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EZYAIR Team

11 May 2007

How does a split system air conditioner work?

Split system air conditioners operate on a vapour compression refrigeration cycle. This is a thermodynamic process of refrigerant changing state (from a vapour to a liquid to a vapour again) which enables air conditioners to heat or cool.



Figure above: Condenser = 1, TX Valve = 2, Evaporator = 3, Compressor = 4.

1. Super Heated Vapour
We will start the example just before the compressor (No. 4), on the right hand side, where the refrigerant entering the compressor is a saturated vapour. After it goes through the compressor - it's compressed, so it's pressure and temperature of the saturated vapour goes up and it becomes a super heated vapour.

2. Sub Cooled Liquid
The super heated refrigerant is then forced through the condenser coil (No. 1), which has a fan blowing over the coils. This enables the heat to be released from the refrigerant. This process of cooling the refrigerant through the condenser brings the temperature of the vapour down and it changes state, to a sub cooled liquid.

3. Saturated Liquid
Before this sub cooled liquid reaches the evaporator (No. 3), a component inside the evaporator called the pressure release valve ( or TX valve - No.2) abruptly releases the pressure of the refrigerant. This abrupt pressure loss causes flash evaporation of some of the refrigerant and this brings the temperature of the refrigerant down again. The refrigerant is now a sub cooled, saturated liquid.

4. Saturated Vapour
This saturated liquid travels through the evaporator coil (No. 3). The evaporator fan sucks air over the coil and the refrigerant absorbs the heat from the coil. This causes the temperature of the refrigerant to go up, and the temperature of the air to go down. This heat exchange causes the refrigerant to boil and evaporate into a saturated vapour (keep in mind that R410A boils at minus 48.5 degrees, so it's still super cold).

And the Cycle Continues
The saturated vapour then travels through the refrigerant piping back to the compressor, where the refrigerant (in a vapour state) is compressed into a super heated vapour and the cycle continues.

Post Script
If you are learning about refrigeration for the first time. Please keep in mind that it took a colleague of the author, who has a Ph.D in plasma physics, magnetohydrodynamics & astrophysics around a year to get his head around vapour compression refrigeration... so don't sweat it if it doesn't make sense right now!

If you would like to research more on the matter, please follow the links to the following Wikipedia documents:
Wikipedia - Refrigeration
Wikipedia - Vapour Compression Refrigeration

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