Refrigerative air conditioners remove heat from the air inside the home and transfer it outside. They cool, dehumidify and recirculate room air. Unlike evaporative cooling systems, as long as they are sized correctly, they work effectively in any climate. However, they are the most expensive form of cooling to purchase and operate.
Types of air conditioners
Air conditioners can be:
- window/wall units, which are designed to cool a single room or open plan area
- split systems in a single room or with multiple outlets – these have a separate indoor air handling unit and an outdoor compressor unit connected by refrigeration piping, keeping most of the noise outside
- ducted systems, which cool the whole house through multiple ceiling outlets – these have a central air handling unit that is usually located in the ceiling space and a single compressor located outside connected to the air handling unit by refrigerant piping.
Inverter air conditioners have a variable speed (or inverter-driven) motor. Rather than switching the compressor on and off, they automatically vary the speed of the compressor, running it at full speed when cooling demand is high and a much slower speed when cooling demand is low.
Inverter air conditioners are quieter to run and give additional energy savings compared to the standard air conditioners.
Most split system air conditioners these days are inverters.
Sizing an air conditioner
Having the right-sized air conditioner is vital for efficient operation and to achieve the desired comfort level. .
If your system is too big for the space it is cooling, it will have short cooling cycles (switching on and off) resulting in increased power consumption and excess wear and tear on your unit. This is likely to be a greater concern with standard air conditioners than with inverter models.
If your system is too small, it won’t provide adequate cooling. This will result in the unit working harder than it is designed for, increasing maintenance requirements and potentially shortening the life of the unit.
The best way to ensure that you have the right-sized unit is to have a full heat load calculation carried out by an authorised air conditioner installer or manufacturer before you purchase. This is best done in your home so that factors such as ceiling heights, window sizes and orientations, and insulation levels can be taken into account.
Once you’ve established what size you need, use the star ratings on the energy rating labels to compare the energy efficiency of air conditioners.
When you obtain a quote for an air conditioner, it is important that the cooling and heating (if reverse cycle) output of the unit is quoted in kilowatts (kW), so that you can compare different models.
It will also be useful to obtain the rated input power consumption (in kW) of the unit on both its cooling and heating cycle if the system is a reverse cycle unit.
Energy rating labels
Cooling-only and reverse cycle models must display energy rating labels. The labels carry a star rating from 1 to 6 stars – the more stars the more efficient the unit and the lower its running costs will be.
Cooling efficiency is indicated by the stars located in the blue band, and heating efficiency is indicated by the stars located in the red band. Super-efficient models could have a rating of 7 to 10 stars, with the extra stars located in a crown at the top of the label.
Tips for operating refrigerative air conditioners
Follow these common sense tips when using an air conditioner:
- keep window and doors closed when the system is operating to avoid wasting energy
- thermostats should be set between 24 and 26°C – every degree lower in summer will increase running costs by around 10%
- turn your system on only when it is needed, and don’t leave it running when you are out during the day as this wastes energy and your money – it’s a myth that running your air conditioner 24/7 throughout summer means that it runs more efficiently
- avoid running your air conditioner all night unless you need to for medical reasons – a fan can generally keep you comfortable during the night at a much lower running cost
- turn the air conditioner off when the outside temperature drops, and open doors and windows to let the cool air in
- use the economy setting if your system has one – this setting reduces energy use by maintaining moderate rather than cold temperatures in appropriate conditions
- keep the area you are cooling to a minimum by closing doors to other rooms not requiring cooling
- use portable or ceiling fans wherever possible – they are much cheaper to run than air conditioners and can also be used in conjunction with your air conditioner
- use the zoning options of a central cooling system if they are available to reduce the area of your house you are cooling at any one time
- if your air conditioners compressor unit (the part located outside) is exposed to full sun during the day, shade it with an awning, shade mesh, or a similar structure – be careful not to restrict air movement around the unit
- Refrigerative air conditioners and evaporative coolers should be regularly serviced and maintained in accordance with manufacturer’s instructions to keep them operating effectively
- filters should be cleaned regularly and replaced in accordance with manufacturer’s instructions
- Ensure any ducting is free of air leaks— escaping cool air will cool your roof space instead of the inside of your home.