Originating during the transition from stored natural ice to mechanical refrigeration, the term is used in many countries, particularly in North America, to describe the heat-extraction capacity of cooling equipment – whether it be refrigeration or air conditioning.
One ton of refrigerant refers to 12,000 B.T.U.s/hour (British Thermal Units per Hour) of cooling effect.
Example: A condensing unit with a cooling capacity of 60,000 B.T.U.s / hour has the capacity of 5 tons.
In, “What is HVAC and what does it mean?” we describe briefly that the cooling effect you feel from your air conditioner doesn’t come from the freon itself, but rather the effects of heat transfer.
References: Wikipedia contributors. “Ton of refrigeration.” Wikipedia, The Free Encyclopedia. 12Oct12. <http://en.wikipedia.org/wiki/Ton_of_refrigeration>.