Tons of Cooling

Tons of Cooling….

Instructor: How much is a ton of refrigeration?

Student: Oh, about 2,000 pounds.

Air conditioning systems are usually rated in tons instead of BTU/hour. Newcomers to HVAC often have difficulty understanding why a unit of weight is used to specify the cooling capacity of AC units. The origin is from the days of cooling with ice and a term named Ice Melting Equivalent, or IME. Here is the explanation:

…At the meeting of the American Society of Mechanical Engineers, a committee appointed by that society to suggest a standard tonnage basics for refrigeration proposed as a unit for measuring, cooling effect, the equivalent of the heat required to melt one pound of ice, i.e.,144 Btu. The unit for a ton of ice-melting capacity was then fixed at 228,000 BTU, which, since the rating is always expressed in tons per 24 hours, makes a ton duty equivalent to the rate of 12,000 BTU per hour, or 200 BTU per minute.

Therefore, if each ton of cooling effect is equal to 12,000 BTU/hour, a 3 ton air conditioning system would have a capacity of 3 x 12,000 BTU/hour, or 36,000 BTU/hour.