Central Systems

These may be ducted, or chilled water, fan coil types. With a ducted system, conditioned air is distributed throughout the house, being directed into separate rooms through unobtrusive diffusers located in the ceiling or floor. It is returned through grilles in doors, or along the hallway or corridor to the main return air grille. As it is common practice to locate the equipment and the ducts in the ceiling space, a pitched roof is ideal for installations in new or existing homes.

For homes with flat roofs, the roof-line may be raised to create space for the ducts. Alternatively, underfloor ducts distributing conditioned air through floor registers can be used, provided the floor is not slab on ground.

The ceiling in the hall-entrance area could be dropped to form a plenum, distributing conditioned air through wall registers, or the ducts may be run on top of the roof. Ducted systems can be divided into two types.

Whole house systems

"Whole house" means the living areas. Service areas such as bathrooms and laundries are not usually included. The air conditioning system is designed to condition the whole house at one time.

Due to the physical size of the air conditioner a circulation fan and heat exchanger unit is installed in the ceiling or under the floor with ducting to all rooms.

The compressor unit is located outside the building for ease of maintenance and to reduce indoor noise levels. Corridors act as a return air duct. The whole house can be conditioned to a comfort level controlled by a thermostat.

Zoned systems

The air conditioning is designed to efficiently air condition about half of the house at any one time, i.e. living areas or sleeping areas (excluding service areas as above), and is often referred to as a "night and day" system.

The simple operation of a change over damper directs the conditioned air from one part of the home to the other. Both installation and operating costs are cheaper than for the "whole house" system described above.

Air Conditioner Rating

Air conditioners are rated by the number of Watts of heat they can transfer. Some suppliers still quote the rating of the air conditioner in Btu/h (1,000 Watts = 3,412 Btu/h), and some quote the Horsepower (Hp.) of the compressor motor. Both of these are outdated units, and should no longer be used.

Air conditioners with an output capacity of less than 7,500 Watts (7.5kW), are required to have a prominent Energy Rating Label, which allows you to make a quick comparison of the energy efficiency of different units, and also make an estimate of running costs.
Air conditioners with low star ratings are less efficient (l star minimum) than air conditioners with high star ratings (6 stars maximum).

The labels also provide typical energy consumption figures in kWh for 500 hours of heating and cooling for reverse cycle air conditioners, and this can be used to estimate running costs.