How Air Conditioning Works

Air conditioning essentially requires a warm surface, a cold surface and a fan and relies on the behaviour of a “refrigerant” – a chemical which is transformed easily from a gas to a liquid and vice versa – for its operation. It is the refrigerant that is used to transport heat from the air inside your home to the outside. A device known as a compressor pumps refrigerant through two coils, one of which becomes hot, and the other cold. Warm air from a room is blown over the cold coil, which not only cools but dehumidifies – that is condenses the water vapour from – the air leaving it cool and refreshing. Some warm air over the hot coil, draws heat away from it and is exhausted through a window or a vent in an external wall.

Air Conditioning Units

A typical air conditioning system is composed of a compressor, a condenser which is usually located outside a building, and an evaporator located inside. The compressor and condenser unit contains a long cylindrical coil, a fan to blow air through the coil, and metal fins, which allow heat to dissipate quickly from the condenser. Gaseous refrigerant at low pressure is squeezed or “compressed” by the compressor so that its energy and temperature rises. Hot high pressure gas flows into the condenser where it is cooled and becomes a liquid although still under high pressure.

The cold side of an air conditioning system, the evaporator, is often part of a furnace inside a building and receives the refrigerant liquid through a very small orifice. The pressure of the liquid drops and it starts to become gas once again. This process of evaporation is accompanied by cooling of the surrounding air as its heat energy is used to force the molecules of refrigerant apart and the evaporator, again has metal fins to promote heat exchange. A fan connected to the evaporator circulates warm air from the interior of a room across the fins. Cool low pressure gas is returned to the compressor and the cycle is repeated.

This so-called “split” system – the hot side of an air conditioning system outside and the cold side indoors – is considered to be the most cost-effective approach to air conditioning allowing larger condenser and compressor units and reducing the amount of noise generated inside a building. Fundamentally, however, there is very little difference between a split system and a portable, or window, air conditioning system. Refrigerant lines between the evaporator and condenser units can be passed through a hole in an external wall and the condenser unit itself can be placed on the ground or a flat roof or hooked onto a window frame.