Fans can also be placed in the outside wall to draw outside air into the barn through cooling panels. This method, the so-called tunnel ventilation system, can realize temperature reductions of as much as 8 to 12 C!

A good cooling system produces an air velocity at animal height of at least 2.5-3.0 m/sec throughout the barn. While the temperature of the air does not drop, the wind chill at this air velocity means the animals experience a temperature that is 2 to 4 C lower.