Defrost is a mandatory process for any industrial air cooler operating at temperatures below freezing. At freezing temperatures frost builds up on the evaporator fins, causing units to lose cooling capacity and efficiency. Frost is normally removed by heating the evaporator to the point that the frost is melted and then drained away. The heating process uses energy which comes at a cost, however. Depending on frost load, temperature, fin spacing, etc., a typical defrost will cost somewhere around $0.15 to $0.20 per cycle per TR (Cole 1989).