Refrigeration systems are basically designed to remove heat energy from the product to be refrigerated. The removal of this heat energy reduces the product to a safe temperature for either long- or short-term storage. This heat energy is not destroyed, but is rather transferred from the product to an area where it does not matter such as the outside air or a water source. In its simplest form, the first law of thermodynamics states that energy can neither be created nor destroyed. The amount of energy in the universe is constant — energy can be changed, moved, controlled, stored, or dissipated. This is one of the major operating principles behind the refrigeration systems used today.

The amount of heat energy a system can transfer is its refrigeration capacity. One of the ways a system’s capacity is rated is in tons of refrigeration (sometimes abbreviated as TR). When referring to a system’s capacity, most technicians define a ton of refrigeration as 12,000 Btu per hour. It is the “per hour” that is important to remember when discussing a ton of refrigeration. A ton of refrigeration can also be stated as the heat transfer of 288,000 Btu per 24 hours, or 200 Btu per minute.

## Language of Origin?

So, where did the term tons of refrigeration originate?

The roots of refrigeration are in the ice making industry, and ice manufacturers wanted an easy way of understanding refrigeration system sizing in terms of the production of ice. Using the latent heat produced from the fusion of pure water, ice manufacturers were able to develop a method of rating the size of a refrigeration system.

The latent heat of fusion of pure water is 144 Btu per pound. So, it requires the removal of 144 Btu per pound to transform one pound of pure water at 32°F into one pound of pure ice at 32°. Ice manufacturers used this information to determine how much heat energy must be removed from one short ton (2,000 pounds) of pure water at 32° to cause it to produce one short ton of ice at 32° in a 24-hour period.

If it requires the removal of 144 Btu from one pound of pure water at 32° to produce one pound of ice, it will require 288,000 Btu to be removed from one ton of water to produce one ton of ice, again over a 24-hour period, so that’s 144 Btu per pound x 2,000 pounds = 288,000 Btu.

So, a ton of refrigeration can be defined as the amount of heat removal to produce one ton of ice at 32° from one ton of water at 32°.

Now, dividing 288,000 Btu per 24 hours by 24 will equal the same heat removal of 12,000 Btuh as the requirement to produce one ton of ice in one day. Dividing 12,000 Btu per hour by 60 minutes yields 200 Btu per minute, which is also a ton of refrigeration. The transfer of 288,000 Btu per 24 hours, 12,000 Btuh, and 200 Btu per minute all equal one ton of refrigeration.

Publication date: 8/4/2014