PIH-102 HOUSING
PURDUE UNIVERSITY. COOPERATIVE EXTENSION SERVICE.
WEST LAFAYETTE, INDIANA
Earth Tempering of Ventilation Air
Authors:
Warren D. Goetsch, University of Illinois
Larry Jacobson, University of Minnesota
Randall Reeder, Ohio State University
Dennis Stombaugh, Ohio State University
Reviewers:
Eldridge Collins, Jr., Virginia Polytechnic
Institute and State University
Dexter Johnson, North Dakota State University
Richard Phillips, Pennsylvania State University
Harold and Dean Rogers, Petersburg, Illinois
David Shelton, University of Nebraska
Earth tempering of ventilation air for swine buildings is
being considered by many producers because of the moderate fluc-
tuations in soil temperatures at shallow depths. Depending on the
season, incoming ventilation air is heated or cooled as it passes
through a buried tube. The soil serves as a heat sink in the sum-
mer and as a heat source in the winter, thus giving almost year-
round temperature modification. It has the potential to signifi-
cantly reduce heating costs during winter and provide zone cool-
ing during summer.
Soil Temperature
Soil temperature is one of the most important factors
affecting design and performance of earth-tube heat exchanger
systems. Soil temperatures vary with soil type, depth, moisture
content, time of year, and geographic location.
The mean annual ground temperatures for various locations in
the United States are given in Figure 1.* In the central U.S.,
these mean annual ground temperatures range from 49o F. in St.
Paul, Minnesota, to 58o F. in Lexington, Kentucky, and from 52o F.
_____
* The drawings in Figures 1, 2, and 3 first appeared in ``Under-
ground Building Climate'' by Kenneth Labs, in the October 1979
issue of Solar Age, c 1979 SolarVision, Inc., Harrisville, NH
03450. All rights reserved. Reprinted and published by permis-
sion.
in Ames, Iowa to 55o F. in Columbus, Ohio. The variation of
ground temperature from this yearly mean at any site is suggested
by Figure 2. The amount of temperature variation decreases as
depth increases. For example, at a depth of 6 ft., the yearly
variation of a typical clay soil can be expected to range from 11
degrees above to 11 below the mean annual ground temperature, or
a total yearly variation of approximately 22 degrees. At a depth
of 10 ft., this variation is reduced to plus or minus 6 degrees
F. or a total variation of 12 degrees.
The time of year when the ground temperature is at the
extreme is also important in the design and performance of a sys-
tem. Soil temperature fluctuations lag behind surface temperature
changes due to the heat storage capacity of the soil. The soil
surface reaches maximum temperature during the heat of the sum-
mer, but soil 10-12 ft. deep may not reach its peak temperature
until almost three months later. This thermal lag at the 10 ft.
depth (Fig. 3) helps both the heating and cooling performance of
these systems. During the winter, soil temperatures at this depth
are at the fall season level, making the soil near the mean
annual ground temperature, thus adding to the heating capabili-
ties of a system. The reverse is true during the summer months,
when the soil temperatures at the 10-12 ft. depth are springlike
and can cool the ventilation air.
Soil types and moisture content also affect the ground tem-
perature variation. Soils with increasing sand content tend to
have larger temperature variations at deeper depths than clay
soils. Soil moisture and ground water elevation also affect soil
temperature. Seasonal temperature variation is larger in very
moist soils as compared to very dry ones due to the increase in
heat transfer through soils whose voids are filled with water.
System Design
The typical earth-tube tempering or heat exchanger system
consists of a heat exchanger field, a collection duct/fan house,
and a building air distribution system. Each of these portions
must be adequately sized to insure proper performance. The fol-
lowing sections may help to explain the many tradeoffs in system
design.
Airflow Capacity. In general, much more air is required for
summer ventilation than for winter. If zone cooling is used, the
difference between the two rates is much less (Table 1). For
example, the recommended summer zone cooling rate for a sow and
litter is 70 cu. ft. per minute (cfm) of uncooled air per farrow-
ing crate, 50 cfm for evaporative cooled air, and 30 cfm for
air-conditioned air. Air tempered by an earth-tube system should
be somewhat cooler and dryer than evaporative cooled air (depend-
ing on climate), but for planning purposes use the 50 cfm per
crate. During winter, the recommended cold weather ventilation
rate is 20 cfm per crate. With the system designed for a capacity
of 50 cfm per crate, there is an additional 30 cfm which can be
used for mild weather room tempering as needed or it can be used
to preheat the winter air of a compatible nearby nursery. Similar
design capacity figures are shown for gestation sows, boars, and
growing and finishing pigs in Table 1.
Comparison of the air volume requirements for a farrowing
house with and without the use of an earth-tube heat exchanger
system is shown in Table 2. A properly designed and managed sys-
tem allows the producer to reduce whole building ventilation rate
by one-half during the summer (50 cfm/crate of earth zone cooled
air plus 200 cfm/crate outside air versus the normal 500
cfm/crate outside air recommendation). If zone cooling is not
desired or possible because of interior room design, whole-room
cooling may be an option. For whole- room-cooling planning pur-
poses use an air volume of 100 cfm per farrowing crate or twice
the normal zone cooling rate. Adequate building insulation levels
and proper room air distribution systems are extremely important
to ensure successful ventilation with this type of system (See
PIH-65, Insulation for Swine Housing, and PIH 87, Cooling Swine).
Zone cooling is recommended over whole-room cooling because it is
more cost effective, especially in the farrowing and gestation
units.
Heat Exchanger Field Design. Both soil characteristics and
tubing factors affect the design and performance of a system.
Soil characteristics include soil type, moisture content, and
water table elevation. Temperature levels for various soil types
indicate the less favorable performance of sandy soils; so avoid
these if possible. If sandy soils must be used, the number of
lines, line lengths, and/or depth should be increased by 10 to
20% to offset this effect. Moisture content increases the heat-
transfer capability of the system. Therefore, a system installed
in an area with a shallow water table should have the lines
buried below the average yearly elevation of the water table for
maximum performance. Such a system must be well sealed to mini-
mize ground water seepage and additional pumping costs. Construc-
tion should take place during periods of low water table to
reduce the use of pumps and possibly unstable trench sides and
bottom.
Air-tubing factors include diameter, length, depth of place-
ment, and shape of the tube. Typically, nonperforated corrugated
plastic drainage tubing is used because of its availability and
cost. The recommended airflow rates for various tubing diameters
are shown in Table 3. These airflows are based on an air velocity
in the tube of 500-600 ft. per minute (fpm). Divide the total
airflow needed for the system by the recommended flow rate per
tube to indicate the number of tubes needed for a given system.
Table 3 also shows the recommended tubing length for various
diameters of tubing. This length is based on an air contact
(heat-exchange surface) of 1.3-2.0 sq. ft. of tube surface per
cfm of airflow (figures are based on smooth pipe for simplicity
of calculation). Small diameter tubing, such as the 3-, 4-, or
5-in. sizes, are impractical because of the large number of lines
needed to provide enough air capacity for a typical system; thus
the 8-, 10-, and 12-in. diameters are the most practical.
Layout. Several system layouts are possible, including the
wagon wheel (radial) or the lateral (see Figs. 4 and 5). Material
and trenching costs are normally less for the wagon wheel pattern
because no manifold lines are used; however, excavation can be
difficult near the collection duct. Manifold lines must be much
larger than lateral lines, and tubing materials and trenching are
more expensive. However, a lateral system with a manifold may be
the only option when surrounding buildings, roads, or fields
limit the area available for installing the system. The spacing
between lateral lines need not be uniform, but each lateral
should be of equal length to keep the airflow equal. Laterals do
not need to run straight, but abrupt turns should be avoided.
Placement. The tubing should be buried to a depth of 7-12
ft. depending on installation costs and geographic location. Sys-
tem thermal performance will be better with maximum depth. If
installation costs are prohibitive, somewhat shallower depths may
provide a more beneficial economic return.
Space lines at least 8-10 ft. apart to maximize soil heat
storage and minimize the chance of tubing deflection and damage
during construction. Trenches with multiple tubes and closer
tube spacings may be used to reduce construction costs; however,
line length should be increased to maintain adequate soil mass
for heat transfer. For example, four 6-in. diameter tubes have
about the same airflow capacity as one 12-in. diameter tube. If
four 6-in. lines are installed in a single trench, their length
should be the same as the 12-in. recommendation of 200-250 ft.
instead of the normal 6-in. tube recommendation of 100-130 ft.
Slope lines at a minimum of 2-3 in. per 100 ft. to a U-trap and
gravity drainage line at the outer tube ends or to a drain sump
at the collection duct. Constant slope is critical because any
low spots in the lines could fill with water and restrict air
flow.
Tubing should be installed carefully, in accordance with
ASTM Standard Designation: F 449-76.- Either trenchers or back-
hoes can be used for excavation, but hand blinding (careful
placement of select material over and on the sides of the tubing)
and narrow trenches with rounded bottoms should be used to ensure
constant slope and minimal tube deflection and damage. Modern
trenchers are equipped with laser plane-grade guides that ensure
a constant slope. However, most trenchers are restricted to
depths of less than 7 ft. unless a special adapter is available,
and 2-3 ft. of topsoil may need to be removed before trenching if
trenchers are to be used (Fig. 6). Backhoes are more expensive
but are available for depths down to 12 ft. and can, with care,
maintain a constant slope (Fig. 7). They can be used when trench-
ers are not practical; however, due to the extreme depths and
possible cave-in problems, trench sides should be sloped and
bulkheads may be needed to ensure a safe working area. Minimum
trench width should be 6 in. wider than the outside diameter of
the tubing. If extremely wide trenches are used, the tubing
should be placed in the corner of the trench against a trench
wall.
At the outer end of the system, the tubes should curve up
and extend 3 to 4 ft. above the soil surface to form the air
inlet. Either rigid PVC pipe or corrugated plastic tubing can be
used for the inlet risers; however, the tops should be screened
to keep out debris and rodents and should be very visible to
prevent damage from nearby machine traffic.
Collection Duct/Fan House Design. Common materials for col-
lection ducts below grade include reinforced concrete, concrete
blocks, and round steel. An example of one such reinforced con-
crete collection duct is shown in Figure 8. Size is determined
by system airflow and wall area requirements to make the tubing
connections. In general, collection ducts should provide enough
wall area to connect the lines and enough cross-sectional area to
keep airflow velocities below 500 fpm. Above grade, insulated
wood construction is acceptable to enclose the airstream. A prop-
erly sized fan must be installed at the connection between the
underground system (collection duct) and the building air distri-
bution ducts. Determine the size of the above-grade duct by the
size of fan to be enclosed and the type of service access
entrance to be used. Normally, the above-ground portion can be
constructed to the same dimensions as the below-grade portion and
still provide enough area for fan installation, access, and
maintenance.
Insulate the entire collection duct/fan house to at least
R-19 to a depth of 6 ft. below grade with moisture-proof insula-
tion. A closed cell polystyrene or polyurethane insulation is
recommended. A reverse tempering effect has been noted on instal-
lations in Illinois where no insulation was used below the 3 ft.
depth. In one case, air that had been cooled in the tubes was
reheated 5 degrees as it passed through the duct/fan house into
the building.
A fan should be located between the underground tubing sys-
tem and the building air distribution system. Size this fan to
deliver the desired airflows against to 1/2-in. static pressure.
Usually, a two-speed fan would be best, with the maximum volume
matched to the summer zone cooling rate and the smaller volume
matched to the winter continuous ventilation rate. Tightly seal
the collection duct and all connections to prevent short circuit-
ing of air from outside directly into the duct, thus bypassing
the tubing system.
Building Air Distribution System. The distribution system
for the earth-tempered air consists of a fan, main duct or ducts,
and downspouts (or drop ducts) located as needed for each animal
(Figs. 9 and 10). In a farrowing house, locate a downspout above
each individual crate with the airstream directed at the sow's
head. The downspout should be located as close to the animal's
head as possible to make full use of the cooled air. If spouts
are within the animals' reach, they should be made pig-proof.
Include dampers in the downspouts to close individual lines when
crates are empty and to adjust airflow if needed.
Main duct and downspout dimensions are given in Table 4.
These are minimum duct dimensions and should be increased if duct
framing is located inside the airstream. Insulate ducts to at
least R-6 to prevent heat gain and condensation during summer
operation.
For winter operation, earth-tempered air can be routed
through an existing room air distribution system, through room
make-up air heaters, or the summer downspouts can be removed and
tempered air can be introduced into rooms via the distribution
duct openings along the room ceiling.
Design Example
Design an earth-tube heat exchanger for a 24-sow farrowing
house. The summer zone-cooling ventilation rate equals 50 cfm per
sow and litter, and the continuous winter rate is 20 cfm per sow
and litter (Table 1). Therefore, the maximum airflow for the sys-
tem (zone cooling) equals 1,200 cfm (50 cfm per sow x 24 sows),
and minimum airflow equals 480 cfm (20 cfm per sow x 24 sows).
During the winter, the extra 720 cfm capacity of the system could
be used to heat and ventilate an adjoining nursery.
From Table 3, find that 6-in. tubing can carry 110 cfm per
tube. Eleven 6-in. tubes are required (1,200 cfm divided by 110
cfm per tube). For 8-in. lines, use six tubes (1,200 cfm divided
by 200 cfm per tube). For 10-in. tubing use four tubes (1,200
cfm divided by 300 cfm per tube). The suggested length for each
tubing size is given in Table 3. A system using eleven 6-in.
tubes, each 100-130 ft. long (depending on soil type); six 8-in.
tubes, each 130-170 ft. long; or four 10-in. tubes, each 160-210
ft. long, would be satisfactory. Check the cost of trenching and
materials in the area to determine which system would be most
economical. The relative costs of different tubing sizes are also
shown in Table 3. As the size of the tubing increases, the cost
of the material goes up. The material cost increases are espe-
cially large if tubing of 10-in. diameter or more is used.
Manifold lines, when used, must carry the entire flow that
goes through them at an appropriate velocity (refer to Table 3
for size). If six lateral lines of 8-in. tubing are installed, as
arranged in Figure 5, the manifold running in each direction to
the first lines needs to be 15 in. in diameter (200 cfm per 8-in.
line x 3 lines = 600 cfm). The manifold can then be decreased to
a 12-in. size to the second lines (200 cfm per 8-in. line x 2
lines = 400 cfm). After the second line is connected, the mani-
fold can be reduced to an 8-in. diameter tube out to the last
line. The vertical tube coming out of the ground should be a 24-
in. tube or larger.
Size the fan to supply 1,200 cfm at the high setting and 480
cfm at the low setting while working against to 1/2 in. of
static pressure.
From Table 4, an 18- by 18-in. or 10- by 30-in. (inside
dimensions) main duct will carry the 1,200 cfm airflow. If crate
layout is such that two ducts are needed, two 12- by 12-in. or
two 6- by 24-in. ducts could also be used. Also from Table 4, a
4-in. diameter downspout or a 3- by 3-in. square downspout would
carry the desired 50 cfm per crate airflow to each animal.
System Costs
Major costs encountered when installing an earth-tube heat
exchanger system include: excavation, tubing, fan, and the inte-
rior distribution system. Cost will vary with the depth of ins-
tallation, excavation method, layout, and site constraints.
Obtain cost estimates for the specific site, layout, and desired
depth before selecting a final design. Figure 11 shows a typical
breakdown between trenching and tubing costs for tubing of dif-
ferent diameters in a system delivering 2,000 cfm of air
installed at an average depth of 9 ft. For a 2,000 cfm system,
the 8-, 10-, and 12-in. tubing sizes were the most economical in
this case. The figure also indicates average tubing and excavat-
ing costs are approximately $2 per cfm of air capacity. Fan and
distribution system costs usually average approximately 50 cents
to $1 per cfm of air capacity. Thus, total costs for an average
system should range from $2.50 to $3 per cfm of system air capa-
city (1985 costs).
Performance Data
Several functioning systems have been monitored in Illinois
during the past few years, including systems designed according
to the guidelines presented here. Summer and winter performance
curves for a 30-crate farrowing facility located near Spring-
field, Illinois, are shown in Figures 12 and 13. The system con-
sists of five 12-in. lines, each 260 ft. long, buried about 10
ft. deep.
The outside temperature for a three-day period in August
1981 (Fig. 12) varied from 60 to 92o F. The earth-tempered air
temperatures ranged from 64 to 69o F. The average sensible cooling
effect during the three-day period was equivalent to 20,773
Btu/hr. The temperature of the outside air during the three-day
period in January 1982 (Fig. 13) varied from +20 to -19o F.,
whereas the earth-tube output temperature was steady at 46 to
48o F., a maximum temperature increase of 67 degrees. The earth-
tube heat exchanger provided about 40% of the heating required
during the winter of 1981-82 by delivering tempered air at the
approximate rate of 920 cfm.
Economic Payback
As with other alternative energy systems (solar and heat
exchangers), tempering of ventilation air by earth-tubes is not
free. Since the costs and returns vary considerably for earth-
tube systems, a rigorous economic analysis would be both diffi-
cult and lengthy. However, to give some indication of economic
payback for a system, the following example is provided, using
the performance data and costs given above, plus estimated
returns and expenses.
Figure 13 gives the ``heating'' performance of a system over
three days in January from a 30-crate farrowing barn in Illinois.
A relatively constant exhaust air temperature from the earth-
tubes of 48o F. was recorded over this period. If one assumes this
same temperature over the entire heating season (will probably be
greater in the fall and less toward spring), then the amount of
energy recovered per heating month can be found using the follow-
ing relationship:
Q = 1.1 x 920 cfm x (To -T) x 24 x (number of days in month)
where
Q = Btu/month
To = temperature exiting tubing (48o F. for our example)
T = average monthly outside temperature Using average
monthly temperatures for central Illinois during the heating sea-
son (November through March), a total of 61.5 million Btu's of
energy would be recovered. If this total is divided by 75,000
Btu's (amount of usable energy per gallon of L.PP. gas) then this
is the energy contained in 820 gal. of propane. At 75 cents per
gallon, a total of $615 would be saved per year. Since a larger
fan (1/2 h.p.) is needed in this system than with conventional
ventilation, a total of $100 (2,000 kwh x 5 cents/kwh) should be
subtracted from $615 for a net return of approximately $500 per
year from heating.
Estimating the cooling benefits during the summer is much
more difficult than calculating heat savings. It would be unfair
not to consider the returns from cooling, especially when compar-
ing the earth-tube system with solar units and air-to-air heat
exchangers. Some animal scientists have estimated that 1 extra
pig per litter occurs if a summer cooling system is used, because
of reduced sow heat stress, more efficient sow milk production,
and faster breeding. If that assumption is used in our example,
then 30 extra pigs per farrowing would result for a total of 60
extra pigs (assume 2 farrowings per summer). If an estimated
value of $15/extra pig is assumed, this results in a return of
$900 due to cooling. Adding this amount to the annual estimated
heat savings ($500), a total return of $1,400 per year results.
The costs of the above 1,500 cfm earth-tube system is
estimated at $4,500, when using the $3/cfm figure discussed ear-
lier (1,500 cfm x $3/cfm). The simple payback period, which
excludes fuel price increases and interest, would be between
three and four years. Consideration of L.PP. gas (propane) price
increases would reduce paybacks while the inclusion of high
interest rates would extend them considerably.
As is apparent from the above example, the economic feasi-
bility of an earth-tube system should be thoroughly investigated
before beginning construction. While the heat savings can be cal-
culated accurately, one should also give adequate weight (or
value) to the estimated cooling benefits. Solar systems and heat
exchangers provide no summer cooling while mechanical air condi-
tioning has proved to be too costly. Earth tempering of ventila-
tion air may be the least-cost alternative for providing tempered
air during all times of the year.
NEW 5/85
Table 1. Recommended ventilation rates for swine in environ-
mentally regulated buildings.
_______________________________________________________________________________
Hot weather
_____________________________________________
Zone cooling
_____________________________________
Swine Cold Mild Uncooled Evaporative Air-condi-
type weather weather air cooled air tioned air Normal
_______________________________________________________________________________
cfm per head
________________________________________________________________
Sow and litter 20 80 70 50 30 500
Prenursery
(12-0 lb) 2 10 - - - 25
Nursery
(30-75 b) 3 15 - - - 35
Growing
(75-150lb) 7 24 - - - 75
Finishing
(150-20 lb) 10 35 - - - 120
Gestation sow
(25 lb) 12 40 45 30 20 150*
Boar
(400 lb) 1 50 60 40 20 180
_______________________________________________________________________________
* 300 cfm for gestating sows or boars in a breeding facility
due to low animal density.
Table 2. Ventilation comparison between a farrowing
house with and without an earth-tube heat exchanger
system.
_______________________________________________________
Ventilation rate requirement
_________________________________________
Ventilation Normal building Building with
rate type* without earth system* earth system
_______________________________________________________
Cold weather 20 cfm/crate 20 cfm/crate
(outside air) (earth-tempered
outside air)
Mild weather 80 cfm/crate 50 cfm/crate
(outside air) (earth-tempered
outside air)
Hot weather 500 cfm/crate 250 cfm/crate
(outside air) (50 cfm/crate
earth-tempered
plus 200 cfm/
crate outside
air)
_______________________________________________________
* Same as Table 1.
Table 3.Earth-tube heat exchanger line dimensions and capacities.
_________________________________________________________________
Suggested Suggested
Tube Nominal tube Relative line airflow
diameter area cost per lengths per tube
(in.) (sq. in.) ft.* (ft.)** (cfm)***
_________________________________________________________________
4 12.6 $0.25 65 -- 85 50
5 19.6 0.35 80 -- 105 80
6 28.3 0.55 100 -- 130 110
8 50.3 0.90 130 -- 170 200
10 78.5 1.85 160 -- 210 300
12 113.1 2.30 200 -- 250 450
15 176.7 3.80 250 -- 320 700
18 254.5 6.30 300 -- 380 1000
24 452.4 14.40 400 -- 500 1800
_________________________________________________________________
* Costs vary with different manufacturers and change over
time. These costs are only offered to give a relative figure
for different sizes of tube.
** Line length ranges indicate the effect of soil type and
moisture content on line dimensions. The low end of the range
corresponds to a wet clay soil type and is based on 1.3 sq.
ft. of tube surface area per cfm of airflow. The high end of
the range corresponds to a dry sand soil condition and is
based on 2.0 sq. ft. of tube surface area per cfm of airflow.
All surface area calculations were made assuming smooth pipe
for simplicity.
*** These airflow rates allow for a air velocity of 500 to 600
fpm.
Table 4.Building air distribution main duct and downspout
dimensions. Main duct sizes are based on duct air velocity of
600 fpm. Downspout sizes are based on air velocities of 800-
1,000 fpm.*
____________________________________________________________
Inside duct dimensions if:
___________________________
Air flow rate
within duct Rectangular Round
____________________________________________________________
cu. ft./min. in. x in. in. diam.
Main duct sizes 250 6 x 10 9
500 10 x 12 12
750 10 x 18 15
1000 12 x 20 18
1250 15 x 20
1500 18 x 20
2000 18 x 27
2500 18 x 34
3000 18 x 40
3500 24 x 35
4000 24 x 40
5000 24 x 50
6000 30 x 48
7000 36 x 48
8000 36 x 54
Downspout sizes 20 2 x 2 21/2
30 2 x 3 21/2
40 21/2 x 3 3
50 3 x 3 31/2
75 3 x 41/2 4
100 4 x 41/2 5
125 4 x 51/2
150 4 x 61/2 6
175 4 x 8
200 6 x 6
250 6 x 71/2 8
____________________________________________________________
* It is the minimum cross-section area, not the actual
duct dimensions given in the table, that is important. Almost
any duct shape of comparable size should deliver the same
amount of air.
Figure 1. Well-water isotherms indicating the mean annual ground temperatures
for the 48 contiguous states.
Figure 2. Yearly variation of soil temperature with relation to depth below
surface for average soil.
Figure 3. Annual ground temperature curves at the soil surface, at a depth of
10 ft., and the annual mean for generalized conditions at
Lexington, Kentucky, showing the degree of thermal lag at the 10-ft.
depth.
Figure 4. System layout using the wagon wheel or radial pattern.
Figure 5. System layout using the lateral tubing pattern.
Figure 6. Chain-trencher excavating and installing 12-in. diameter tubing
for a 1,600-cfm capacity system in Menard County, Illinois. Three
to 4 ft. of soil was removed, using a bulldozer before the trencher
was used to install the tubing an additional 6 ft. into the soil.
Figure 7. Backhoe excavating and installing 12-in. diameter tubing
to a depth of 12 ft. for a 2,000-cfm capacity system in Sangamon
County, Illinois. For safety reasons, the trench walls run up
vertically only 6 ft. and the upper 6 ft. is set back to reduce
cave-in problems. The evaporative cooler on the building roof is
being replaced by the earth-tube heat exchanger system.
Figure 8. Reinforced concrete collection sump on a 4,000-cfm capacity system
in Peoria County, Illinois. At the sump, the tubing lines are
approximately 8 ft. below grade but slope away from the building
where they become 10-12 ft. deep. A portion of the sump was chipped
out after the producer decided to increase the number of lines in
the system.
Figure 9. Tempered air to this 24-crate farrowing facility in Shelby County,
Illinois, is carried down the center of the building via the insulated
main duct shown. Downspouts are 4-in. diameter PVC pipe with flexible
dryer hose used to allow opening and closing of crate doors.
Figure 10. Downspouts can be used to bring the tempered air down into the
crate a few inches away from the sow. Here PVC tubing has been used
to direct the air through the crate door directly on the
animal's snout.
Figure 11. Tubing and trenching costs for a typical 2,000-cfm capacity system.
______________________________________________
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