A Ton of Refrigeration (TR) is a unit of power used in refrigeration and air conditioning. It is defined as the amount of heat absorbed to freeze one ton (2000 pounds) of water at 0°C in 24 hours. In SI units, 1 TR equals 3.517 kW.
The term "ton of refrigeration" originated in the 19th century. Early refrigerating machines were designed to mimic the cooling effect of ice. The ton was a convenient measure, reflecting the amount of ice that could be produced or melted in a day. The concept became standardized in engineering and HVAC (heating, ventilation, and air conditioning) fields.
TR is widely used in the HVAC industry to describe the cooling capacity of air conditioning units and refrigeration systems. It is prevalent in commercial and residential settings, particularly in North America.