What is a “Ton” of Air Conditioning?

Have you ever wondered what a “Ton” of air conditioning refers to?

Before the invention of refrigeration air conditioning, cooling was done with big block of ice and a fan.
When cooling machines were invented, the capacity was rated based on the equivalent amount of ice melted in a day (24 hour period).

A Ton of cooling is now defined as delivering 12,000 British Thermal Units (BTUs) per hour of refrigeration effect. A BTU is a unit measurement of energy. One BTU (British thermal unit) is measured by one pound of water, changing one degree Fahrenheit. There are 12,000 BTU’s in one Ton of refrigeration effect. This is how mechanical air conditioning units came to be measured in “tons” of cooling capacity. Interestingly, BTUs are not commonly used in Britain today. BTUs are most commonly used in the United States.

For reference, a window air conditioner capacity is most often less than one ton of cooling effect usually in the 9000-12,000 BTU Range (3/4 – 1 Ton). The capacity of central air conditioning units in our homes varies by location but generally ranges from 2 tons to 5 tons. Commercial buildings use larger units due to extra heat loads not seen in homes.

Here in Tucson A/C units are mostly used  for cooling, but in other climates A/C units are also used to remove moisture from indoor air and are sized accordingly (think drain tubes dripping during the high humidity of the Monsoon season!). In Florida, for example, A/C units are commonly used to remove moisture from the air and are usually sized at 3 tons of refrigeration effect.

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