Pork production facilities built and operated in the 21st century need to provide optimum environmental conditions to maximize production efficiency and provide a safe and healthy environment for pigs and workers while conserving energy. To accomplish these goals requires a fully integrated ventilation system that is specifically designed and installed for the specific barn and animals housed.
High-quality management and operation of the ventilation system is as important as selecting the proper ventilation components, such as fans, air inlets and heaters. Control of the air exchange or ventilation rates, adjustment of air inlets and operation of heating and cooling systems need to be regulated with an electronic controller. But it is very important that the person(s) managing the pig barn understand how the ventilation system works and how it can be adjusted to maximize the system’s effectiveness.
The main goal of a ventilation system in a swine barn is to provide an optimum environment for the pigs. The barn’s environmental parameters include room temperature and humidity, air speed across the animals, indoor air quality (primarily gas and dust concentrations), plus other features, such as light and noise levels, and other building conditions conducive to the animals’ comfort and well-being.
The primary parameter for measuring and controlling the quality of the environment and, thus, the ventilation system, is room air temperature. The ventilation system is regulated by a temperature sensor(s) connected to an electronic controller, which determines the air flow rate (by turning exhaust fans on and off), adjusts air inlets or curtains, and turns heaters on and off.
There are a number of different types of ventilation systems that can be used in hog buildings, but by far the most common is a negative-pressure (vacuum) mechanical system (Figure 1). For this type of system, exhaust fans create a slight negative air pressure inside the building, and this “static” pressure difference is why air enters the barn through ceiling or wall inlets. The air exchange or ventilation rate for the barn is determined by the number and size of the exhaust fans in this type of ventilation system.
Some barns have sidewall curtains (vs. solid walls) that are closed tightly during cold weather and operate under a negative pressure during that period of time. However, during warm weather, sidewall curtains are opened, voiding the negative pressure so the system reverts to a natural ventilation system that is driven by the wind.
The amount of air exchange or the ventilation rates for different sizes of pigs can be found in Midwest Plan Service (MWPS) shown in Table 1 or from similar publications, which have been calculated from heat and moisture balances of pigs in an insulated building.
The minimum ventilation rate, such as the 20 cu. ft./min. (cfm) for sows and litters in a farrowing facility, is designed to control the moisture produced by the sows, pigs and other sources. The other two ventilation rates for mild and hot weather are based on controlling the heat produced and, thus, the barn’s air temperatures.
Supplemental heat may be necessary in farrowing or nursery barns during cool or cold conditions, as well as in finishing barns during extreme cold weather. The goals are to maintain an acceptable room temperature and to make up for the heat lost from the minimum ventilation rate. Heaters must be properly sized and controlled so they work with the other components (fans, inlets) of the ventilation system. Otherwise, they can cause large room temperature fluctuations and high energy bills.
Much of the time, up to 95% in finishing barns, the ventilation system is trying to remove the heat produced by the pigs and regulate the barn’s temperature by limiting the rise in barn temperature during warm or hot days.
Figure 2 shows the different ways heat is transferred from the pig to the air in the building. Most of the heat is removed from the pigs by forced convection (air flowing over the pig) until air temperatures in the barn get too warm — between 70 and 85°F, depending on the size of the pig — and then evaporation (periodic wetting and drying of the pig’s skin by water sprinkling) must be used to keep pigs in a thermoneutral state.
Finishing pigs, especially, produce a tremendous amount of heat. Recent simulated studies at the University of Illinois measured the impact of losing electrical power and ventilation in a finishing barn with pigs averaging over 200 lb. Their results showed air temperatures will rise about 1° F/min., so in less than 30 minutes, barn temperatures can exceed 100°F and pigs may be lost due to heat exhaustion.
To demonstrate the effect of temperatures on pig performance, Figure 3 shows the relative impact (percent of maximum) that room temperature can have on feed intake, feed efficiency and growth rate. This study, conducted at the University of Kentucky using 1990 genetics and pigs weighing more than 150 lb., shows that growth rate peaks at about 60°F, while optimum feed efficiency occurs at about 68°F.
An estimate of the thermoneutral range is shown by the red bars in Figure 3, which should be the target or set-point temperature range for the barn’s ventilation system. In the summer, when outside temperatures are above 70°F, room temperatures will rise above the thermoneutral range and pigs will become heat stressed.
Evaporative cooling systems such as misters and sprinklers can reduce heat stress and the obvious production losses until outside temperatures reach 85-90°F and/or humidity levels or dew point temperatures are high. Evaporative cooling systems become ineffective at these high temperatures and humidity levels and pigs stop eating and growing. Thus, producers need to run barns cooler during normal summer conditions and possibly explore non-evaporative cooling techniques to avoid slow- or no-growth periods.
The challenge to keep pigs cool is further complicated by modern genetics. Today’s fast-growing, leaner pigs produce 20% more body heat than pigs from the 1990s, when Midwest Plan Service (MWPS) and other designers determined the ventilation rate recommendations for most hog buildings. Therefore, the thermoneutral zone of the present-day pig response shown in Figure 3 would shift to the left, lowering barn set-point temperatures another 2-3°F.
Four common ventilation system problems seen in pig barns today and their potential solutions include:
1. Inadequate insulation of the building shell. Pig buildings need to be well insulated, typically with a minimum R-value of 15 in the walls, R-25 in the ceiling, and at least R-5 on a perimeter concrete foundation or “knee” wall. These levels of insulation will provide a sufficiently warm surface temperature to prevent condensation during cold weather and prevent radiate heat loss for pigs to cold surfaces (i.e., non-insulated knee wall). Proper insulation will also help prevent the surfaces of walls, ceilings and roofs from getting too hot and transmitting heat by radiation to the pigs during hot conditions.
2. Inability to maintain static pressure in the building, which is needed to make the ventilation system functional. A fundamental criterion of a mechanical ventilation system is a slight negative pressure (i.e., 0.05 to 0.1 in. of water gauge) in the barn so the ventilation system can function properly. The building shell must be reasonably tight so the exhaust fans will create the static pressure.
If there are too many leaks in the barn or only variable-speed exhaust fans running slowly, not enough static pressure is created and inadequate air exchange and air distribution will result. Often, insulating the building will help tighten up the barn and solve this and these problems.
3. Controller set-point or barn target temperatures set too high and with differentials that are too small. Modern controllers regulate the major components of ventilation systems — fans, air inlets and heaters. All controllers allow for the selection of the barn’s target or set-point temperature, as well as the room temperature steps or differentials at which additional fans are activated. Often, this target temperature is set higher than what the pigs are comfortable with, based on the earlier discussion of thermoneutral zones for growing pigs.
Also, there is a tendency to set the temperature steps in too-small increments (0.5 to 1°F), which can result in fans turning on and off (cycling) in short periods of time and creating wide temperature variations in the barn. It is best to have larger differential settings (1.5 to 2°F) to allow the controller’s sensors time to respond to changes in the building’s environment, which will result in more uniform room temperatures.
4. Oversized heaters. Most U.S. pig buildings require heaters to provide supplemental heat during extreme cold conditions or when young pigs are placed in nurseries and wean-to-finish barns. Generally, these heaters are non-vented, gas-fired units. Many are much larger than they need to be, which can cause large temperature swings and high energy bills.
When the controller activates these large heaters (up to 250,000 Btu./hr), they generate large bursts of hot air and, typically, before the response is detected by the controller temperature sensor, cause the barn’s temperature to increase so much that additional exhaust fans are activated to cool the barn. As the additional fans are running, room temperature drops and the heater is again activated and the cycle continues.
This overshooting of room temperatures by oversized heaters can be easily solved by replacing them with smaller heaters or by adjusting the heater to reduce the output to about 60% of its maximum output. These so-called “green value” buttons on heaters can greatly reduce or eliminate this overshooting problem and save a tremendous amount of energy (LP gas) and money.
With today’s higher production costs, it is essential that producers provide an environment in which pigs can maximize their genetic performance potential and minimize energy and feed use.