The Vapor-Compression Refrigeration Cycle
The four major components, pressure-temperature relationships, saturation, superheat, subcooling, and refrigerant state changes.
- Identify the four major components of the vapor-compression cycle and the role of each
- Describe refrigerant state changes at each point in the cycle
- Explain the pressure-temperature relationship and saturation temperature
- Calculate superheat and subcooling and state normal target values
- Compare TXV and fixed orifice metering devices and their charging methods
Leçon 1
The Four Major Components
The Heart of Every Cooling System
Every air conditioning system, heat pump, and refrigeration unit uses the same basic cycle - the vapor-compression refrigeration cycle. This cycle has exactly four major components, and understanding what each one does is fundamental to HVAC service.
The Four Components
Compressor - The compressor is the pump of the refrigeration system. It takes low-pressure, low-temperature superheated vapor from the suction line and compresses it into high-pressure, high-temperature superheated vapor. The compressor creates the pressure difference that drives the entire cycle.
Condenser - The condenser is the heat rejection component. Hot, high-pressure vapor from the compressor enters the condenser and releases heat to the outdoor air (aided by the condenser fan). As heat is rejected, the refrigerant condenses from vapor to liquid. The refrigerant leaves the condenser as a high-pressure subcooled liquid.
Metering Device - The metering device (TXV or fixed orifice) creates the pressure drop between the high side and low side. As high-pressure liquid passes through the restriction, its pressure and temperature drop dramatically. The refrigerant exits as a low-pressure mixture of liquid and vapor.
Evaporator - The evaporator absorbs heat from the indoor air. Low-pressure liquid refrigerant boils (evaporates) as it absorbs heat from the warm air passing over the coil. The refrigerant leaves the evaporator as a low-pressure superheated vapor and returns to the compressor.
Remember the Cycle
The compressor and condenser are on the high-pressure side. The metering device and evaporator are on the low-pressure side. Heat is absorbed at the evaporator and rejected at the condenser.
The four major components of a vapor-compression system are: compressor, condenser, metering device, and evaporator. The evaporator absorbs heat (cooling the space) and the condenser rejects heat (to outdoors). The compressor drives the cycle by creating the pressure difference.