One ton of refrigeration (TR) is a unit of measurement used in the field of refrigeration and air conditioning to quantify the cooling capacity of a system. It is defined as the amount of cooling required to freeze one short ton (2,000 pounds or approximately 907 kilograms) of water into ice at 0 degrees Celsius (32 degrees Fahrenheit) in 24 hours.
The term "ton" in this context does not refer to weight but rather to a unit of cooling capacity. The idea behind using this unit goes back to the early days of refrigeration when ice was commonly used to cool buildings and store food. One ton of refrigeration is equivalent to absorbing 12,000 British thermal units (BTUs) of heat per hour.
To put it simply, one ton of refrigeration represents the cooling power needed to remove enough heat from a space to freeze one ton of water in a day. Modern refrigeration and air conditioning systems are typically rated in tons, with larger systems having higher tonnage to meet the cooling demands of larger spaces or buildings.