Walk-in coolers or freezers are a type of refrigeration devices that are big enough for people to enter into and store meat and other food items. Groceries and restaurants are utilizing these units for storing by bulk.

Refrigeration is a branch of mechanical engineering concerned with providing a means of inducing heat flow away from objects or spaces which it is desired to maintain at temperatures lower than their surroundings. By definition, heat is energy in transition as a result of temperature difference. Hence, to achieve refrigeration it is necessary to provide a heat "sink" and maintain it at a temperature lower than its surroundings. So far, the greatest amount of refrigeration is obtained through mechanical or chemical means. Essentially, all mechanical refrigeration systems are thermal pumps.

The simple vapor cycle of mechanical refrigeration is carried out in four mechanisms connected to form a closed refrigerant circuit compressor, condenser, expansion valve, and evaporator or cooler.

For businesses where the refrigeration effect is needed only intermittently, a widely used method of reducing the first and operating costs of the installation is to size the compressor for continuous operation, providing a means of storing the refrigeration for withdrawal at the required rate during brief intervals when the load exists. A dairy, for example, may require a cooling effect at a 4-ton rate for two 3-hr. periods per day. This load could be handled by installing a 4-ton machine, but the electrical-demand charge for such a unit would make the operation cost high and its size would be responsible for a substantial first cost.

If a 1-ton compressor would be installed and operated continuously, the quantity of cooling made available by it during each 24-hr. period would be exactly the same as that provided by the 4-ton unit when operated for a total of 6 hrs out of 24. The first cost of the smaller compressor would of course be less, but this saving would be at least partially offset by the added cost of such refrigeration-storage equipment as might be required. Neglecting losses, the operating cost would be less for the smaller compressor because of the great reduction in the utilities-demand charge.

Various methods have been used for storing refrigeration. In some cases tanks of brine or water are reduced in temperature during the non-use period and then allowed to gain a substantial temperature increment during the brief periods when the refrigeration is required.

These commercial refrigeration systems are very invaluable for businesses that require food to be stored for future use. Because of these devices, a lot of time and effort have been conserved.