One Ton of cooling is the amount of heat needed to melt 2000 pounds of ice in 24 hours.  

1 Ton = 12,000 BTU/hr = 3.517 Kilowatt = 4.713 Horsepower

History:

Before Willis Carrier invented modern day air conditioning in 1902, people Ice Wagonused to cool buildings in the summertime with ice harvested in wintertime.  Ice was delivered at regular intervals throughout summer and fans would blow air over the blocks to cool the space down.  Ice Delivery companies measured the amount of cooling a space needed in “Tons of Ice”, and this terminology has carried through to today.

In the first half of the 1800’s, a man named Frederick Tudor focused on shipping ice from New England to tropical climates.  He experimented with different insulation materials and built Ice Houses, which reduced the melting loss from 66% to 8%.  This allowed ice for cooling to become big business.  By 1907, around 15 million tons of ice was being harvested.  

As the population grew, sewage and other pollutants entering the water made using natural ice for cooling a health risk.  People started getting sick.  First, the brewing industry complained, followed by the meat packing and dairy industries.  So human ‘POOP’ was one of the main motivations to find an alternate way to keep things cool, and spurned the invention of modern day refrigeration.

Interesting Facts:

The Bank of America building in New York still uses ice for cooling.  They freeze water in gigantic freezers overnight, when the energy costs are lower, and circulate air over the ice during the day to save on air conditioning costs.  The building claims to be the most “green” building in New York.