A ton of refrigeration (commonly abbreviated as TR) is a unit of power used in some countries (especially in North America) to describe the heat-extraction capacity of refrigeration and air conditioning equipment. It is defined as the heat of fusion absorbed by melting 1 short ton (2,000 lb; 0.893 long tons; 0.907 t) of pure ice at 0 °C (32 °F) in 24 hours. It is equivalent to the consumption of one ton of ice per day and originated during the transition from stored natural ice to mechanical refrigeration.