Vapour compression cycle

The basis of most (more than 95%) air conditioning systems is the “vapour compression cycle”. The media (vapour) is Refrigerant (hydrochlorofluorocarbons – HCFC) which is non-toxic, non-explosive and non-corrosive. These Refrigerants have a boiling point of aprox. Minus 53℃ which means that even if the air (outside or inside) temperature is as low as minus 50℃ it still has heat to be absorbed by refrigerants.

The vapour compression cycle requires four components:

  1. The Compressor: To raise the pressure of low-pressure low temperature gas to high-pressure high temperature gas.
  2. The Condenser: To change the state of high-pressure, high temperature gas to high-pressure, high temperature LIQUID. This is achieved by passing ambient air (known as air-cooled) or water (known as water-cooled) over the condenser tubes.
  3. The Expansion Device: The purpose of the device is to change the state of the refrigerant from high-pressure, high temperature liquid to low pressure low temperature saturated liquid. This is achieved by passing the liquid through an orifice.
  4. The Evaporator: To absorb the heat from room air or water, which in the case of a chiller is circulated around the evaporator coil. This will change the state of low-pressure, low temperature saturated liquid to low pressure, low/medium temperature gas.

These components are common to the vast majority of domestic refrigerators.

This vapour compression cycle if reversed (condenser becomes evaporator and visa versa) can now absorb heat from outside and transfer it to inside, hence saving energy. This is called Reverse Cycle Heat Pump. Energy savings can be as high as 4 to 1 (for every kW input we get 4 kW output).