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.

Pressure-Temperature Relationships, Gases

One of the basic fundamentals of thermodynamics is called the "perfect gas law." This describes the relationship of the three basic factors controlling the behavior of a gas--pressure, volume, and temperature. For all practical purposes, air and highly superheated refrigerant gases may be considered perfect gases, and their behavior follows the following relation:

Pressure x Volume/Temperature = Pressure x Volume/Temperature

Although the "perfect gas" relationship is not exact, it provides a basis for approximating the effect on a gas of a change in one of the three factors. In this relation, both pressure and temperature must be expressed in absolute values, pressure in psia, and temperature in degrees Rankine or degrees Fahrenheit above absolute zero. (degrees F. plus 460 degrees). Although not used in practical refrigeration work, the perfect gas relation is valuable for scientific calculations and is helpful in understanding the performance of a gas.

One of the problems of refrigeration is disposing of the heat which has been absorbed during the cooling process, and a practical solution is achieved by raising the pressure of the gas so that the saturation or condensing temperature will be sufficiently above the temperature of the available cooling medium (air or water) to insure efficient heat transfer. When the low pressure gas with its low saturation temperature is drawn into the cylinder of a compressor, the volume of the gas is reduced by the stroke of the compressor piston, and the vapor is discharged as a high pressure gas, readily condensed because of its high saturation temperature.

Katey Werner