HOUSING                                           PIH-87


                            Cooling Swine

Don D. Jones, Purdue University
L. Bynum Driggers, North Carolina State University
Robert L. Fehr, University of Kentucky

Gerald Gehlbach, Lincoln, Illinois
Albert J. Heber, Kansas State University
Howard Person, Michigan State University
Russell and Janet Roberson, Devina, Texas

     Hot  weather  reduces  swine  performance  more  than   cold
weather,  resulting in significant economic loss to the pork pro-
ducer. This occurs because buildings in much of the United States
are  designed  for cold weather while producers often are content
to ``wait out'' hot spells. Hot weather usually does  not  result
in  death losses, but it can cause conception problems and subtle
reductions in feed intake that result  in  significant  drops  in
production.   Reduced  sow  feed  intake also can affect baby pig

     The purpose of this  publication  is  to  suggest  practices
which minimize animal production losses through the use of effec-
tive, energy-efficient cooling systems. Discussed first  are  the
ways in which pigs give off excess body heat. This is followed by
a discussion of the various types of  cooling  systems  based  on
heat dissipation principles. The information provides a basis for
evaluating your present system or selecting one  that  best  fits
your situation.

Heat Dissipation

     Larger pigs (animals in gestation, farrowing,  breeding  and
finishing phases of production) begin to feel the effects of heat
stress at about 70o F. If temperatures remain above 85o F for  more
than  a  short  period of time, substantial losses in performance
and in reproductive efficiency can result  unless  some  type  of
cooling  relief  is  provided.  Pigs  dissipate  little  moisture
through their skin-certainly not  enough  to  rid  themselves  of
excess  body  heat.  Therefore, to relieve heat stress, they must
depend upon heat dissipation to their environment in one or  more
of  the  following  ways:   convection, conduction, radiation, or
evaporation through the respiratory tract (panting).  Evaporative
cooling  from  the  body surface also is possible if some type of
artificial surface wetting is provided along  with  adequate  air
movement over the animals.


     Convection heat loss results  from  air  movement  over  the
animal's  body.  This  is an effective means of cooling, provided
two conditions are met: (1) the air velocity is at least  2  mph,
and  (2)  the  air  temperature  remains  at least 10o F below the
animal's body temperature (102 _ 1o F). At air temperatures in the
range of 80o F to 95o F, pigs can dissipate up to 30% of their body
heat by convection to the surrounding air.


     Conduction heat loss occurs when the  animal's  skin  is  in
direct contact with a cooler surface. Conduction usually accounts
for only 5% to 10% of the total heat loss in hot weather, because
temperature  differences  are  small  and  only  about 20% of the
animal's skin is in contact with the floor surface, even less  if
the floor is slotted.

     Conductive heat loss to the  cool  ground  surface  under  a
shade  in  a  pasture or a lot can be significant. However, it is
not as important in concrete-floored  buildings,  because  higher
building insulation levels and a greater concentration of animals
maintain a warmer floor surface temperature.   Insulation  placed
under  the  floor or along the foundation specifically to control
winter heat loss further reduces summer conductive cooling.


     The surface of an animal's skin is constantly radiating heat
to  or  receiving  radiant  heat from its surroundings. Where the
surrounding wall, ceiling and floor surfaces are cooler than  the
skin, there will be a net loss of heat from the animal, making it
feel cooler. Radiant heat loss is directly related to the insula-
tion level of the building. Insulation keeps inside building sur-
faces cool in the summer, especially the roof or ceiling.  Radia-
tion  typically  accounts  for about 20% of the total animal heat
loss in the summer, but  if  building  surface  temperatures  are
above  that  of  the animal, there will be a net heat gain by the


     Evaporative heat loss from the animal's breathing process is
important,  particularly at high temperatures. For every pound of
water evaporated, about 1,000 Btu of heat is required.  At  80o F,
panting  accounts  for  nearly 40% of the total heat loss. Conse-
quently, in providing relief from hot weather, it is important to
keep  the  air around the animal's head as cool and dry as possi-
ble.  This is the basic premise behind the concept of snout cool-
ing of sows and wet skin cooling systems.

Shade Cooling

     The use of sun shades in pastures and  outside  lots  is  an
effective  method  for  helping  livestock  keep cool (Figure 1).
Shades can cut the radiant heat load from the sun by as  much  as
40%.  They work by blocking out the sun's direct rays and provid-
ing a cooler ground surface on which the animals can lie.

     Shades should have their long axis oriented in an  east-west
direction.  High  shade height maximizes the animal's exposure to
the ``cool'' northern sky, which will help maximize radiant  heat
loss from the animal.

     From a cooling standpoint, shades with straw roofs are  best
because  they supply a high insulation value as well as a reflec-
tive surface. However, uninsulated aluminum or bright  galvanized
steel  roofs also are effective. Painting the upper surface white
(or with a reflective paint) and the lower surface black improves
cooling   by   about  10%.  Wood  snow-fencing,  a  common  shade
material, is about half as effective as straw or  painted  metal.
Greenhouse  shade cloth works well and is reasonably durable when
exposed to the sun and wind.

     Shades are most effective if they are placed on high  ground
where  they can catch the summer breezes. Lightweight shades must
be well-anchored to prevent overturning in strong winds. Locating
them  at least 150 ft downwind from a wooded area or lush vegeta-
tion helps cool the breeze.

Adequate Insulation

     In enclosed buildings, insulation in the roof or ceiling  is
essential  to  minimize  solar  heat  buildup in hot weather. See
PIH-65, Insulation for Swine Housing for detailed information  on
insulation for swine buildings.

     Sidewall insulation is not significantly beneficial for sum-
mer  cooling  if  the  building is oriented east-west because the
summer sun passes almost directly overhead during the heat of the
day.   A  north-south oriented building, however, should have the
sidewalls as well as the roof or ceiling insulated because of the
high  solar  heat load on the sidewalls. Sidewall insulation also
will be needed to control winter heat loss in most  climates  and
in buildings which use evaporative or refrigeration-type cooling.

     In north-south oriented naturally ventilated buildings  with
large  sidewall  openings, horizontal sun screen may be needed on
the west to block the afternoon sun. This should  not  block  the
flow  of  cross  building  ventilation air. The attic area over a
building with a ceiling should be well ventilated to prevent heat
buildup and subsequent radiation of heat to the animals.  Provide
at least 1 sq ft of ridge and eave vent opening to the attic  for
each 300 sq ft of floor area.

Ventilation Cooling Systems

     Rapid air movement over the animal aids in  both  convective
and  evaporative  heat  loss.  An  air  velocity below 1/2 mph (9
inches/second) is considered ``still air.'' While low  velocities
are desirable in winter months to prevent drafts, an air velocity
of at least 2 mph around large animals is necessary for  appreci-
able  hot  weather  cooling. To achieve this, the slot in an air-
intake ventilation system should be designed to impart a high air
entrance  velocity (about 1 sq in. of intake opening per 4 cfm of
fan capacity). If possible, deflect fresh air directly  onto  the

     Summer heat is removed by a ventilation system primarily  by
replacing hot air with cooler fresh air. Temperatures also can be
reduced by using heat from the air to evaporate moisture from the
floor, thus creating an evaporative cooling effect, and by taking
high-humidity respired air away from the  immediate  vicinity  of
the animals.

     Table 1 lists normally  recommended  ventilation  rates  for
pigs  housed  in enclosed buildings. Hot weather ventilation sys-
tems are typically designed to  maintain  an  inside  temperature
that  is  no more than 2o F to 5o F higher than outside conditions.
Required rates will depend on climate conditions as well  as  the
insulation  level  of the building. Hot weather rates recommended
for larger animals (sows in farrowing  and  gestation,  finishing
and  breeding  facilities) vary greatly around the United States.
In the northern areas, hot weather rates which are about one-half
those  in Table 1 may be sufficient while hot weather ventilation
rates in the Southeast may range to twice the values shown.

Table 1. Total per-head ventilation rates for enclosed swine
buildings during various times of the year.
                                  Cold      Mild       Hot
                                 weather   weather   weather
    Sow and litter                 20        80       500
    Pre-nursery pig (12-30 lb)      2        10        25
    Nursery pig (30-75 lb)          3        15        35
    Growing pig (75-150 lb)         7        24        75
    Finishing hog (150-220 lb)     10        35       120
    Gestation sow (325 lb)         12        40       150*
    Boar (400 lb)                  14        50       180*
*Use 300 per sow or boar in breeding facilities due to low animal
density   and   susceptability   to   poor  performance  at  high

     Air circulation systems, such as plastic air tubes and large
diameter  ceiling-hung  or  floor-mounted circulation fans, often
are used to increase air velocities around animals. These systems
are  especially  useful  in naturally ventilated buildings and in
wide (40 ft  or  more)  fan  ventilated  buildings.  See  PIH-41,
Maintenance  and Operation of Ventilation Fans for Hog Barns, and
PIH-60, Mechanical Ventilation  of  Swine  Buildings,for  further
information on the design of livestock ventilation systems.  Sum-
mer circulation fans should be sized at about  one-half  the  hot
weather  rate  given  in  Table  1. For example, a farrowing room
would be designed to exhaust 500 cfm per sow and provide circula-
tion fan capacity equal to 250 cfm (1/2 x 500) per sow. In natur-
ally ventilated buildings, locate the structure  on  high  ground
away  from  other structures and trees that might block air flow.
See PIH-60 and PIH-120 for information  on  sizing  openings  for
mechanical and non-mechanical ventilation systems.

Water Cooling Systems

Water Supply

     Animals must drink large quantities of water in hot  weather
if  their  evaporative heat loss system is to help them cool off.
Table 2 lists the summer water requirements  for  pigs.  Table  3
lists  the  nipple waterer flow rates recommended for pigs. Water
should be kept as cool as practical  in  order  to  achieve  best
weight  gains in summer. Cooled water can slightly increase daily
weight gain in very hot weather. Thus, water direct from  a  well
is  preferable  to  water  stored  in an above ground tank for an
extended period or from a shallow farm pond.

Table 2. Typical summertime water usage for pigs.*
                                                   Water per head
Type of animal                                      per day, gal

Sow + litter                                             8
Nursery pig                                              1
Growing pig                                              3
Finishing hog                                            5
Gestation sow                                            6
*Includes water use for  drinking  and  moderate  water  wastage.
Water cooling systems may increase usage.

Wet-Skin Cooling

     The pasture wallow has been used for many years for wet-skin
cooling.  In  addition,  the  mud pack acquired helps protect the
skin from the sun's rays.  Wallows located under shade  are  more
effective  in  improving  animal  comfort  than unshaded wallows,
because they are shielded from  the  sun's  rays  and  the  water
remains cooler.

     Substantial cooling is possible by wetting the animal's skin
and  allowing the moisture to evaporate. Research studies measur-
ing the performance of finishing hogs in hot weather reveal  that
animals  perform as well with sprinklers as they do with evapora-
tive cooling  of  inlet  air.  Air  movement  across  the  animal
increases the evaporation rate and improves cooling.

     In extremely hot weather, relief can be gained by hosing the
animals  down once every hour or so. This requires more water and
labor than a sprinkler system but can help during a crisis.

     Sprinkling is preferred to fogging, which uses smaller water
droplets.   Sprinkling cools the skin surface by wetting the skin
surface and allowing the  water  to  evaporate,  whereas  fogging
cools  the  air  and the air must then cool the animal. Also, the
smaller fog droplets drift with air movement.

     Animals cooled with sprinklers should be provided access  to
shade or shelter to avoid possible ``sunburn.''

     Most  sprinkler  systems  operate   by   using   thermostat-
controlled  timers  that wet the animal and then allow it to dry.
Sprinkler systems usually are designed to run for 1 to 2 min dur-
ing  each  30-min  period (a few operations use 1 to 2 min during
each 10-min period) when the temperature is above some set  value
(typically in the 80o F to 85o F range). Locate sprinklers over the
slots in a partially slotted floor or over the  dunging  area  in
solid floor systems.

Table 3. Nipple drinker recommendations for swine
                Pigs per       Nipple distance       MINIMUM flow
Stage           nipple         apart, inches         per minute

Nursery            10                12              1-1 1/2 cups
Grower           10-15               18                2-3 cups
Finisher           15               24-36              3-4 cups
Gestation          15                36                3-4 cups
Lactation          1                 NA                3-4 cups

     Tables 4 and 5 provide water line and nozzle  size  informa-
tion.  Provide  at least 0.02 gal of water per hour per finishing
hog (1 gal per 50 finishing hogs) for adequate sprinkler cooling.
If  the  available  nozzles  do  not provide the proper amount of
water at the available water pressure, either  adjust  the  water
pressure,  adjust the timer accordingly or use more than one noz-
zle per pen. While producers often construct sprinkler systems by
simply  punching  holes in polyethylene pipe with a 20 gauge nee-
dle, a specifically designed nozzle provides a better spray  pat-
tern and is less apt to become plugged.

Table 4. Nozzle sizes for sprinkler system (based on operation at
40 psi).
              Water                   Frequency of use
 Pigs      requirements      2 min/10 min         1 min/30 min
per pen      (gal/hr)      gal/min    gal/hr    gal/min    gal/hr

10             0.2          0.017       1        0.10         6
20             0.4          0.033       2        0.20        12
30             0.6          0.050       3        0.30        18

Table 5. Water line sizes for sprinkler systems.*
Pipe size     Class 160      Class 200     Schedule      Schedule
   ID            PVC            PVC           40            80

3/4 in.          7 gpm         6 gpm        4.5 gpm       3.5 gpm
1 in.           13 gpm        13 gpm        9 gpm         7 gpm
1 1/4 in.       25 gpm        23 gpm       18 gpm        15 gpm
1 1/2 in.       35 gpm        32 gpm       28 gpm        23 gpm
2 in.           55 gpm        55 gpm       50 gpm        45 gpm
2 1/2 in.       85 gpm        80 gpm       70 gpm        65 gpm
*Based on maximum pressure drop of 2 psi per 100 ft  or  velocity
less than 5 ft per second.

     Be sure to have an easily cleaned, in-line  sediment  filter
(100  mesh  strainer  or  cartridge  unit)  and  a timer-operated
solenoid valve in the line between the water source and the  noz-
zles (Figure 2). Nozzles are an especially important component of
any sprinkler system. Select  noncorrosive  nozzles  specifically
designed to furnish a solid cone of water droplets, not a mist or

     Drip cooling utilizing drip irrigation emitters  works  well
in  farrowing  houses.  These  systems  operate  at low pressure.
Obtain drippers rated at 0.5 to 1.0 gal/hr at the  manufacturer's
pressure  rating.  Control  the  drippers  with  a thermostat and
solenoid valve. Operate drippers  when  air  temperature  exceeds
85o F.

     Locate the water supply pipe (a  1/2  in.  polyethylene  can
deliver  150  gal/hr)  over the top bar of the stall about 20 in.
behind the front headgate. This location  reduces  feed  wetting,
keeps  young pigs dry, and provides effective sow cooling. Center
drippers over the sow's neck and shoulder area.  Do  not  install
drippers where water can flow into the creep area.

     Single nozzle drip systems can be used  in  individual  pens
such as boar pens.  Locate the nozzle in the dunging area.

Evaporative Cooling Systems

Operation Principles

     Evaporative coolers use the heat of  water  vaporization  to
cool  ventilation  air  in  the  same  way  that water sprayed on
animals evaporates and cools their skin.  The  incoming  ventila-
tion  air  is  passed  through a moist pad, where heat in the air
evaporates moisture into the air. This raises the relative  humi-
dity while lowering the temperature of the air.

     The lower the relative humidity of  the  incoming  air,  the
more  effective  the  evaporative cooling. This kind of cooler is
more effective in dry western states than in  the  midwestern  or
eastern  United  States. Even so, evaporative cooling can provide
some relief from heat stress  under  most  summer  conditions  in
these areas. Relative humidity drops as the air temperature rises
and is usually at its low point during the hottest  part  of  the
day.  Theoretically, a temperature drop of 18o F is possible under
typical midwestern summer conditions.  In  practice,  however,  a
temperature  drop  of  only  about  8o F  can be expected. The hot
weather ventilation rates shown in Table  1  should  be  used  to
design an evaporative cooler.

     Several types of evaporative coolers are available for  com-
mercial  use  in  livestock  buildings.  Most  were developed for
greenhouse or residential use.  Local  greenhouse  suppliers  are
excellent  sources  of information for this equipment. Most units
use a circulating pump to distribute water over  a  fibrous  pad.
Air  is  drawn through pads into the animal area. Routine mainte-
nance is essential to maintain the  system  in  proper  operating
condition (i.e., to control algae growth and dirt build-up).


     Figure 3 shows a  typical  evaporative  cooler  design.  The
water  distribution  system  usually  consists of a rigid plastic
pipe with spaced holes to allow the water to be distributed  uni-
formly  over  the  pads. A 2-in. pipe with 1/8-in. holes spaced 4
in. apart (4 ft water gauge pressure head) or  a  4-in.  x  4-in.
open  gutter  with  1/4-in. holes spaced 4 in. apart (2 in. water
gauge pressure head) will produce about the same flow  rate  over
100  linear ft of pad area, but a better practice is to size pipe
diameter, hole diameter and spacing for each system individually.

     The best procedure for sizing total pad area  is  to  follow
the manufacturer's specific recommendations for your location. In
the absence of specific  manufacturer  recommendations,  the  pad
area  needed (sq ft) can be approximated by dividing the ventila-
tion rate (in cfm) to be cooled by 150 for aspen pads, or by  250
for  cellulose honeycomb-style pads. The water sump should have a
capacity of at least 0.5 gal per sq ft of aspen pad, or  0.8  gal
per  sq  ft  of  4  in. thick cellulose pad. The flow rate to the
water distribution pipe over the pads should be at least 0.3  gal
per  min  (gpm)  per  ft of linear length of 2 in. to 4 in. thick
aspen pad (0.4 for aspen pad under desert conditions) or 0.5  for
4 in.  thick cellulose pad to ensure adequate wetting.

     A gutter sloped at 1 in. per 20 ft is  located  beneath  the
pads  to  collect  any water not evaporated and convey it back to
the sump to prevent water wastage.  Recycled  water  should  pass
through  an inclined 50 mesh screen before entering the sump. The
sump and open distribution gutter should be covered to  shut  out
sunlight  (to  control  algae growth) and to keep out insects and
other debris.  Make-up water to the sump is  normally  controlled
with  a  shutoff  valve.  Up to 1 gpm per 100 sq ft of pad can be
evaporated on hot, dry days.

     Set the thermostat so that the pump begins wetting pads when
the temperature reaches 80o F to 85o F. The pump should be wired so
that it shuts off before the fans. This allows the  pads  to  dry
out after use and minimize the buildup of algae growth.


     Pads made from woven aspen fibers must be replaced annually;
however,  cellulose and other types of pads with a useful life of
5 years or more are available now with some units.  Pads  usually
are  mounted either on the side or endwall, or on the roof. Wall-
mounted pads are easier to maintain and, therefore, are preferred
for  livestock  buildings.  Vertically  mounted  pads  should  be
checked periodically to eliminate  sagging,  resulting  in  voids
which  allow ventilation air to by-pass the wetted pads and enter
the building without being cooled.

     Pads should be hosed off at least once a month to wash  away
any trapped dust and sediment. Algae build-up in the recirculated
water system is sometimes a problem but can be controlled with  a
copper  sulfate  solution.  Some units use light-tight enclosures
around the pads to help control algae growth.

     Because water is  constantly  being  evaporated,  salts  and
other  impurities  build  up. Constantly bleeding off 1% to 2% of
the water (0.05 gpm per 1000 cfm of air cooled) will  help  flush
these  salts from the system as they are formed.  The entire sys-
tem also may be flushed  out  periodically,  with  the  frequency
depending  on  the  hardness of the water used. Install removable
caps or valves on the ends of the distribution lines  to  facili-
tate flushing.

Refrigerated Air Systems

     Refrigeration cooling systems are seldom used  in  livestock
buildings  because of their high installation and operating cost.
Unlike residential units, air conditioners in livestock buildings
usually  are  not installed to reuse room air because of the high
level of corrosive gases and dust in the air.  To  prevent  rapid
clogging and excessive maintenance, the air conditioner must con-
tinually cool incoming fresh air in a one-pass process. Some pro-
ducers use refrigerated air units for space cooling in their far-
rowing houses or in swine breeding units, and the systems do per-
form satisfactorily, except for the high operating cost.

Operation Principles

     Air conditioners both cool and  dehumidify  the  air  as  it
passes  over a cold, finned refrigeration evaporator coil. If the
air is cooled below the dew-point temperature,  moisture  in  the
air  condenses. The relative humidity of the air leaving the unit
is higher than the relative humidity of the incoming air  because
of  the  lower temperature, but it contains less moisture because
of the condensation. As this air is warmed  by  mixing  with  air
inside the building, its relative humidity decreases, enabling it
to pick up additional moisture.


     A ``ton of refrigeration'' is a term originating in the days
of  ice block cooling. It is defined as a cooling capacity of 200
Btu per min or 12,000 Btu per hr. For a well-insulated  building,
use 1 ton of refrigeration for each 275 cfm of conditioned venti-
lation air. To determine the  size  of  the  unit  needed  for  a
specific building, refer to the following example.
|Table 6. Air ventilation rates for swine in enclosed refrigerated |
|buildings.*                                                       |
|                                                                  |
|_________________________________________________________________ |
|Type of animal                          Ventilation rate per head |
|_________________________________________________________________ |
|                                                                  |
|Lactating sow                                    100 cfm          |
|Gestating sow (325 lb)                            40 cfm          |
|Boar (400 lb)                                     50 cfm          |
|Finishing hog (150 lb)                            30 cfm          |
|_________________________________________________________________ |
|                                                                  |

     Example: What size air conditioning unit is needed to cool a
20-sow  farrowing house? From Table 6, the total refrigerated air
ventilation rate is found to be 2000 cfm (100  cfm  x  20  sows).
Size  of  the cooling unit, therefore, should be about 7 1/4 tons
(2000 cfm : 275/ton).

     Earth-tempered air often is an  economical  form  of  refri-
gerated  air. See PIH-102, Earth Tempering of Ventilation Air, or
MWPS-34 Heating, Cooling, and Tempering Air for a  detailed  dis-
cussion of earth tempering and for specific design procedures.

Zone Cooling Systems

     Since, in hot weather, 50% to 60% of  animal  heat  loss  is
through  evaporation  from  the  respiratory tract and convection
from the skin surface, cooling the zone around the animal's  head
can be an effective cooling method. A supply of high-velocity air
around the head enables the animal to lose  more  heat  and  thus
remain  cooler.  Zone  cooling  does  not  satisfy all of the hot
weather ventilation needs. A conventional hot weather ventilation
system  sized  to remove air at the rate given in Table 1 also is

     Zone cooling is generally used only for crated  or  tethered
animals or a small number of animals in a small pen, such as in a
boar pen. In farrowing houses, zone cooling helps maintain a cool
environment for the sow while allowing higher temperatures in the
pig creep.

     Zone cooling systems can use either fresh  uncooled  air  or
refrigerated  air.  Evaporative cooled air is NOT recommended for
zone cooling systems because the high moisture content of the air
prevents  effective  dissipation  of respired moisture around the
animal's head.  Air  cooling  with  earth  tubes  or  other  non-
evaporative methods should be designed according to the amount of
temperature drop. If cooling is  as  efficient  as  refrigeration
(i.e.,  20o F or more drop in temperature), the same design can be


     A zone cooling system (Figure 4) has a main air supply  duct
open to the outside or to the cooling unit and downspouts or drop
ducts located as needed for the animals.

     The downspouts should be placed as close as possible to  the
animals'  heads.   They  should be constructed of nondestructible
material and well anchored if within the animal's reach.  If  the
duct  opening  is  too far above the animal, the cooled air mixes
with the surrounding air, both reducing its velocity and  raising
its  temperature.  Dampers  can be used on downspouts to shut off
the airflow when crates or pens are empty.

     Table 7 gives recommended air flow rates for  systems  using
uncooled  outside air or refrigerated air. Tables 8 and 9 present
supply duct and downspout sizes to  accommodate  various  airflow
rates.  These  suggested  minimum sizes permit an air velocity of
600 ft per min (fpm) through the supply duct and 800 fpm to  1000
fpm  through  the  downspouts.  The  trunk  ducts can be slightly
larger but should not be smaller if good air distribution  is  to
be  obtained.  Sizes  shown  for  downspouts are more critical in
maintaining the proper air exit velocity and should be adhered to

Table 7. Per-head air flow rates for zone cooling of swine.*
                                 Uncooled            Refrigerated
Type of animal                     air                   air

Farrowing sow                       70                    40
Gestating sow (325 lb)              35                    20
Boar (400 lb)                       55                    30
*Systems  using  zone  air  cooling  systems  should   still   be
ventilated at the hot weather rates shown in Table 1.

     If zone cooling ducts are used to supply refrigerated air in
summer  or fresh air in winter (as a part of a winter ventilation
system), they must be insulated (R = 6 minimum) to  prevent  con-
densation.  With  refrigerated air, insulation also will minimize
heat gain as the cooled  air  passes  through  the  duct  to  the

     The following example shows how to determine, from Tables 7,
8,  and 9, the airflow and duct size requirements of zone cooling
systems for a 20-sow farrowing house.

     Uncooled air. From Table 7, airflow in each downspout should
be  70  cfm,  and  in  the  supply duct it should be 1400 cfm (70
cfm/sow x 20 sows). From Tables 8 and 9, a proper downspout  size
for 70 cfm is 4 in. diameter, and the minimum trunk size for 1400
cfm is 18 in. x 20 in.

     Refrigerated air  cooling.  From  Table  7,  each  downspout
should  supply 40 cfm, while the supply duct supplies 800 cfm (40
cfm/sow x 20 sows). From  Tables  8  and  9,  this  airflow  rate
requires  a  downspout diameter of 3 in. and the trunk size of 12
in. x 20 in. Note that the size of the air  conditioner  required
for zone cooling is about 3 tons (800 cfm : 275 cfm/ton) compared
to 7 1/4 tons required to cool the entire building  (see  earlier

Table 8. Minimum supply duct sizes for zone cooling systems  (600
fpm air velocity).*
                     Inside duct dimensions if:

Air flow rate
within duct,                Rectangular,                 Round,
cu ft/min                    in. x in.                  diam, in.
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
*It is the minimum  cross  section  area,  not  the  actual  duct
dimensions  given inthe table, that is important. Almost any duct
shape of comparable size should deliver the same amount of air.

Table 9. Recommended downspout sizes  for  zone  cooling  systems
(800-1000 fpm air velocity).
                     Inside duct dimensions if:

Air flow rate
per sow,                    Rectangular,                 Round,
cfm                          in. x in.                  diam, in.
20                                2 x 2                   2 1/2
30                                2 x 3                   2 1/2
40                            2 1/2 x 3                       3
50                                3 x 3                   3 1/2
75                            3 x 4 1/2                       4
100                           4 x 4 1/2                       5
125                           4 x 5 1/2                       6
150                           4 x 6 1/2                       6
175                               4 x 8                       8
200                               6 x 6                       8
250                           6 x 7 1/2                       8


     The lack of a cooling system is a serious deficiency in many
buildings. Many pork producers experience enough loss due to poor
performance and animal deaths each summer to pay  for  a  cooling
system in a short time. Cooling systems need not be sophisticated
to be effective, but they must be selected and designed for  ease
of  maintenance. Reliability should be a primary consideration in
selecting a system.

     Suggested Reading: MWPS-34 Heating,  Cooling  and  Tempering
Air  for  Livestock Housing 1990 is available ($6.00 plus postage
and handling) from: Midwest Plan Service, 122 Davidson Hall, Iowa
State University, Ames, Iowa, 50011. Phone 515-294-4337.

      Abbreviations or Acronyms used in this publication

F                Fahrenheit
Btu              British thermal unit
ft or sq ft      feet or square foot
in or sq in      inches or square inches
lb               pounds
gal/hr           gallons per hour
gal/min or gpm   gallons per minute
psi              pounds per square inch
cfm              cubic feet per minute
fpm              feet per minute

List of Figures

Figure 1. Shades shield out the sun's rays and provide a cool ground
surface for the animals to lie on. Ideally, the high side of the shade
should be located on the north to maximize radiant heat loss from the
animals. See USDA Plan No. 5947 (12 ft x 16 ft shade) and No. 6257 (16
ft x 16 ft shade) available from the Agricultural Engineering Depar-
tment at your state Land Grant University.

Figure 2. Sprinkler cooling systems should be equipped with a timer-
operated solenoid valve, and an in-line sediment fitter (strainer).   

Figure 3. In a sidewall mounted evaporative cooling system, venti-
lation exhaust fans pull hot outside air through wet fiber pads.
Heat from the air is used to evaporate the water, thus lowering
temperatures but increasing the relative humidity. Consider modifying
the baffle for down-the-wall air flow for maximum benefit when the
cooling system is in operation.  

Figure 4. Zone cooling systems provide only a portion of total venti-
lation needs but are very effective, since high-velocity air is trans-
ported directly to the animals.   

REV 12/92 (7M)

Cooperative Extension Work in  Agriculture  and  Home  Economics,
State  of Indiana, Purdue University and U.S. Department of Agri-
culture Cooperating. H.A. Wadsworth,  Director,  West  Lafayette,
IN. Issued in furtherance of the Acts of May 8 and June 30, 1914.
It is the policy of the Cooperative Extension Service  of  Purdue
University  that  all  persons  shall  have equal opportunity and
             access to our programs and facilities.