene~l FotWrt rveot Jako
Dodg C0o





S------- ------
4w O1200n 20

In~ea~ t. DeRna io S kanAno 10 *hs80
YOM inP-


4nne Fort Worth
Abilene 0 grvpr ~ko 400















'F 7 Lt \ thue THESE MAPS I lE BASED O2
*t.Paul I., yy to \ ^- ^ o' ^onclulu o-k Kabului THE 30-TEAR PERIOD, 1g31-60
i* ~- rV ly ai i.s* .a s^c e esC
old 14 Dcey s o oo
J1 ~ / Lklio San.A t









S-- N irba s 10
18791 I


163 I'ac 01 r69 10USED IN INTERPOLATING ON
"Bethel 0 F F M E X I C0TEEGENERALIZE~D MAPS,
.'ard"4% 01 6- IGU L PARICULARLY IN MOUNTAINOUS
~cfD AREAS.
.1A Lihut TESE MAPS ARE EASED ON
t~au Oo l 96 ahlu HE 3 -YES B RIO, 1931-60

old 1".. or 6'r n r* ae
L& AI SAL I1.0100Po.
IU lAr koe onm
.4 I yI n I It r Ir; I PVX VOICE)A


"-


Ir









a









,e









a


I







/, NORMAL TOTAL HEATING DEGREE DAYS, FEBRUARY
/ly^^y, '(Base 65)
k / I -- .. nte
, 600 l / ,.-1200 -- 0. "" rntern-tiona FallFils1 J
ei Poet a 1, 4 00 sn 1i. t00 1 00

0 Bismarck Fargo D S. Ste- Mare o




90 and, "- r-- eNo Lo




s/ 4 ..00 1'd C N 80d 00 ... .
S S6 14 !od Hurn 9A .. t-0



















I I _o ix1 a rn .\ Bro n 1l00 C 0 *oor._. USED IN INTERPOLATING ON
~ I *Bthel I /\ \ 1 G U. O. -" I C ULRLY IN MOUNTAINOUS








/ THESE MAPS ARE BASED ON
,P."l I o_,s. ,--ol lu-r /ul. .\" THE 30-YR. PERIOD, 1931-60.
SI't '---"^ 10 i, 5 L I


oU. S. Dept of Commerce
1June 1968
Ifileno tol i {.




1000 "75 Ifi '.. .
-------- ,
Source: Climatic Atlas o t U eSe00
Envitle roRock Dt tS e
Abilene 1968
30, :Shre so son HOUO B




o.Sh~ PS 100 un
190, 200 200.
1 100 50








;old BV SS h





125s, .o0 W20' _it 11' Os 0* 95* go 5o' 7 05
'oo /NORMAL TOTAL HEATING DEGREE DAYS, MARCH
o o (Base 65' )
10 -'-apa international Falls
/ Williston I M IM


120 n 0 0 04 1 \ I o

I20 0 I e go BDu \ a T


.. eeb' (000 jPRad City Huron X" u
...... Lanin
80 00 0 .. ..o

oa i u b e 0
L_ 2 / e el U1i1

8000 Linal C


4. .. V To t
is 600 0Dodes C ity Chicst




























,,00,- ,oy- o 6.... 0i "



Source: Climatic Atlas of the United States
Environmental Data Service
June 1968
/5 1 o0 11 C.1






u THEE AP AEB

1 7 s0 0 -Fo v* i F 'F W W I d
00 1







s* 2o S' 110" I 0 __*__oo* _s_ _s* _oo* _* Is*
















"'* '* "- *"* '4-*^-f^ J;0 -**--------------- !,, Tf ,^ -
*&Oo NORMAL TOTAL HEATING DEGREE DAYS, APRIL \

-- o (Base 650)


8 0! sv E \oR I






,'00na t i. .....--on.--l
IS9 9Bismarck Fargo' Dul 00 P D



000D es ties "
Minneoln t ..







S t00 I Salt \ e y --- __ o o --------------l--b
Server X
400 Cit 60,. in0s City 600


4 00 ..0 0. I S Lou.... L 2 o h o d*



Amarilo Boo Du
Z,0I ey_ i I N;I: ""I- \V















.o..-USED IN INTERPOLATING ON
Bethel G F




,. A ..RCTIC ..l. .io SE8lr, T r, P,





Pa ,' p.. -M.. .st" NO TE.... .., .SHO.LD..
0B I 00USE 40n INEROATN ON








.. .. -8 .... .. F F'- PUERTO ICO UAND VIRGIN ISLAINS
t, Amarillo I AE
'ego' Ltle Rock Atlanta6 so


,Aew urn. tOt



















i 1 1L -P7m 9',1 ~


Source:. Climatic Atlas of the United States
U. S. Dept. of Commerce
Environmental Data Service
June.1968


,I -,


-A a





































































-r JI
Source: Climatic Atlas of the United States
U. S. Dept. of Commerce
Environmental Data Service
June 1968







-MEAN DAILY SOLAR RADIATION (Langleys)

~--6
"'o UM i NUBV1~



26 -4.
-. ,i -,,C~~~L-
.276> .. -. 66~




i I ; .

SI. .I a11 ) '-

Ii..
..frhX2l
-_j -3n .254 :

4 3 35 0---A,351




I-..
L~~iiu, ______ .. "- z __________
-i rT~-'00















TEAN DAILY SOLAR RADIATIONLateY)
'00~ DECEMBERR
/s ,)r I'D 96 ?l
Ii, ~ ~ ~ ~ --1- *9 ...:,~I* Oi~a


/ .....Y ii A-"~--r --- .-
















1J. Tlj


1 I Ii 'fr
FT
i 22


Source: Climatic Atlas of the United States
U. S. Dept. of Commerce
Environmental Data Service
June 1968


-28-











































































-_It
Source: Climatic Atlas of the United States
U. S. Dept. of Commerce
Environmental Data Service
-29- June.1968


MEAN DAILY SOLAR RADIATION (Langleys)

"" : JANU4 Y









.-... .





-2
.





-..-. MEAN DAILY SOLAR RADIATION (Langleys)






.. APRIL \




























j-


Source: Climatic Atlas of the United State





















U. S. Dept. of Commerce

-30- June 1968.
--- -- -- -- -


























_30 June ^SS
30".`J
33




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