The horizontal air flow, or HAF, concept utilizes the principle that air moving in a coherent horizontal pattern in a building, like a greenhouse, needs only enough energy to overcome turbulence and friction loss to keep it moving. In other words, you just have to “kick it along.” Small, 1/10- to 1/15-horsepower circulating fans work well in providing the air movement needed. These are made to move air with little resistance as compared to exhaust fans that have blades designed to overcome the resistance of air moving through louvers or vents, thus requiring more energy to operate.
For more information: Horizontal Air Flow Is Best for Greenhouse Air Circulation.
Contributor: Vern Grubinger, University of Vermont