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REFRIGERATION BASICS
Modern refrigeration has many applications. The first, and probably the most important, is the
preservation of food because most foods kept at room temperature spoil rapidly. However, when kept
cold most foods will keep much longer.
Before looking at the operation of mechanical refrigeration, it is important to understand the physical and
thermal properties of the mechanisms and substances used to extract heat. Removing heat from the
inside of the walk-in is somewhat like removing water from a leaking boat. A sponge may be used to
soak up the water and then held over the side, squeezed, and the water released overboard. The
operation may be repeated as often as necessary to transfer the water from the boat back into the lake.
In a walk-in, heat instead of water is transferred. Inside the walk-in heat is absorbed by the liquid
refrigerant in the evaporator as the refrigerant changes from a liquid to a vapor. After the refrigerant has
absorbed heat and turned it into a vapor, it is pumped into the condensing unit located outside the
refrigerated space and then compressed. The heat is "squeezed" out by high temperature and then
cooled in the condenser. This cycle repeats until the desired temperature is obtained.
Cold is a relative term used to describe low temperature, it is not something that is produced. Rather, the
removal of heat results in a condition termed “cold”. A refrigerator produces a condition called "cold" by
removing heat from inside the refrigerator and the stored content within it. You have probably felt the
heat on the floor as you walked by your refrigerator in your home. The principle of heat removal is the
same for your walk-in cooler and/or freezer.
The fact that bacteria are present in most foods calls for it to be preserved in some fashion. Exposing the
food to cold or low temperatures slows the growth of these bacteria preventing foods from spoiling as
quickly. A cooler temperature slows the activity of all organisms, thus the growth of bacteria on
refrigerated food slows dramatically.
The spoiling of food is actually the growth of bacteria. If the bacteria can be kept from increasing, the
food will remain edible for a longer period of time. Since most foods contain a considerable amount of
water, the food must be kept slightly above freezing temperatures.
If food is frozen slowly, at or near the freezing point of water, large ice crystals will form and break down
the food tissues. When such food defrosts, it spoils rapidly and the taste and appearance of the food is
greatly compromised. To prevent this problem fast freezing at temperatures between 0° F to -15° F is
recommended. By using these low temperatures small crystals form which do not injure the food tissues.
It is always important to keep in mind the difference between refrigerating and freezing. Further, the
standard walk-in cooler is designed to maintain the temperature of the product at 35° F, providing the
temperature of the product is within 10° F of this temperature. If the product to be maintained is
continually at a higher temperature, additional refrigeration system capacity will probably be required.
The same parameters hold true for freezers.
To insure you have adequate refrigeration capacity, be sure to provide your sales consultant with as
much information as possible about how you intend to use your cooler and/or freezer.
HEAT LOAD
As we mentioned earlier, the refrigeration system on your walk-in does not make things cold. The system
instead removes heat from the walk-in structure. Where does the heat come from that must be removed
by the refrigeration process? The two most common sources you can control are door openings and
product load. Did you know that one 100-watt lamp left on in a walk-in would generate 8,208 BTU in a
24-hour period? Keep door openings and closings to a minimum to conserve energy. When working
inside the walk-in, close the door behind you. No need to worry, as there is a door opener inside.
