HOUSING                                           PIH-92


   Energy Conservation in Ventilating and Heating Swine Buildings

Robert L. Fehr, University of Kentucky
Raymond L. Huhnke, Oklahoma State University

Maynard Hogberg, Michigan State University
Larry Jacobson, University of Minnesota
Duane Miksch, University of Kentucky
David Shelton, University of Nebraska

Energy Inputs

     Energy is used in swine  facilities  for  the  operation  of
fans,  lighting, feed handling, creep heaters, water heaters, and
supplemental space heaters. This fact sheet will discuss ways  to
save  energy  used  for  operating a ventilation system including
supplemental heating. Most  mechanical  ventilation  systems  use
energy to reduce the management required to maintain a productive
environment.  Usually, reducing energy use increases the level of
management  required.  Some methods of saving energy may increase
other production costs, such as feed, enough to offset the  value
of  any  monetary  savings  for  energy. There are ways to reduce
energy use without adversely affecting feed utilization or animal

Environmental Control

     Ventilation Principles. The primary goal  of  a  ventilation
system  is  to modify the environment to improve production while
maintaining acceptable air quality levels for  workers.  The  way
ventilation  systems  operate  has  a major impact on energy use,
especially supplemental heating. Ventilation systems are designed
to vary air flows from minimum ventilation rates in the winter to
maximum ventilation rates in the summer (Table 1).

     Ventilation rates  vary  because  there  are  different  air
exchange needs at different outside temperatures. The ventilation
system must limit temperature rise during  hot  weather,  control
temperature  during  mild  weather,  control humidity during cold
weather, and control odors and gases.

     When the outside air temperature is greater than the desired
inside air temperature, the ventilation system can only limit the
temperature rise of the air as  it  passes  through  a  building,
unless  a  cooling device is used.  The air temperature increases
as it moves through the building because of the heat added by the
animals,  lights,  creep heaters, motors, etc. As the outside air
temperature falls below the inside air  temperature,  temperature
control  is  achieved  by altering the ventilation rate until the
heat losses from the ventilation air and building shell equal the
heat added. As the ventilation rate decreases, the relative humi-
dity in the building increases. The ventilation rate must then be
adjusted  to  balance the moisture removed by the ventilation air
with the moisture produced in the building.  During  low  outside
temperatures,  when  the ventilation rate needed to control humi-
dity is greater than the rate to control temperature,  a  supple-
mental  heat  source  must  be added to maintain the building air

Table 1. Total Per-head Ventilation Rates for Swine Buildings
During Various Times of the Year.
                         Cold             Mild              Hot
                        Weather          Weather          Weather
Sow & litter              20               80               500
Pre-nursery                2               10               25
pig (12-30 lb)
Nursery pig                3               15               35
(30-75 lb)
Growing pig                7               24               75
(75-150 lb)
Finishing hog             10               35               120
(150-220 lb)
Gestation sow             12               40               300
(325 lb)
Boar (400 lb)             14               50               300

     The level of odors in a swine  facility  is  another  factor
affecting  the  minimum  ventilation rate. Odors will increase in
any facility as the ventilation rate decreases. The  most  impor-
tant  energy  conservation  techniques  are those that reduce the
ventilation rate  as  much  as  possible  while  maintaining  the
minimum  allowable  room temperature as well as good moisture and
odor control.

     Effective  Temperature.  The  ventilation  rate  should   be
managed  to provide an environmental temperature that will maxim-
ize animal performance. The environmental temperature required is
determined  by  several  factors  including  air temperature, air
speed, humidity, floor type, radiation levels,  animal  size  and
group  size.  Together  these factors determine an effective tem-
perature.  The effective temperature for an animal is similar  to
the  wind chill index for humans. Comfort levels must be based on
the effective temperature rather than on the actual air  tempera-
ture  alone.  For  example,  a  nursery  that has no drafts, warm
walls, dry straw on the floor, and an air temperature  of  70o   F
could  have a similar effective temperature as a nursery that has
drafts, cold walls, a wet concrete floor, and an air  temperature
of  95o  F. The use of hovers in farrowing rooms is a good example
of providing an area for the small pigs with a  different  effec-
tive  temperature  than the entire room. Effective temperature is
more important to animals than air temperature  5  ft  above  the
floor.  Locate  ventilation  controls  as close to the animals as
practical to provide  better  control  of  the  air  temperature.
Desirable  Humidity  Levels.  A relative humidity between 50% and
70% is desirable in most swine buildings. Higher humidities  con-
tribute to rapid equipment and  building deterioration. Waterers,
manure, wet floors, gutters and  water  vapor  from  an  animal's
lungs  and  skin  all  contribute  to  the  moisture that must be
removed. At present, there is no reliable, inexpensive device  to
sense  and control relative humidity in the corrosive environment
of swine buildings.  Therefore, ventilation  rates  for  humidity
control  are  based  on  room  moisture  production  estimates or
experience. The humidity level in the building can be altered  by
proper  adjustment of the ventilation rate. To raise the humidity
level, the ventilation rate is decreased. To reduce the  humidity
level, the ventilation rate is increased.

     Measuring Humidity Levels.   The  most  reliable  and  least
expensive  method  of  measuring the relative humidity level in a
swine building is with a sling psychrometer. The sling psychrome-
ter  consists of two matched thermometers mounted side-by-side in
a holder, with some provision for whirling the device through the
air  (Figure  1).  The measuring bulb of one thermometer is bare,
while the other is covered with a wetted  cloth  or  wick.  After
being  whirled  for  several minutes, both thermometers are read.
Using these two temperatures, the relative humidity is then  read
from a chart or sliding scale.

     Odor Levels. The level of odor in a swine facility is  often
the  limiting factor in determining the minimum ventilation rate.
Odor production varies with  the  type  of  manure  handling  and
storage  system. If odors in a facility become too great when the
ventilation rate is decreased, a producer  has  two  choices:  1)
alter  the  manure management system to decrease the odor produc-
tion rate, or 2) increase the  ventilation  rate  to  dilute  the
odor.  For  many  swine  buildings,  the  odor level will require
higher ventilation rates than the  minimum  level  allowable  for
humidity  control.  For  this  reason  the  trend is to store the
manure outside the building. Under-slat, exhaust ventilation sys-
tems  can  aid  in  removing  odors in some buildings with partly
slotted floors.

     The effect of swine building odors and gases on  both  swine
and  humans is being researched at several universities. Although
limited data are available, high levels of dust and  some  manure
gases  have  been  shown to contribute to respiratory problems in
both humans and swine.

Table 2. Effect of Ventilation Rate and  Insulation  Level  on  a
Farrowing Building's Energy Use.
                                          Building Insulation Level
                             R-10                   R-20   
            Average   Minimum                    Minimum                
            winter    outside      Supplemental  outside     Supplemental
            building  temperature  heat          temperature heat         
Ventilation relative  requiring    requirement   requiring   requirement  
  rate      humidity  no heat      at 0o F 2     no heat     at 0o F 2   
cfm/sow 1   %         o F          Btuh/sow 3    o F         Btuh/sow 3
20 (heat    67      22         520         4          60           
20          67      38         1300        28         810          
30          50      46         2020        42         1560         
40          40      50         2770        48         2320         

Contd .. Table 2.  
                                          Building Insulation Level
              Average          Minimum
              winter           outside      Supplemental
              building         temperature  heat
Ventilation   relative         requiring    requirement
  rate        humidity         no heat      at 0o F 2     
cfm/sow 1     %                o F          Btuh/sow 3
20 (heat       67               -6             0
20             67               26           650
30             50               40          1400
40             40               46          2160
1cfm/sow = cubic feet per minute per sow.
2Outside air temperature.
3Btuh/sow = Btu per hour per sow.
4All ventilation air provided by a 50% efficient heat  exchanger.
Assumptions:  Twenty-crate  farrowing building, animal heat only,
70o F building temperature, partly slotted floor.

Minimum Ventilation Rate

     The minimum ventilation rate  provided  by  the  ventilation
system in a swine building will have a major impact on the energy
required for supplemental heat.  Increasing the minimum  ventila-
tion  rate  in  a  typical farrowing building from 20 to 30 cubic
feet per minute (cfm) per sow and litter would increase the  sup-
plemental heat requirement at an outside temperature of 0o  F from
1300 to 2020 Btu per hour per sow (Table 2) and increase the out-
side  temperature  below which supplemental heat is required from
38o  to 46o  F. The minimum ventilation rate can  be  reduced  pro-
vided humidity levels are maintained at desirable levels and odor
levels do not become unacceptable.

     Altering Minimum Ventilation Rate. The preferred  method  of
providing  a minimum ventilation rate is to use a small, continu-
ously running fan. The ventilation rate provided by this  fan  is
calculated from the number and size of pigs in the building. How-
ever, the ventilation rate calculated  may  need  to  be  altered
because  the  ventilation  rate  calculation  is based on average
moisture production estimates, the  calculated  ventilation  rate
may  not  match airflow rates provided by available fans, and the
number of animals and their weight  varies.  Approaches  used  to
alter  the  minimum ventilation rate include multiple small fans,
timer-controlled fans, variable-speed fans and a damper or  slid-
ing throttle controlled ducted fan. See PIH-60, Mechanical Venti-
lation of Swine Buildings and PIH-41, Maintenance  and  Operation
of Ventilation Fans for Hog Barns for more detailed information.

     Air Distribution Problems.  It  becomes  more  difficult  to
maintain   proper  air  distribution  as  ventilation  rates  are
lowered. Ventilation systems with adjustable  air  inlet  baffles
running  the length of one or both sidewalls have difficulty pro-
viding small enough openings to allow even  air  distribution  in
the  room  when ventilating at minimum rates. Unplanned openings,
such as poorly fitting  doors,  fan  shutters  and  cracks,  also
hinder  proper  air distribution.  A static pressure gauge can be
used to check if the incoming air is moving fast enough  to  pro-
vide  adequate mixing and to prevent it from settling too rapidly
and thus chilling the pigs. When the baffle is properly adjusted,
the  static  pressure gauge should read at least 0.05 inches. The
surface near the inlet (within 8 ft) should be free  of  obstruc-
tions that could deflect the cold air onto the animals.

     Some ventilation systems use a pressurized tube or  duct  to
distribute  the incoming air. These systems mix incoming air with
room air to help prevent cold  drafts.  Since  tube  distribution
systems  use  only  one  air  inlet for the winter, they are well
adapted to distributing air from some air tempering systems, such
as heat exchangers, earth-tube systems, and pre-heat rooms.

     Small facilities with low minimum winter  ventilation  rates
may  require  small circulation fans in the animal space. The air
should move in a circular pattern around the room without  creat-
ing drafts on the animals.

Building Layout

     Energy conservation is important during the planning of  new
swine  production  facilities.  Beyond  the  obvious technique of
additional insulation, there is often a benefit  from  minimizing
exterior  walls.  The  move  toward smaller farrowing and nursery
rooms that allow all-in, all-out operation has resulted in  these
smaller  rooms  being  grouped in one larger building (Figure 2).
This grouping of smaller rooms results in a reduced area for heat
loss  through the walls and foundation. For example, a 24 ft x 36
ft farrowing room constructed with normal insulation levels, hav-
ing  two  rooms side-by-side reduces the wall and foundation loss
area by 30%. Placing 4 rooms side-by-side reduces this heat  loss
area by 45%.


     Temperature control is partially achieved by balancing  heat
losses to the ventilation air and through the building shell with
heat gains. Reducing the heat loss  through  the  building  shell
extends the temperature range over which the ventilation rate can
maintain temperature control. Swine buildings should be insulated
to  the  minimum  levels  given  in  Figure  3,  using techniques
described in PIH-65, Insulation for Swine Housing.

     A farrowing building can be used to  illustrate  the  impor-
tance of adequate insulation to save energy. The higher the level
of insulation, the lower the outside temperature must  be  before
supplemental  heat is required. For example, supplemental heat is
required in a farrowing building with an average  R-value  of  10
when  the  outside  temperature  is below 38o  F (Table 2). If the
average R-value is increased  to  20,  no  supplemental  heat  is
needed until the outside temperature drops below 28o  F. Note that
the outside temperature below which supplemental heat is required
is  reduced  only  2o   to 26o  F by increasing the average R-value
from 20 to 30. Therefore, massive quantities  of  insulation  are
not  economically  justifiable. The majority of heat loss from an
adequately insulated swine building is via the ventilation system
not through the building shell.

Thermostat Setting

     Lowering the thermostat setting on the  supplemental  heater
saves  energy two ways. First, it allows ventilation rate to con-
trol inside temperature at lower outside temperatures and second,
it  reduces  the  amount  of supplemental heat energy required to
maintain the inside air temperature. For  example,  reducing  the
temperature  in  a farrowing building from 70o  F to 60o  F reduces
the supplemental heat requirement at  0o   F  outside  temperature
from 1300 to 710 Btu per hour per sow (Table 3). In addition, the
outside temperature below which supplemental heat is required  is
reduced from 38o  F to 22o  F. Cooler air can hold less moisture so
as the inside temperature is reduced the relative humidity  level
may rise. When reducing the thermostat setting, caution should be
used to insure that animal performance and health do not suffer.

Table 3. Effect of Building Temperature and Insulation Level on a
Farrowing Building's Energy Use.
                                          Building Insulation Level
                             R-10                   R-20   
            Average   Minimum                    Minimum                
            winter    outside      Supplemental  outside     Supplemental
            building  temperature  heat          temperature heat         
Building    relative  requiring    requirement   requiring   requirement  
temperature humidity  no heat      at 0o F 2     no heat     at 0o F 2   
cfm/sow 1   %         o F          Btuh/sow 3    o F         Btuh/sow 3

60            72       22           710          12           320
70            67       38           1300         28           810
80            60       54           1830         48           1300

Contd .. Table 3.  
                                          Building Insulation Level
              Average          Minimum
              winter           outside      Supplemental
              building         temperature  heat
Building      relative         requiring    requirement
temperature   humidity         no heat      at 0o F 2     
cfm/sow 1     %                o F          Btuh/sow 3

60              72               8            200
70              67              26            650
80              60              46            1300


1Outside air temperature.
2Btuh/sow = Btu per hour per sow.  Assumptions: 20 cfm  per  sow,
20-sow  farrowing  building,  animal  heat  only,  partly slotted

     Thermostats that control fans (except the minimum rate  fan)
should  be set a minimum of 4o  F above the heater thermostat set-
ting or the preferred method is to have the heater and  fan  con-
trols interlocked or operated by the same controller. If thermos-
tats are not set properly, ventilation fans that control tempera-
ture may run when the heater is operating. This wastes energy.

Ventilation Air Tempering Methods

     The range over which the ventilation rate can  maintain  the
temperature  of  a swine building also can be extended by warming
the intake air. Several methods, such as heat  exchangers,  solar
walls,  and  earth  tubes  are used as air tempering systems. For
example, if a 50% efficient heat exchanger is  used  in  a  well-
insulated  farrowing  room  (R-20),  it  would decrease the lower
limit of the outside temperature from 38o  F to 22o   F,  Table  2,
above  which  the  ventilation rate can maintain the desired room
temperature. The design and economic feasibility of air tempering
methods  are  beyond  the scope of this fact sheet.  However, use
the energy conservation measures described  in  this  fact  sheet
before  considering  air tempering methods. Care must be taken to
insure that air tempering systems do not increase energy  use  or
adversely affect the air quality.

     Heat Exchangers. Heat exchangers are  designed  to  transfer
heat  from  the  exhaust  air to the intake air. A parallel-plate
heat exchanger separates exhaust and intake air by  thin  plates.
These  units  of  the heat normally lost in the exhaust air. How-
ever, they have problems with dirt, moisture and  freezing.  Heat
exchangers  should include methods for easy cleaning and defrost-
ing. Heat exchangers are  most  effective  in  saving  energy  at
warmer room temperatures and when the outside temperature is low.
For more detailed information see  PIH-124,  Heat  Exchangers  in
Swine Facilities.

     Solar Energy. Because the sun is free and provides a readily
available  and  endless  source of energy, it would seem to be an
attractive energy source for swine  facilities.  Some  facilities
make  use  of solar collection by allowing ventilation air in the
winter to enter through the attic of the building.

     Solar systems for swine facilities can be either  a  passive
or  active  type.   Passive  systems  are a combination of south-
facing windows and a proper roof overhang which allows the build-
ing to collect the solar energy. Passive systems in farrowing and
nursery units where heating is required  may  need  extra  energy
because of their large window surfaces.

     Active systems require methods for collecting,  transferring
and  storing  solar  energy.  Active systems allow for heat to be
stored in one location and used elsewhere. Without  a  method  of
storage,  an  active  system  may  provide more solar energy than
necessary during clear days and not enough heat energy at  night.
Solar  systems  must be properly designed as described in PIH-90,
Solar Heating for Swine Buildings.

     Earth-Tube Systems. Earth-tube heat exchangers use soil as a
heat  sink or source for tempering the ventilating air. Depending
on the season, air is heated or cooled as it is drawn  through  a
buried  tube.  The temperature 7 to 10 feet underground is nearly
constant throughout the year.

     Both soil characteristics and air-tube parameters affect the
performance  of  the  system.  Soil  characteristics include soil
type, moisture  content,  and  water  table  elevation.  Air-tube
parameters include diameter, length, depth of placement, spacing,
flow rate, and the shape of the  tube.  Typically,  nonperforated
corrugated  plastic  drainage  tile is used because it is readily
available and inexpensive. The corrugations increase the  surface
area  of  the  pipe and amount of air turbulence, which increases
the heat-transfer rate. For more detailed  information  see  PIH-
102, Earth Tempering of Ventilation Air.

     Animal Density. Keeping a building as  full  of  animals  as
practical  will  keep  the animal heat input as high as possible.
This can generally be achieved by proper sizing of  buildings  or
rooms  during initial design to insure that the buildings fit the
production schedule. Some designs have  been  proposed  to  group
larger numbers of animals together to increase the heat input. An
example would be a nursery in combination  with  a  farrowing  or
gestation  room.   These designs are not recommended because they
prevent the use of all-in, all-out production, may compromise the
managers'  ability to maintain proper sanitation, or fail to pro-
vide proper temperatures for animals of different ages.

Fan Selection

     A rating system for fan efficiency is now being used by most
fan  manufacturers to help select energy efficient fans. Fans are
rated for the amount of air moved per watt  of  electricity  con-
sumed  (cfm/watt).  The higher the number, the more efficient the
fan is at moving air, which results in lower operating costs. Fan
ratings  typically  vary  from 5 to 25 cfm/watt, with larger fans
generally being more efficient.  Studies  on  36-inch  fans  have
shown  ratings  from  10  to 23 cfm/watt. Selecting fans based on
their ratings reduces operating costs. During a typical summer in
the  Midwest,  fans  operate at their maximum rates approximately
2,000 hours per year. In this case, a 10,000 cfm fan  with  a  10
cfm/watt  rating  would result in 2,000 kwh's of electricity used
while a 10,000 cfm fan with a 23 cfm/watt rating would  use  only
870  kwh's  of electricity. At 9 cents per kwh, the difference in
operating cost between the two  fans  would  be  $102  per  year.
Energy savings are possible when trying to limit temperature rise
in the summer by using more efficient fans. However, when select-
ing  fans  for use in controlling humidity levels in winter, more
consideration should be given to their  ability  to  provide  the
proper ventilation rate rather than their efficiency ratings.


     Energy use in swine buildings can be reduced if  a  producer
is willing to increase the level of management of the heating and
ventilation system.  Ventilation systems are designed on the best
information  available;  however,  the information is for average
conditions, not necessarily those in your buildings  or  climate.
Proper management of a ventilation system to save energy includes
periodic measurement of temperatures and relative humidity levels
in  the  buildings.  However,  an  animal  zone  environment that
achieves the maximum production efficiency  and  health  is  more
important than sacrificing the environment for energy savings.

List of Figures

Figure 1. Sling psychrometer used to measure relative humidity.

Figure 2. Typical layout of rooms grouped for energy conservation.

Figure 3. Recommended minimum insulation levels for controlled
enviroment swine buildings.

REV 6/91 (7M)

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