Introduction
Refrigeration means cooling a space to a temperature lower than the ambient temperature. Refrigeration capacity is defined as the rate of heat removal from space and it is expressed in terms of TR (Tons of Refrigeration). It is also known as cooling capacity.
One TR is the rate of heat transfer needed to transform 1 ton of liquid water at 0°C to 1 ton of ice at 0°C within 24 hours as per the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE).
Calculation of 1 Ton of Refrigeration
Q =m L
Where
Q = amount of heat removal required for transforming 1 ton of water to 1 ton of ice at 0°C.
M = Mass of ice or water (1 ton is considered as 1 US ton Since the definition is given by ASHRAE, 1 US ton= 907 Kg)
L= Latent heat of fusion of ice is 334.21 kJ/kg (Since only phase changes is involved)
Now, the rate of heat removal per day in transforming water to ice is,
Why refrigeration capacity is expressed in Tons?
Before the invention of mechanical refrigeration (i.e., Vapour Compression Refrigeration Cycle VCRS) people from North American countries, Norway & Canada used to trade ice collected from icy freshwater lakes and ponds (called natural ice trade) to South American countries and Southern US states during summer months. Ice was kept near the fan to cool the houses. The ice trucks supply the ice in terms of Tons and the truck visits once in every 24 Hrs.
The transition from horses to steam engine led to the birth of the horsepower unit similarly, the natural ice trade led to the birth of TR (Tons of Refrigeration).