How Air Conditioning Works

Last Updated on Tuesday, 20 April 2010 11:39 Written by Richard Saturday, 01 March 2008 14:37

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Process of Rejecting Heat (Refrigeration)

How an Air Conditioner Works

How does an air conditioner work? The simple explanation of an HVAC air conditioning unit is it is a system that removes heat from a space where there is a desire to keep that space cool. In human terms the air conditioning system cools but in scientific terms the air conditioner removes heat. To truly understand how the air conditioner works we must look at it in scientific terms. Cold or cool, in scientific terms does not begin until the temperature drops below -459 degrees Fahrenheit. That is considered absolute zero and any temperature above -459 degrees Fahrenheit is considered to have a measurable quantity of heat. So even at 0 degrees Fahrenheit there is measurable heat. Most humans would be uncomfortable at that temperature but the point is that an air conditioning unit uses a mechanical process to remove heat from the air and make the temperature comfortable within human comfort ranges. How the HVAC air conditioning systems works is not how many people think the air conditioner works. The mystery of how an air conditioning system works is no longer a mystery for you. So, read more to find out how an air conditioner works?

How an Air Conditioner Works

The simple explanation of an air conditioning unit is it is a system that removes heat from a space where there is a desire to keep that space cool. In human terms the air conditioning system cools but in scientific terms the air conditioner removes heat. To truly understand how the air conditioner works we must look at it in scientific terms. Cold or cool, in scientific terms does not begin until the temperature drops below -459 degrees Fahrenheit. That is considered absolute zero and any temperature above -459 degrees Fahrenheit is considered to have a measurable quantity of heat. So even at 0 degrees Fahrenheit there is measurable heat. Most humans would be uncomfortable at that temperature but the point is that an air conditioning unit uses a mechanical process to remove heat from the air and make the temperature comfortable within human comfort ranges.

The Air Conditioner Refrigeration Cycle

We begin this process at the return duct where filters are typically changed and usually the thermostat is installed (most thermostats are installed close to the return duct in a forced air system). The thermostat calls for the air conditioner to come on. The compressor, condenser fan motor and the blower turn on. The HVAC blower inside the air handler kicks on and begins pulling air towards the return. The air is channeled towards the air handler through the return ducts. Depending on the configuration of the HVAC air conditioning system, the air is sucked into the blower and pushed through the air handler towards the air conditioner evaporator coil. As the air passes over the evaporator some of the heat contained in the air (HVAC chillers use water for the medium instead of air) is absorbed into it. The refrigerant inside the evaporator coil, originating from the HVAC condenser, has been metered causing a pressure drop of the refrigerant. The process of the metering of the refrigerant and resulting pressure drop causes the temperature of the refrigerant to drop. This causes the evaporator to be cooler than the air. As more warmer air passes over the evaporator coil the heat from the air is absorbed into the coil and refrigerant, which is partially a liquid. This heat transfer, from the air, to the coils, to the refrigerant, causes the refrigerant to boil and turn into a vapor.

The vapor leaves the evaporator coil and is pulled towards the compressor. The vapor enters the HVAC compressor where it is compressed. This compression process raises the temperature and pressure of the refrigerant where it is discharged into the condenser coils. Again using air (some systems use water) being pulled through the coils, another heat exchange process occurs. This time the heat picked up from the evaporator coils is rejected to the outside air. As the temperature of the refrigerant drops it once again becomes a liquid and is pumped back towards the metering device usually located near the evaporator coils where it will begin the process of absorbing heat from the evaporator all over again.

And in case you were wondering, a heat pump works in quite the same fashion except it pulls the heat out of the outside air (or the water source if you have a geothermal heat pump) and moves it inside. For more information on this read our heat pump articles to find out how a heat pump works.

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