Cooling Systems

Cooling Systems

The basics of air conditioners

The function of an air conditioner is to change air temperature and humidity. Without exception, the underlying method of operation depends on one fundamental principle of physics - heat exchange. To achieve this there are two commonly used methods:


Water is sprayed over some form of grid. Warm air is then fan-forced through pipes or ducting across the grid. Heat is drawn from the air as water evaporates and cooler air is then fan-forced back into the building through pipes and ducting.

This effect is easily demonstrated: wet your arm and hold it in front of a fan. Body heat is sufficient to warm the thin water layer that will evaporate, and as air blows across the surface your arm will feel cooler. Evaporative air conditioning will normally be used in a cooling system.


A refrigerative air conditioning system is a closed circuit of gas that changes state to a liquid as pressure increases and decreases. When pressure is rapidly released through a special valve, refrigerant liquid returns to a gaseous state and releases heat energy. You can see this effect if you fill a gas cylinder then crack the top. The sudden pressure release results in frosting around the discharge site.

A refrigerative system uses a series of pipes to circulate gas through a loop. This gas returns to the liquid state as it absorbs heat, and then dissipates using a heat sink similar to the metal fins visible behind your refrigerator at home. Refrigerative systems can be reversed to produce warm air; this is called a reverse-cycle system.

Air conditioners consume energy. The system you choose for your home will depend on the volume of air you intend to manage (be it a small room or your entire house), the thermal properties of your house (insulation) and the general climatic conditions of your location. These and other factors will directly impact the efficiency of your system toward achieving the conditions you are seeking.

Low-cost domestic units will operate with relatively little maintenance for 5 to 10 years, depending on the quality of construction. After this time failures will begin to occur such as motor seizure, compressor seizure due to worn components, or a gas leak if pipes become corroded or are subjected to excessive vibration because of faulty installation. They are not generally cost-effective to repair, and newer units are always improving in efficiency.

More sophisticated systems will still require the basic components of compressor, gas circuit, heat sink and pressure release valve. They may include extra components such as a humidifier to ensure the air is not too dry and electronic controls of varying sophistication. The basic components will not change no matter how sophisticated the controls are, or how complex the system is.

Before purchasing, have a qualified air conditioning contractor make the appropriate measurements and calculations for choosing the most appropriate unit for your needs.

By Ian Loft