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Getting an Airconditioner - The Basics

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Getting an Airconditioner - The Basics

So summer is here and you need an airconditioner. But its not as easy as going to a shop and picking one up. You need to know what size and type to get, to best suit your home, and the number and size of the rooms you want to cool.

An air conditioner's ability to cool a room, or cooling output is measured in kilowatts (kW) which should be labelled on the unit. This is important, as it will determine the size of air conditioner you buy. The other part of the equation is the size of the room you need to cool. If you buy a small airconditioner it may not cool a large room adequetely; and if you buy a large one, it will waste electricity and malfunction.

A heat load calculation will determine the size of air conditioner for the size of the room.

As an approximate guide for sizing a room is:

125watts (0.125kW) per square metre of floor area to be cooled in living areas;

80 watts (0.080kW) per square metre of floor area in bedrooms.

These estimates depend on the climate and the efficiency of your house design (orientation, glazing and insulation levels).

The best way however to get an accurate heat load calculation is to get a licensed contractor to perform a detailed calculation in your home. A calculation needs to be performed, not just a visual estimate. Below is a list of things to remember and ask your contractor, as the size of the room or house alone is only a small part of the heat load calculation.

- Orientation, windows, building materials, the number of people in the house, insulation and geographic location play an important part.

- Windows and the direction they face can make a huge difference to the amount of heat that enters your house, so it's important to make sure that your contractor has measured the windows and noted the direction they face.

- Air does not turn corners or travel up stairs on its own - a ducted system or multiple indoor units will be required to cool multiple rooms.

- If the system is to be zoned, make sure you ask the contractor how the zoning will function - it's not necessarily a case of the more zones the better the system.

Usually, a zoned system will only have the capacity to cool one or two zones at a time - the living areas during the day, and bedrooms at night, for example. If the system can cool the entire house at once (and this is what you want) you may not need zoning.

Make sure you ask your contractor for a copy of the heat load calculation they have performed. Ask your contractor to provide a written guarantee of the temperature that the system will achieve inside at a given outdoor temperature (26°C inside when it is 35°C outside, for example)

Other factors which will influence your decision on which kind of air conditioner to buy include location, orientation, external and internal shading, insulation and sealing. All these factors are part of the building envelope, and contribute to the design of the house and its passive heating and cooling ability.

Location is important in terms of the climate your house is situated in. Climate is not only limited to temperature, but includes humidity. Orientation of the rooms of the house will dictate how much power is needed to cool them. Rooms which face north, east or west will receive more warmth from the sun and use more energy to cool them. Linked to this is shading from the sun with blinds or curtains internally, and with eaves or canopies outside. Finally insulation in the roof and walls will reduce the susceptibility to variation in outside temperatures. This will not only keep the heat out, but keep the cool air from the air conditioner inside. The same applies with sealing, as cracks under doors and windows will break the seal and let warm air into the house and let the cool air out.

Once you have assessed the area you need to cool, you will be prepared to make an easier decision about which air conditioner you need. The main types of air conditioners are split system, multi-split system, ducted system and evaporative system.

A split system is an air conditioner which has two separate units making up the system - an indoor unit (evaporator), which is located inside the space being cooled, and an outdoor unit (condenser) where the heat from inside is rejected. The two units are connected by pipes which carry refrigerant.

A variation on the standard split system is the multi-split system, which as multiple indoor units connected to a single outdoor unit. This allows the system to cool multiple rooms.

A ducted system is one that provides cooling to multiple rooms through a series of ducts, which are usually installed in the roof.

An evaporative system provides cooling by drawing air across a series of wetted “pads.” Water on the pads evaporates as the air flows over it, cooling and humidifying the air. Evaporative systems are sometimes also referred to as a “swamp cooler.” Evaporative systems tend to use less energy than split or ducted systems, however, unlike split or ducted systems they consume water to provide cooling.

Note that because they rely on evaporation to function, evaporative systems can only be used in some parts of Australia - they are not appropriate in areas which experience high humidity (costal regions in Queensland, for example), as the air already has very high moisture content. Ask your licensed contractor if evaporative cooling is suitable for your area.

You will also need to make sure you leave some windows open to allow air to flow in and out of the house, otherwise it is possible for condensation to form inside the house as a result of the elevated indoor humidity.

Air conditioners are not appliances that you can install yourself - most will require the connection of refrigerant pipelines as well as electrical and plumbing work. By law, only licensed and qualified contractors are allowed to connect refrigerant pipelines.

So always ensure that you use a contractor licensed by the Australian Refrigeration Council (ARC). By law, all installers are required to hold an ARC license, visit for more information on the licensing scheme.

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