The Process of Refrigeration in HVAC: Air Conditioning and Heat Pumps
The process of refrigeration uses the vapor-compression cycle to move heat from one place to another. In many HVAC air conditioning and heat pump applications the process of refrigeration or the vapor-compression cycle is what makes it work. This process, in the air conditioning mode, moves heat from inside the structure to the outside. Heat pumps draw heat from the outside even when it is cold and move the heat inside using the vapor-compression cycle or refrigeration. Heats pumps by the way, heat in the winter and cool in the summer but it uses the refrigeration process to accomplish the heating and cooling. The process of refrigeration or vapor-compression cycle in HVAC air conditioning and heat pump applications is a mechanical and chemical process of moving heat from one place where it is not wanted or needed and moving it to another place.
Major Components in HVAC Air Conditioning and Heat Pumps
In a typical HVAC air conditioner or heat pump there are four major components that make the process of refrigeration work. These HVAC components are:
1. HVAC Refrigeration Compressor - The HVAC refrigeration compressor receives the refrigerant vapor from the evaporator coil and compresses the refrigerant vapor. The vapor enters the refrigeration compressor at a low pressure and a low temperature and leaves the refrigeration compressor at a higher temperature and a higher pressure. The lower temperature refrigerant vapor is responsible for providing cooling for the refrigeration compressor and it also carries with it a small amount of oil which migrates from the compressor throughout the system. After the refrigerant vapor is compressed it is discharged to the condenser coil.
2. HVAC Condenser Coil - The condenser coil receives the high pressure high temperature refrigeration vapor from the compressor and immediately begins to remove heat from the refrigerant vapor. As the refrigerant vapor makes its way through the condenser coil more and more heat is removed and the refrigerant vapor changes state from a refrigerant vapor to a refrigerant liquid. While the liquid refrigerant changes temperatures from a higher temperature to a slightly lower temperature the pressure remains constant. As the refrigerant vapor leaves the condenser coil it makes it way to the metering device.
3. HVAC Metering Device - depending on the type of HVAC air conditioning or heat pump system it is and the efficiency range of the system will depend on the type of metering device the system has installed by the HVAC manufacturer of the air conditioner or heat pump system. Lower efficiency HVAC air conditioner and heat pump models have fixed orifice metering devices while higher efficiency systems have thermostatic expansion valves installed in the HVAC air conditioner or heat pump system. The thermostatic expansion valve is far more complex than the fixed orifice metering device as the thermostatic metering device modulates the refrigerant flow based on the temperature of the refrigerant temperature in the evaporator coil. This allows a specific amount of refrigerant, based on demand, to be metered into the evaporator coil while the fixed orifice metering device allows the same amount of refrigerant to enter the enter the coil no matter the conditions or the demand. As the liquid refrigerant enters the metering device it changes temperature and pressure. A partial amount of the liquid refrigerant flashes into a refrigerant gas or vapor as it leaves the metering device and enters the evaporator coil.
4. HVAC Evaporator Coil - the evaporator coil is responsible for absorbing heat into the coils and the refrigerant. This is usually done as result of passing air or water over the evaporator coil where a heat exchange process takes place. Heat leaves the air or water (whatever medium is used) and is absorbed into the coil and the liquid refrigerant. As more and more heat is absorbed by the evaporator coil and the refrigerant the refrigerant again changes state from a liquid to a refrigerant vapor. By the time the refrigerant leaves the evaporator coil the refrigerant should be all vapor and ready to be received again by the refrigeration compressor.
The HVAC air conditioning and heat pump refrigeration process is simply a matter of moving heat from one place to another. In moving this heat it either provides heating (for a heat pump in the winter) or provides cooling (for a heat pump and an air conditioner in the summer). There are many technical considerations for this process to work as efficiently as possible such as the proper amount of airflow or water flow across the evaporator and/or a properly charged HVAC air conditioning and heat pump system. For forced air systems a good tight ductwork system also helps efficiency as well as ensures that the conditioned air gets to its designated area. The process of refrigeration in HVAC works at maintaining comfortable temperatures for many different applications in HVAC.
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