M-4
3/2002
REFRIGERATION OPERATION
The refrigeration operation section is divided into three areas: Basic Refrigeration
Principle, Detailed Vending Machine Refrigeration Cycle, and Parts Description.
BASIC REFRIGERATION PRINCIPLE
What a refrigeration system really accomplishes is the transfer of heat. A refrigeration
system removes the excess heat from a refrigerated area and then transfers it to a
condenser where it is dissipated. As heat is removed, the refrigerated area cools.
In vending machines, large quantities of the heat must be transferred rapidly, economically
and efficiently. This process must be able to withstand continuous repetition, without loss
of refrigerant, over an extended period. The most common system used in the vending
industry is the vapor compression (or simple compression) cycle system. It consists of
four basic elements: An evaporator, a compressor, a condenser, and a pressure-reducing
device (all part of a sealed system).
The compression system operates at two pressure levels: The low evaporating pressure
and the high condensing pressure. The refrigerant acts as the transport medium, in which
heat is moved from the evaporator to the condenser; at the condenser, the heat is
dissipated into the surrounding air.
The liquid refrigerant changes from a liquid to a vapor and back to a liquid again. This
change of state allows the refrigerant to absorb, and rapidly discharge, large quantities of
heat efficiently.
BASIC VAPOR COMPRESSION SYSTEM CYCLE:
In the evaporator the liquid refrigerant vaporiz
es. This change occurs at a temperature low
enough to absorb heat from the refrigerated space. The temperature of vaporization is
controlled by the pressure maintained in the evaporator (the higher the pressure, the
higher the vaporization point).
The compressor pumps the vapor from the evapor
ator, through the suction line, and to the
condenser. The compressor takes the low pressure vapor and compresses it, increasing
both the pressure and the temperature. The compressor pumps the vapor at a rate rapid
enough to maintain the ideal pressure. The hot high pressure vapor is forced out of the
compressor, into the discharge line and then into the condenser.
Air is blown through the condenser, allowing heat to transfer from the condenser and into
the passing air. As the heat is removed, the stored refrigerant is condensed into a liquid.
The liquid refrigerant is stored in the lower t
ube of the condenser. This is where it flows
through the capillary tube back into the evaporator, where the refrigeration cycle is
repeated.
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