HOUSING PIH-92
PURDUE UNIVERSITY. COOPERATIVE EXTENSION SERVICE.
WEST LAFAYETTE, INDIANA
Energy Conservation in Ventilating and Heating Swine Buildings
Authors
Robert L. Fehr, University of Kentucky
Raymond L. Huhnke, Oklahoma State University
Reviewers
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
performance.
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
temperature.
Table 1. Total Per-head Ventilation Rates for Swine Buildings
During Various Times of the Year.
_________________________________________________________________
Cold Mild Hot
Weather Weather Weather
_________________________________________________________________
-cfm-
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
exchanger)4
20 67 38 1300 28 810
30 50 46 2020 42 1560
40 40 50 2770 48 2320
______________________________________________________________________
Contd .. Table 2.
______________________________________________________________________
Building Insulation Level
__________________________________________________
R-30
__________________________________________________
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
exchanger)4
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%.
Insulation
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
__________________________________________________
R-30
__________________________________________________
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
floor.
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.
Summary
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)
______________________________________________
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.
.