Air-Conditioning Equipment:Liquid Refrigerant Control Devices

Liquid Refrigerant Control Devices

Each refrigeration system may be described in terms of a low side and a high side of operating pressure. The low side is that part of the refrigeration system that normally operates under low pressure (as opposed to the high side). It is identified as that part of a refrigeration system lying between the expansion valve and the intake valve in the compressor, and includes the evaporating or cooling surface, the intake line, and the compressor crankcase—in other words, that part of the refrigeration equipment under intake pressure. The term low side is sometimes used to designate the evaporator coils.

The high side is that part of the refrigeration system operating under high pressure. The term high side is sometimes used to designate the condensing unit.

Some form of expansion device is necessary to control the flow of liquid refrigerant between the low and high sides of a refrigeration system. The following expansion devices are designed to pro- vide automatic control of refrigerant flow:

1. Automatic expansion valves

2. Thermostatic expansion valves

3. Float valves

4. Capillary tubes

Automatic Expansion Valves

An automatic expansion valve is a pressure-actuated diaphragm valve used to maintain a constant pressure in the evaporator of a direct-expansion mechanical refrigeration system (see Figure 9-22). It accomplishes this function by regulating the flow of refrigerant from the liquid line into the evaporator. In this way, the evaporator is always supplied with the proper amount of refrigerant to meet conditions. An automatic expansion valve does not respond well to load fluctuations. For this reason, it is not recommended for use in air-conditioning (see Thermostatic Expansion Valves).