Heat

Heat is a form of energy. The unit of heat most used in refrigeration work is british thermal unit (Btu). The british thermal unit (Btu) is the amount of heat required to raise the temperature of one pound of water one degree Farenheit. In refrigeration work, the temperatures between 63 and 64 F are used. In some scientific work, the temperaure of maximum density of water is ued, which is 30 to 40 F. The difference in the values taken at these two different temperatures is insignificnt.

If  a substance is cooled and heat is removed, the amount of heat removed is calculated in the same way. That is,if heat is removed from water, the temperature difference multiplied by the number of pounds of water gives the number of Btu  removed in cooling the water.

In engineering work which involves large heat loads, the unit therm, wich equals 100,000 Btu, is often used.

Example : how much heat will be required to raise the temperature of 62.4 lb. (1 cu.ft) of wter from 40 F.to 80 F ?.

Btu         = wt. x degree change

                = 62.4 x (80 – 40)

                = 62.4 x 40

                = 2496 Btu