Moisture egntent

Temperature - °C Depth - cm cm / cm
0
22 28
a ae
L 40 4
P| > ——~_ 34 |
L 60 4

L 80 RN |
D b 100
38

L 4 -40
34 120 42

—L.

30 r 140 4

L 4 42
ee ee ee
r 180 +

22 44

T T ¥ 200 t T T
0 20 40 60 70 0 20 40 60 70

Horizontal distance from pipe - cm

Figure 5. Temperature and moisture content distributions for
a pipe spacing of 140 cm and a pipe depth of 100 cm and average
monthly weather data and condenser discharge temperature (41C)
for Portland, Ore. in August. Simulation is for 31 days of
operation.

12




The friction factor for a smooth pipe is:

fv 0.014

The pressure drop is:

2
apMe k
ap= ph 5
2
. 1)(1740)2 10000
ap = .014 oyC go)" 1.27

AP = 170,000 g/cm (58Psi)
The pumping requirement, W, for 100 m of 1/2" diameter piping is:

mAP/p = (2200) 0.7 x 10°
37.4 Watts

=
"

The pressure drop for a 1" diameter pipe is:

2
(435 10000
-017 30980) 2.54

6461 g/cm? (2.2 psi)

AP

The pumping requirement for 1" diameter piping is:

W = 1.42 watts/100 meters

The pumping requirement for a 2" diamter pipe is:

W = .05 Watts/100 meters


Depth from soil surface - cm

21.7 O

© 22.5

© 26.6 26 25

48

T T T T

t—T — —T
0 4 8 12.16 20 24 28 32 36 40

Horizontal distance from pipe - cm

Figure 1. Comparison of calculated temperature (°C)
with experimental values from Sepaskhah
(1974).


LLZ0° LEE0" gol 66°L vol Sul 09S
L6E0° 6950° OL°E Le°Z 2°82 2°02 082
8€90° 980° oss eure Ole 9°S9 OvL
asniny
£910" S20" 9L°L vil 2L°0 2v'0 09S
7920" 98€0° €8°2 vo’? 98°0 2S°0 082
€Lv0° vE90° 90°9 eL's 6L°2 80°L OvL
Agenuee
(Wid / wd) (9.) aseassuy Jove aAOgY
aseausuy faun§s Loy “aAy dual “aay LOS JO JUadUag
OOL 0s OOL 0g OOL 0s (wd)
(wo) yzdag adtd (wo) yzdag edid (wo) yydagq adid BuLoeds
“Hiddd WI 002 OL O Y YO4 SLIZIAF WALSAS NOILVOINYI ONY ONIWYWM TI0S “2 alge

16




Sections

II
Ill
IV

TABLE OF CONTENTS

Introduction
Conclusions

The Soil Warming System
Results

References

Page


“wo OG SL Yydap adi

"OL6L S"UULW SLNed “3S UL Yadap WO OZ 7e UOLZeLWeA auNQeuaduiay jenuUy ‘pL auNBLy
HLNOW
Lf, NX, 9,85, ¥, ©, ef , Ww, v, Ww, dy et
0
pazeayun
[ S
Bufoeds wo gol
BuLoeds wo OpL F OL
r SL

F 02

do - aunzeuaduiay

25


Depth from soil surface - cm

42

180 q

200

T T T T T T
0 20 40 60 80 100 «120 «140

Horizontal distance from pipe - cm

Figure 6. Moisture content distribution for a pipe
spacing of 280 cm and a pipe depth of 50 cm for
average monthly weather data and condenser discharge
temperature for Portland, Ore. in January. The
simulation is for 31 days of operation.

13




9bvE0° 1090° o9°L 29° eo o°sL 09S

0v90° LOL* 69°€ Slt 2°82 8°9€ 082
1660° vel” G9 %0°6 eed 2°€8 OvL
L€20° €2v0° L6"L eye 9b°0 78°0 09S
S80" $S90° SO°E ee" 85°0 vl 082
€290° vol” 91°9 66° og*L 9L°2 Ovl
(wio/,wo) (99) aseauouy Jove aAOgy
aseauouy aahigs | “aay “dual “aay [LOS JO JUadVaq
OOL 0S OOL 0S 00 i} (uid)
(wo) yydag adig (uid) yzdag adig wo) yzdag adig BuLoeds

ysnbny

Aaenuee

“HLd3d WO OOL OL O VY YO4 SLOZIAF WALSAS NOILVOIUYI ONY ONIWYYM 10S

“Larger

15


q = 0.22 cal/cm-sec

To estimate the pumping requirement the water flow rate was calcu-
lated from an energy balance:

q = the Gy

Since it is desirable to minimize axial temperature gradients to provide
effective soil warming, the temperature gradient qr is chosen to be small.
For this calculation a 1°C temperature drop in 100 meters is chosen.

The water flow rate is then:

dT)-1
a(cg,)

1

(.22 cal/em-sec) [(1 cal/g-C) (1°/10000 om)]7!
2200 g/sec (4.9 Ft?/min)

For a 1/2" diameter pipe the average velocity is:
v = m/o, = 1740 cm/sec (57 Ft/sec)

The viscosity of water at 40C is:
v = 0.008 cm/sec

The Reynolds number is:

Rey = VD/v = 1740(1.27)/.008
2.7 x 10°

26


irrigation at the pipes even though the irrigation rates were the same.
Furthermore, it is expected that prolonged operation of a soil warming
system with no irrigation at the pipe would result in drying near the
pipe. Rykbost (1973) reported a very dry region (Moisture content equal
to 0.09 em?/em?) from 0 to 2 cm from the heating pipe for soil warming
in an open field with surface irrigation. The computer program does not
predict this because the node size is 10 cm and moisture content is
approximated by one mean value over the 10 cm x 10 cm volume. Reduced
moisture content at the heating pipe reduces soil warming because
thermal conductivity decreases with decreasing moisture content.

Subsurface irrigation offers additional benefits in the form of
reduced water consumption. Hanson and Williams (1968) and Hanson, et al
(1970) report production of equivalent yields of cotton with 25 percent
savings in water consumption using subsurface irrigation instead of
furrow irrigation. Zetzsche (1964) and Newman (1965) reported 42
percent water savings in growing cotton with subsurface irrigation.

Incorporation of a subsurface irrigation system with the subsurface
soil warming system is recommended since irrigation at the heating pipe
increases the warming of the soil and reduces water consumption. A
simple method of providing both heating and irrigation would be to
locate a small porous pipe for irrigation over a larger heating pipe.
The use of two pipes -- one to irrigate and one to heat -- should not be
much more expensive than soil warming with surface irrigation since
surface irrigation also requires piping. The subsurface irrigation
system is a permanent installation, therefore labor costs for operation
should be minimal and tend to offset the higher capital outlay. Potential
problems, such as root clogging of the irrigation pipe and maintaining
the desired irrigation flow rate, are not considered insurmountable
obstacles to successful operation.

10


range from $24,000 to $72,000 per month per acre. The expenses of
electrical soil warming in a greenhouse would be somewhat less but still
of the same magnitude as for open fields. Use of electric power plant
waste heat for soil warming is comparatively inexpensive and uses energy
that would otherwise be wasted. Closed-cycle condenser cooling water is
particularly attractive because the temperature is usually considerably
higher and more constant than open-cycle flow. This allows for better
design and greater effectiveness. Use of power plant condenser cooling
water for soil warming does have the disadvantage that the need for soil
warming is greatest when the condenser cooling water temperature is the
lowest, i.e., in winter. However, the condenser cooling water will
provide heating throughout the year.

Installation of a soil heating system requires a large capital
investment and the economic breakpoint depends on achieving the optimal
design, or layout, for the crops to be grown. Some field performance
data are available, which when incorporated with a mathematical model of
heat and moisture flow (Sepaskhah, 1974) permit examination of the
performance of alternative designs. This paper examines some alterna-
tives for several climates in the United States. It is not intended as
a detailed design manual for any one field or location.


“wo OG St uydap adig
“OL6L ‘725 ‘SuayIY UL YIdap WO Oz 2e UOLZeLUeA aunzevadue} LeNUUe pare{NULS

HINOW

“@L aunbly

if

pezesyuy

Buroeds adig wo gz

Buroeds adig wo OpL

rol

PS2

do - auNnzeuadwal

23


“w2 OG St Yyadaq adtd

“OL6L ‘840 ‘pueL{4od UL YIdap WO OL 72 UOLZeLUeA aunqeuadwaz [enuUyY paze{NWis “6 aunbLy
HLNOW
ON, OO, Sy, Ye, OW, VW, sie
tS

pazeoyul

Burseds adig wo Op

r Ol

r SL

[02

L G2

Jo - aunzeuaduial

20


10

11

12

13

14

LIST OF FIGURES (cont'd)

Page
Isotherms (°C) for a Pipe Spacing of 280 cm 14
and a Pipe Depth of 50 cm for Average Monthly
Weather Data and Condenser Discharge Temper-
ature (29°C) for Portland, OR. in January. The
Simulation is for 3] Days Operation.
Isotherms (°C) for a Pipe Spacing of 280 cm 18
and Pipe Depth of 50 cm for 72 Days of
Operation in Portland, OR. in January.
Simulated Annual Temperature Variation at 20
10 cm Depth in Portland, OR., 1970.
Simulated Annual Temperature Variation at 21
20 cm Depth in Portland, OR., 1970.
Simulated Annual Temperature Variation at 22
10 cm Depth in Athens, GA., 1970.
Simulated Annual Temperature Variation at 20 23
cm Depth in Athens, GA., 1970
Annual Temperature Variation at 10 cm Depth 24
in St. Paul, MN., 1970.
Annual Temperature Variation at 20 cm Depth 25

in St. Paul, MN., 1970.


LIST OF FIGURES

Comparison of Calculated Temperature (°C) With 6
Experimental Values From Sepaskhah (1974).

Comparison of Calculated Moisture Content 7
(cm?/cm?) With Experimental Values From
Sepaskhah (1974).

Temperature Distributions (°C) for Various 8
Irrigation Methods. The Simulations are for

Average August Weather Data From Portland, OR.

and for a Pipe Temperature of 41°C.

Mositure Content Distributions (cm? /cm?) for 9
Various Irrigation Methods. The Simulations

are for Average August Weather Data From Portland,
OR. and for a Pipe Temperature of 41°C.

Temperature and Moisture Content Distributions 12
for a Pipe Spacing of 140 cm and a Pipe Depth of

100 cm and Average Monthly Weather Data and
Condenser Discharge Temperature for Portland, OR.

in August. Simulation is for 31 Days of Operation.

Moisture Content Distribution for a Pipe Spacing 13
of 280 cm and a Pipe Depth of 50 cm for Average
Monthly Weather Data and Condenser Discharge
Temperature for Portland, OR. in January. The
Simulation is for 31 Days of Operation.

iv


SECTION IV
RESULTS

The model used in this research simulated irrigation provided at
the heating pipe. The soil warming system was simulated for 31 days
using January and August weather data and pipe temperatures starting with
temperature and moisture contents representative of an unheated soil.

The soil warming and irrigation system pipe spacings were 140, 280, and
560 cm while pipe depths of 50 and 100 cm were used. Typical computer
simulations are shown on Figures 5 through 7. The average increase of
soil temperature and moisture content in the soil profile from the
surface to a depth of 100 cm and the percent of this region with a
temperature of 24°C or higher were calculated. These quantities are
presented in Table 1. Table 2 shows the average increase in soil temper-
ature and the average increase in moisture content in the soil profile
to a depth of 200 cm and the percent of the 200 cm region with a temper-
ature of 24°C or higher. Since increased moisture content and temperature
represent more favorable conditions for plant growth, these quantities
are used to evaluate the relative benefits of the different pipe spacings
and depths.

It is observed from these simulations that the increase in water
content is greatest for the 50 cm pipe depth, that the 50 cm pipe depth
provides better soil warming for the 0 to 100 cm region and that the 100
cm pipe depth provides better soil warming for the 0 to 200 cm region.
Based on the increased moisture content and the fact that plants
have ultimate root depths considerably less than 200 cm in the early
half of the growing season, and that few plants or soils reach to 200
cm depth, the shallower pipe depth is deemed more beneficial.

1


SECTION I
INTRODUCTION

The use of soil warming systems in agriculture appears attractive
for several reasons. Plant growth rate is increased appreciably by
warming the soil to temperatures in the range of 20 to 32°C (Beall,
1973; Boersma, et al. 1974; Berry and Miller, 1974). Soil warming can
extend the growing season, increase the percent of seed germination and
provide frost protection. For example, tomatoes and cucumbers exhibit
increased growth and earlier ripening when grown in greenhouses main-
tained in the 25-30°C temperature range. Bush beans cultivated on a
plot with a soil warming system have been double-cropped where only one
crop was possible without the system (Boersma et al., 1974).

The potential of soil warming systems for frost protection is
limited to foliage near the ground and is probably of little value in
open fields. Berry and Miller (1974) reported that a greenhouse heated
only by a soil warming system maintained a temperature of 2°C (36°F) at
1 foot above ground, while the temperature 5 feet above the ground in
the greenhouse was -8°C (17°F) and the outside temperature was -21°C (-
5°F).

Soil warming has been accomplished by burying electrical cables in
the soil to provide heating. Although this method can provide arbitrary
heating rates to the soil, it is expensive to operate and consumes
electrical energy. Rykbost (1973) reported eneray consumption rates for
a demonstration plot of approximately 2000 to 6000 Kilowatt-hours/day
for 300 square meters. This power usage is equivalent to 8.0 x 10° -
2.4 x 10° kw/acre/mo. At a cost of 3¢/kw-hr., operating expenses would


Operation of the soil warming system over the entire growing season
would also result in higher temperatures than those based on 31 days of
operation. Figure 8 presents the results of a simulation for January
conditions for 72 days operation with pipe spacing of 280 cm and depth
of 50 cm. Comparison with Figure 7 illustrates the effect of prolonged
system operation, since the temperatures presented in Figure 8 are
appreciably higher than those of Figure 7.

Since installation is a major cost, the soil warming system should
be a permanent installation. Provision must, therefore, be made for
subsequent cultivation of the soil. Therefore, the soil warming pipes
should be buried deeper than the maximum cultivation depth. A pipe
depth of 30-50 cm (13-19 in.) is recommended to provide optimum irriga-
tion, allow for cultivation, and provide the maximum amount of soil
warming to the roots over the entire growing season.

From the data developed by the computer simulations, pipe spacings
of 140 cm appear adequate for open field operation in moderate climates.
The data presented in Tables 1 and 2 also indicate that decreasing the
pipe spacing increases the soil warming and irrigation effects of the
soil warming system.

While there are indications of the effect of the pipe spacing in
the results presented in Tables 1 and 2, no optimum pipe spacing can be
specified without performing a complex economic study of the benefits
derived from decreasing pipe spacing compared to the increased costs
caused by decreasing pipe spacing.

To further estimate the effects of the warming system for annual
operation, the computer simulation used average monthly weather data for

WV


ENVIRONMENTAS

PROTECTION
AGENCY
EPA-G00/3-76-026 DALLAS, TEXAS
March 1976 Ecological ResealfRA pies


SECTION ITI
THE SOIL WARMING SYSTEM

The soil warming system examined in this research applies to open
field operations and is composed of parallel pipes buried in the soil at
uniform spacing and depth. Since installation costs are high, it is
desirable to be able to predict the effects of the system to ensure that
the pipes are laid at appropriate depths and spacing. The mathematical
model used employs partial differential equations governing heat and
mass transfer in porous media. Axial variations along the pipe are
ignored, the soil is assumed to be saturated at a depth of 200 cm, and
the soil temperature is considered constant at a depth of 1350 cm.
Neglecting axial variations along the pipe introduces little error
because the flow rate of the condenser cooling water may be made high
enough to produce a small temperature drop along the pipe. The axial
temperature gradients would be much smaller than the radial gradients
and therefore negligible. The soil surface is treated as a plane with
no foliage. Radiant, convective, and evaporative heat transfer at the
surface is considered.

At the surface, the heat and mass fluxes are found by using weather
data along with empirical convection coefficients. The equations are
solved on a digital computer for the desired boundary conditions.

A laboratory experiment (Sepaskhah, 1974) was modeled to verify the
results of the computer simulation. The experimental apparatus consisted
of an insulated box of soil with a heat source and water source located
on one wall at a depth of 32 cm. The box was 48 cm high by 40 cm wide
and the particular soil modeled was a loamy sand. The temperatures


SECTION IT

CONCLUSIONS

Detailed design of a soil warming system would include the stated
considerations for a particular soil, climate, and crop. For the soil
and climates considered in this paper, the recommended design would
include the following suggestions:

1.

Use a pipe depth of 30-50 cm (13-19 in.)

Provide irrigation at the heating pipe.

To avoid corrosion problems, plastic pipe (polyurethane or
polyvinylchloride) is recommended.

A 1" diameter pipe appears most economical on the basis of the
cost analysis presented.

A pipe spacing of 140 cm or greater appears adequate for the
Portland, Oregon, climate while a 280 cm pipe spacing is
adequate for the Athens, Georgia climate. An extremely cold
climate similar to the 1970 St. Paul, Minnesota weather would
require pipe spacings less than 100 cm even though 140 cm pipe
spacing provided significant heating.


“w2 QG St Yyidap adig

“OL6L <°e9 ‘Suauiy UL YZdap WO OL 7e UOLZeLUeA auNqyeuaduia? LeNuUe pazeiNULS “LL aunBLy
HLNOW
rf ow eos yy yer ye wey if
r OL

pazeayun

Burseds adiq wo ogz

Burseds adiq wo OL

do - aunzeraduas

22


“wo Og St yrdap adid

“OLEL 61840 Spurl Og UL UZdap WO OZ 7 UOLZELAeA aunzevadwaz LenuUe pazeiNWLS “OL SunBLy
HLNOW
1O,N 4,0, Sy Vy Cy Py Wy, V~Wyd ye
FS
pazesyun fF OL

Buroeds adtd wo Opt

Jo - aunzevadwal

21


ABSTRACT

This work was performed to provide potential users of soil warming
systems with some general guidelines for the design of a soil warming
installation. Although a detailed design is not included, the general
configuration of such a system is discussed.

A computer program that solves the equations governing heat and
water transfer in soils was used to simulate the operation of a soil
warming system composed of a series of buried pipes at uniform spacing
and depth carrying warm water. The results include temperature and
moisture content distributions for various soil warming system pipe
spacings and depths and for varying weather conditions. Annual tempera-
ture cycles are presented for Portland, Oregon; Athens, Georgia; and St.
Paul Minnesota; for soil with no heating; and for soil with a contin-
uously operating soil warming system.

The conclusions include suggested soil warming system pipe spacing,

depth and size. Recommendations concerning irrigation methods are also
included.

vi


Depth from soil surface - cm

20 4

40 4

60 5

80 4

100 4

120 4

140 4

160 4

180 4

200 T T T T T T
0 20 40 60 80 100 120 140

Horizontal distance from pipe - cm

Figure 7. Isotherms (°C) for a pipe spacing of
280 cm and a pipe depth of 50 cm for average
monthly weather data and condenser discharge
temperature (29°C) for Portland, Ore. in January.
The simulation is for 31 days operation.


SECTION V
REFERENCES

Beall, S. E. 1973. Conceptual design of a food complex using
waste warm water for heating. Journal of Environmental
Quality. Vol. 2, No. 2.

Berry, James W. and Herman H. Miller, Jr. 1974. A Demonstration
of Thermal Water Utilization in Agriculture. U.S. Environmental
Protection Agency EPA-660/2-74-011. Corvallis, Oregon.

Boersma, L., L. R. Davis, G. M. Reistad, J. C. Ringle, and W. E.
Schmisseur. 1974. A Systems Analysis of the Economic Utiliza-
tion of Warm Water Discharge from Power Generating Stations.
Oregon State University Engineering Experiment Station Bull.
No. 48. Corvallis, Oregon.

Hanson, E. G., B. C. Williams, D. D. Fangmeier, and 0. C. Wilke.
1970. Influence of Subsurface Irrigation on Crop Yields and
Water Use. Proceedings of National Irrigation Symposium.
University of Nebraska, Lincoln, Nebraska.

Hanson, E. G., and B. C. Williams. 1968. Subsurface Irrigation of
Cotton. Proceedings of National Irrigation Drainage Speciality
Conference, Phoenix, Arizona, American Society of Civil Engineers.
p. 281-292.

Newman, J. S. 1965. Evaluation of Subirrigation of Crop Production.
Proceedings of West Texas Water Conference, 3:97-103.

29


7. Rykbost, K. A. 1973. An Evaluation of Soil Warming for Increased
Crop Production. PhD thesis. Oregon State University,
Corvallis, Oregon.

8. Sepaskhah, A. R. 1974. Experimental Analysis of Subsurface
Heating and Irrigation on the Temperature and Water Content of
Soils. PhD thesis. Oregon State University, Corvallis,
Oregon.

9. Zetzsche, J. B., Jr. 1964. Evaluation of Subirrigation with

Plastic Pipe. American Society of Agricultural Engineers.
Paper No. 64-731. St. Joseph, Michigan.

30




DISCLAIMER

This report has been reviewed by the Corvallis Environmental Research

Laboratory, U.S. Environmental Protection Agency, and approved for

publication. Mention of trade names or commercial products does not

constitute endorsement or recommendation for use.

ii


Depth from soil surface - cm

T T T
28 32 436 «4

Horizontal distance from pipe - cm

Figure 2. Comgarigon of calculated moisture content
(cm?/cm>) with experimental values from
Sepaskhah (1974).


“dol JO aunzevaduay
adid eB uoy pue “aug ‘puel quod UOJ eVep 4aYZRaM ysnBny abeuarae vo} aue suoLzeinuis
ay, “Spoyzau uolqeBLauL snoLueA sos (,u9/ ,u>) SUOLINGLAZSLP }UaZUOD BUNISLOW “py A4NBLY

adig Burqeay quajuo9
dy. 7 uoLzeH Lay UOLTeBLAAT voOLIeBiuuy  asaunqsLow
wo - adid wouj aouezsiq aoe,uns ON LBLQLUT
0£ 09 Ob o2 Oo
2 4 : Ope 7 OBER OOH 7 002
a
ley" 4 gly J 61° + O8L
a cob] 96E7 SET TOL
ly’ gee" 4 ve” 4 LE’ + Obl
3
ct
is
Le" 4 ose’ J 9g"  OZL 4
g
ge" 4 oze* 4 ize’ 7 00L Y
wn
ise" 4 982° 462° +08 §
Py
oO
oO
vee’ J 6vz" e92° +09,
Q
3
2ve" 4 Liz’ 4 blz’ + Ov
Ove’ + v6’ 4 L6L° + 02
ve"
ove: + too + 6vl° +0


EPA-600/3-76-026
March 1976

DESIGN GUIDELINES FOR AGRICULTURAL SOIL WARMING
SYSTEMS UTILIZING WASTE HEAT

by

David L. Slegel
Assessment and Criteria Development Division
Corvallis Environmental Research Laboratory
Corvallis, Oregon 97330

U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
CORVALLIS ENVIRONMENTAL RESEARCH LABORATORY
CORVALLIS, OREGON 97330


Based on a cost of 8.6¢, 12¢, and 35¢ /FT for 1/2", 1", and 2" PVC
pipe, respectively, a pumping efficiency of 50%, 5 years of pumping and
a cost of 3¢ /kw-hr, the costs of the piping and pumping for 100 meters
are:

"

Costs = Pipe Cost + (5) 365(24) (x) (qptqq) (.03)

$126.50 for 1/2"
= $ 43.10 for 1"
= $116.14 for 2"

Based on this simple cost analysis, the 1" diameter PVC pipe would
be chosen.

28


Depth from soil surface - cm

20 + 8

wy)

60 47 28

12
80 4
100 - 24
120 4
140 4

160 4

180 -

200 T T T T T T
0 20 40 60 80 100 120 140

Horizontal Distance from pipe - cm.

Figure 8. Isotherms (°C) for a pipe spacing of 280 cm
and pipe depth of 50 cm for 72 days of operation in
Portland, Ore. for January weather data.

18


RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:

1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research

4. Environmental Monitoring

5. Socioeconomic Environmental Studies

This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal
species, and materials. Problems are assessed for their long- and short-term
influences. Investigations include formation, transport, and pathway studies to
determine the fate of pollutants and their effects. This work provides the technical
basis for setting standards to minimize undesirable changes in living organisms
in the aquatic, terrestrial, and atmospheric environments.

This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.


“wd OG St yydap adig

“OLGL ‘“UULW * [Neg “3S UL UZdap WO QL Fe UOLZeLUeA aunjeuaduiaz [enUUy “Ee, eunBLy
HLNOW
ad, N,0, 5, ¥V,er,r,W,v,W, i,
pazeayun —— 0

Butoeds wo Ov

BuLoeds wo QOL

S 4
:
s
¢
3
f Ol 4
3
+ SL

[ 02

24


TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)

T REPORT NO. 2. 3, RECIPIENT'S ACCESSION NO.
EPA-600/3-76-026

a. TITLE AND SUBTITLE IS. REPORT DATE
DESIGN GUIDELINES FOR AGRICULTURAL SOIL WARMING March 1976

6. PERFORMING ORGANIZATION CODE

SYSTEMS UTILIZING WASTE HEAT

7, AUTHOR(S) 8. PERFORMING ORGANIZATION REPORT NO,

David L. Slegel

PE eens PE SBNGASE Ta HANA OBRENE Division a ea

Corvallis Environmental Research Laboratory
Office of Research and Development

i ion A
HS: af 2TOHRERER psspection Agency

T7. CONTRACT/GRANT NO.

12. SPONSORING AGENCY NAME AND ADDRESS 13. TYPE OF REPORT AND PERIOD COVERED
Interim
same 14, SPONSORING AGENCY CODE
EPA-ORD

15, SUPPLEMENTARY NOTES

16. ABSTRACT

This work was performed to provide potential users of soil warming systems with
some general guidelines for the design of a soil warming installation. Although
a detailed design is not included, the general configuration of such a system
is discussed.

A computer program that solves the equations governing heat and water transfer in
soils was used to simulate the operation of a soil warming system composed of a
series of buried pipes at uniform spacing and depth carrying warm water. The re-
sults included temperature and moistrue content distributions for various soil
warming system pipe spacings and depths and for varying weather conditions. Annual
temperature cycles are presented for Portland, Oregon; Athens, Georgia; and St.
Paul, Minnesota; for soil with no heating; and for soil with a continuously opera-
ting soil warming system.

The conclusions include suggested soil warming system pipe spacing, depth and
size. Recommendations concerning irrigation methods are also included.

KEY WORDS AND DOCUMENT ANALYSIS

*Beneficial use-industrial water, *Therma

DESCRIPTORS. Ib. IDENTIFIERS/OPEN ENDED TERMS fc, COSATI Field/Group

water, *Water Utilization, Heated water, Waste heat use in ag- OSF
Water Pollution Control, Thermal Pollutign, riculture, thermal
Agriculture, *Frost protection, Irrigatign pollution control,
water, *Soil-water-plant relationships, soil heating

Soil temperature

iS. DISTRIBUTION STATEMENT 19. SECURITY CLASS (This Report) 21. NO. OF PAGES
UNCLASSIFIED
RELEASE 10 PUBLIC 20, SECURITY CLASS (This page) 22. PRICE
UNCLASSIFIED

EPA Form 2220-1 (9-73) 31

4 US GOVEANMENT PRINTING OFFICE 1976~696-883170 REGION 10



1970 together with average monthly condenser discharge temperatures to
simulate operation for the entire year of 1970. Average monthly weather
data for 1970 were used and the condenser discharge temperature was
estimated by adding 22.2°C (40°F) to the calculated wet bulb temperature.
Figure 9 presents the average temperature at 10 cm depth for Portland
weather data for 1970 and for average predicted condenser discharge
temperatures for the Trojan nuclear power plant located near Portland.
Figure 10 shows the average temperature at the 20 cm depth for 1970
Portland operation. Pipe depth was 50 cm and the pipe spacing was 140
cm.

Simulations were also made for a warm climate, Athens, Georgia, and
for a cold climate, St. Paul, Minnesota. Figures 11 and 12 show the
annual temperature variations at the 10 and 20 cm depths for unheated
soil and for heated soil with a pipe depth of 50 cm and pipe spacings of
140 and 280 cm for the Athens climate. Figures 13 and 14 show annual
temperature variations for St. Paul.

An indication of benefits from operation of the soil warming system
can be obtained from Figures 9 through 14. As an example, Figure 9 may
be used to estimate the time by which the growing season could be
extended by use of soil warming systems. Without soil warming, a crop
with a seed germination temperature of 10°C could not be planted until
March. With soil warming, however, the required temperature is reached
approximately 15 weeks earlier at the 10 cm depth. Similarly, the late
growing season temperatures are extended appreciably.

SOIL WARMING PIPE SIZE

A typical heating rate was calculated from the results of the
computer simulation for 140 cm pipe spacing, 50 cm pipe depth and
January weather conditions. The heating rate, q, was:

19


and moisture contents were measured and are presented in Figures 1 and 2
for comparison with the results of the computer simulation. The experi-
mental and simulated results are in fair agreement and the computer
simulation is assumed valid for these conditions.

Irrigation of the soil subjected to soil warming is desirable, if
not necessary. Without irrigation, the soil dries and therefore is less
suitable for raising crops. The soil warming is also inhibited by low
moisture content since the thermal conductivity of soil decreases with
decreasing moisture content. Figure 3 presents temperature distribu-
tions after 31 days of simulated operation for a loamy sandy soil for 1)
soil warming with no irrigation, 2) irrigation at the heating pipe, and
3) surface irrigation. The irrigation rates were 10.8 cm/day (4.25
in/day), while the pipe depth was 50 cm and the spacing was 140 cm.

Both the unirrigated and the surface irrigated simulations indicate less
warming of the soil than does the soil warming simulation with irriga-
tion at the pipes.

Figure 4 presents the moisture content distributions for the cases
presented in Figure 3. The initial moisture content is a function of
depth only and is presented as point values versus depth. The moisture
content for the surface irrigated simulation and the simulation for no
irrigation varied only slightly in the horizontal direction. The
moisture contents for these two cases are therefore presented as average
values at the various depths. For example, the moisture content at 60
cm depth was 0.263 em? /em? initially, and after 31 days of operation was
0.249 cm?/cem® for no irrigation, 0.344 cm?/cm? for surface irrigation
and ranged from 0.42 to 0.38 em? /em? for subsurface irrigation. It is
noted that the unirrigated example is drier than the initial distribu-
tion and that the surface irrigated example is drier than the one with


“Joly JO aunqeuaduia} adid e uo} pue auQ ‘puelz4Og YO ePeP 4ayzZeOM ysniny abeuaar soy
Bue SUOLIE[NWLS aU] “SPOYPSW UOLZeHLUAL SNOLUPA UOJ (J,) SUOLINGLAZSIP aunqesaduia, “E e4nbLy

uoLzebiasy aoeyuns adid ay} 7e uoLzebLsuy uoLzebiuy ON
wo - adiq Bulzeay ay. wouy BduRZSIGg | e}PUOZLAOY “dua
09 4 02 0 04 09 op 0¢ 0 02 09 Ov 02 0 LeLztuy
7 * * LLL 7-002
02 y
“02
. 9°LL + O8L
22
. Let O9L
ce S74
“02 SSL 7 OVE
“92
“v2 | esl + OZL
L°6L + OOL
p6l 7 08
L6L + 09
6°61 + Ob
Loz + 02
voz 0

wo - adBJuns [LOS woud yydaq