As the seasons transition and temperatures rise, is the building's ventilation system ready to do its job? Although automation and controllers are useful for managing a barn environment, ventilation equipment should get a check-up to ensure it can deliver the correct airflow and air speed throughout the barn.
Cleaning dust from fans and inlets and checking fan belts and motors is a start. Fans are rated to move a specified amount of air, measured in cubic feet per minute, when operating at a certain speed. If that speed is not met or the fan is dirty, air flow declines. Cooling systems such as sprinklers, drippers, and evaporative pads should also be inspected to make sure they are operating correctly.
The Iowa Pork Industry Center (IPIC) at Iowa State University has resources to help. Producers can use the summer ventilation checklist and the swine building ventilation system maintenance and troubleshooting guide to prepare for increased temperatures. IPIC also recently released “Heat Stress in Swine Production,” a publication that reviews research on the effects of heat stress in swine and includes common ventilation and heat stress mitigation strategies. Additional resources are also available on the Iowa Pork Industry Center website.
Keeping pigs cool
A properly designed and maintained ventilation system plays an important part in providing a good environment for pigs, but how does it keep them cool? Pigs can be cooled by both convection (air flowing around the pig) and evaporation (energy or heat used to change water to vapor).
As outside temperatures warm, cooling pigs by convection or air movement is the ventilation system’s main job. Pig size and temperature difference between the pig and the flowing air determine the amount of cooling for the pigs. During cold air temperatures, wind chill is considered negative, but the same principle can help cool pigs in warm conditions. The greater the temperature difference between the air and the pig’s skin, the greater the cooling effect. In addition, air flow of approximately 3.5 miles per hour, or 350 to 400 feet per minute at the pig level, maximizes the cooling effect of convection. As air temperatures rise and get closer to the pig’s skin temperature, air flow and convection are less effective at cooling the pig.
When temperatures get too warm and convection is not as effective, evaporation is needed. Sprinklers, drippers, evaporative pads, or cool cells all use evaporative cooling to reduce heat stress. Using evaporative cooling at air temperatures of 80ºF or more for grow-finish and breeding swine is a common guideline. Sprinklers and drippers should be set to wet the pig or other surfaces for a short period of time. After the pig or surfaces are wet, time is needed for the evaporation of that moisture to cool the pig and surrounding air. A common setting is two minutes of sprinkling followed by 15 minutes off to allow for evaporation.
Evaporative pads or cool cells use evaporation to cool the air coming into the building. The main limitation of evaporative cooling is high humidity, which limits how much moisture can be changed to vapor. If too much moisture is added by leaving sprinklers on for too long, the cooling effect is minimized. Moving air to maximize convection and then adding evaporation are the main ways to keep pigs cool in warm temperatures.
Summary
Ventilation systems should be inspected seasonally to ensure everything is working correctly. Use the summer ventilation checklist to facilitate maintenance and prepare the barn for higher temperatures.
Air speed utilizes convection to cool the pig to some extent, but higher temperatures require evaporation to minimize heat stress.
For more information, contact an Iowa State University Extension and Outreach swine field specialist or email ipic@iastate.edu.
