Nova Kool Manufacturing ULC

Basic Refrigeration Principles

Most users normally associate refrigeration with cold and cooling, yet the practice of refrigeration engineering deals almost entirely with the transfer of heat. This seeming paradox is one of the most fundamental concepts that must be grasped to understand the workings of a refrigeration system.

Cold is really only the absence of heat, just as darkness is the absence of light, and dryness is the absence of moisture.

Change of State

Most common substances can exist as a solid, a liquid, or a vapor, depending on their temperature and the pressure to which they are exposed. Heat can change their temperature, and also can change their state. Heat is absorbed even though no temperature change takes place when a solid changes to a liquid, or when a liquid changes to a vapor. The same amount of heat is given off when the vapor changes back to a liquid, and when the liquid is changed to a solid.

The most common example of this process is water, which exists as a liquid, can exist in solid form as ice, and exists as a gas when it becomes steam. As ice it is a usable form of refrigeration, absorbing heat as it melts at a constant temperature of 32° F. If placed on a hot stove in an open pan, its temperature will rise to the boiling point (212° F. at sea level). Regardless of the amount of heat applied, the temperature cannot be raised above 212° F. because the water will completely vaporize into steam. If this steam could be enclosed in a container and more heat applied, then the temperature could again be raised. Obviously the boiling or evaporating process was absorbing heat.

When steam condenses back into water it gives off exactly the same amount of heat that it absorbed evaporating. (The steam radiator is a common usage of this source of heat.) If the water is to be frozen into ice, the same amount of heat that is absorbed in melting must be extracted by some refrigeration process to cause the freezing action.

The question arises: Just where did those heat units go? Scientists have found that all matter is made up of molecules, infinitesimally small building blocks which are arranged in certain patterns to form different substances. In a solid or liquid, the molecules are very close together. In a vapor the molecules are much farther apart and move about much more freely. The heat energy that was absorbed by the water became molecular energy, and as a result the molecules rearranged themselves, changing the ice into water, and the water into steam. When the steam condenses back into water, that same molecular energy is again converted into heat energy.

Katey Werner