Assistant Professor of Agricultural and Biosystems Engineering
Iowa State University
The environment inside our livestock and poultry houses is important for maintaining a productive and healthy herd or flock. Ventilation or fresh air exchange is important to remove undesirable moisture and noxious gases during winter months and in summer, make sure the indoor temperature is not too much warmer than outdoors. Ventilation can be achieved using mechanical equipment, such as fans and inlets, or using thermal buoyancy and wind. Mechanical systems are more technology advanced, fairly well automated, and more expensive. In comparison, natural ventilation is relatively simple and inexpensive, but may require more management.
The climate in Iowa lends itself well to producers utilizing natural ventilation because the winters are cold and nighttime lows often go below desired room temperature. Because of this, there is a temperature difference (gradient) between inside and outside coupled with the fact that warmer air rises, we can create natural air exchange. Alternatively, in the summer, during the hottest parts of the day, wind can blow past the animals inside creating a cooling effect. This same wind is also often experienced in winter, which sometimes makes management of naturally ventilated barns a challenge. This is where mechanical systems are advantageous and can help provide a more consistent environment.
The best way to utilize natural airflow is management of openings and facility layout. Small openings have to be well controlled to promote good air distribution and exchange. During cold weather or minimal ventilation, this will typically require small openings around the house and a chimney exhaust. Cold air enters the house, is distributed, accumulates heat and moisture from the animals, then rises and is exhausted out through the chimney. The best approach for capturing summertime wind is to have the long axis of the building running east-west, this allows for an opening to face south. Local terrain, proximately to other buildings or trees can have a substantial impact on summertime wind entering the house.
Ventilation equipment and management can be as complicated as the user desires. That said, the systems can be relatively inexpensive and only consists of a few fans, switches, thermostat, and curtains/louvers/inlets/etc. Alternatively, modern technology has promoted internet-enabled, “smart” controllers that can be operated from one’s smartphone. The principles of indoor environment and ventilation have remained unchanged since animals were first moved inside; however, the approach, technology, and producer goals have fundamentally changed over time impact how we create and manage ventilation today.