Refrigeration Cycle

The refrigeration cycle, sometimes called a heat pump cycle, is a means of routing heat away from the area you want to cool. This is accomplished by manipulating the pressure of the working refrigerant (air, water, synthetic refrigerants, etc.) through a cycle of compression and expansion.  

Refrigeration, or cooling process, is the removal of unwanted heat from a selected object, substance, or space and its transfer to another object, substance, or space. Removal of heat lowers the temperature and may be accomplished by use of ice, snow, chilled water or mechanical refrigeration.

The 4 main components of refrigeration cycle

• compressor
• condenser
• expansion device (expansion valve)
• evaporator

Compressor

Compression is the first step in the refrigeration cycle, and a compressor is the piece of equipment that increases the pressure of the working gas. Refrigerant enters the compressor as low-pressure, low-temperature gas, and leaves the compressor as a high-pressure, high-temperature gas.

Types of compressors

Compression can be achieved through a number of different mechanical processes, and because of that, several compressor designs are used in HVAC and refrigeration today. Other examples exist, but some popular choices are

• Reciprocating compressors
• Scroll compressors
• Rotary compressors

Condenser

The condenser, or condenser coil, is one of two types of heat exchangers used in a basic refrigeration loop. This component is supplied with high-temperature high-pressure, vaporized refrigerant coming off the compressor. The condenser removes heat from the hot refrigerant vapor gas vapor until it condenses into a saturated liquid state, a.k.a. condensation. After condensing, the refrigerant is a high-pressure, low-temperature liquid, at which point it’s routed to the loop’s expansion device.

Expansion Device (expansion valve)

These components come in a few different designs. Popular configurations include fixed orifices, thermostatic expansion valves (TXV) or thermal expansion valves (pictured above), and the more advanced electronic expansion valves (EEVs). But regardless of configuration, the job of a system’s expansion device is the same - create a drop in pressure after the refrigerant leaves the condenser. This pressure drop will cause some of that refrigerant to quickly boil, creating a two-phase mixture.  

This rapid phase change is called flashing, and it helps tee up the next piece of equipment in the circuit, the evaporator, to perform its intended function.

Evaporator

The evaporator is the second heat exchanger in a standard refrigeration circuit, and like the condenser, it’s named for its basic function. It serves as the “business end” of a refrigeration cycle, given that it does what we expect air conditioning to do – absorb heat.

This happens when refrigerant enters the evaporator as a low temperature liquid at low pressure, and a fan forces air across the evaporator’s fins, cooling the air by absorbing the heat from the space in question into the refrigerant.