Frequently Asked Questions – Air Conditioners

What types of air conditioners are NOT required to carry an energy rating label? The following air conditioners are not currently required to carry an energy rating label: evaporative air conditioners, three phase air conditioners (these may carry a label on a voluntary basis but are unusual for the residential sector), multi-split air conditioners (units with several separate indoor units each with a separate control), air conditioners intended purely for commercial applications and portable air conditioners. See Requirements for air conditioners for a more detailed list of exemptions.
How can the capacity output of an air conditioner be greater than the power input? For air conditioners, the measure of energy efficiency is the Energy Efficiency Ratio (EER) for cooling and the Coefficient of Performance (COP) for heating. The EER and COP are defined as the capacity output divided by the power input. This is achieved by the use of a refrigeration heat pump which collects internal heat and moves it outside when in cooling mode, or collects ambient heat from outside and moves it inside when in heating mode. The apparent efficiency of heat pumps is high as they can move much more low grade energy in the form of heat than the electrical energy they require. You can find out more information in How are air conditioner star ratings calculated?
What size/type of air conditioner should I purchase for my home? Before purchasing an air conditioner you should consider other non-energy consuming means of providing a comfortable home environment during the warmer months of the year. The design of your house can significantly affect the internal comfort conditions. Features that can significantly reduce or eliminate the need for refrigerative air conditioning include:

  •  House orientation for exposure to cooling breezes.
  • Increase natural ventilation by reducing barriers to air paths through your home.
  • Provision of fans to provide ventilation and air movement in the absence of breezes.
  • Floor plan zoning to maximise comfort for daytime activities and sleeping comfort.
  • Appropriate windows and glazing to minimise unwanted heat gains and maximise ventilation.
  • Effective shading (including vegetative planting).
  • Adequate levels of appropriate insulation.
  • High thermal mass construction in regions with significant diurnal ranges (i.e. large variation between daily minimum and maximum temperatures).
  • Low thermal mass construction in regions with low diurnal range (i.e. small variation between daily minimum and maximum temperatures).
  • Use of light coloured roofs and walls to reflect more solar radiation and reduce heat gain.

Such features can be built into your new home or retrofitted into an existing dwelling. For further information on these energy saving options go to the Your Home web site. If in your circumstances you decide that an air conditioner is warranted then it is important that you not only purchase an energy efficient one, but that it is properly sized and correctly installed. This is a job for appropriately qualified designers and installers. Information on this subject can be found at the Australian Institute of Refrigeration, Air conditioning and Heating (AIRAH) web site.

Sizing an air conditioner is best undertaken by a professional. But you can save significant amounts of capital expense if the air conditioner is sized correctly to take account of your building shell. If you live near a coastal area and have a very efficient home, you may be able to get by without an air conditioner. However, there is more information at the Living Greener site.

Why does the star rating of some air conditioners sometimes seem inconsistent with the capacity output and the power input? The star rating and star rating index for an air conditioner is not based on the rated power input and the rated capacity (as published on the web site) but rather it is based upon the tested power input and the tested capacity (not published on the web site) when tested in accordance with AS/NZS 3823. For energy rating labelling, tests are conducted on a unit and the tested power input and tested capacity is used to determine the star rating index.The rated values are those marked on the name plate affixed to the air conditioner in the factory during production (usually overseas). AS/NZS 3823 requires that for an energy rating test to be valid the tested power input must be no more than 5% higher than the rated value and the tested capacity must be no more than 5% less than the rated value. This tolerance means that there is not always an exact relationship between the rated power input, the rated capacity and the star rating index – although it will be relatively close.You can find out more details on the page: How are air conditioner star ratings calculated?
What is an ’inverter‘ air conditioner? An inverter model means that the compressor is powered by a variable speed drive or ’inverter‘, which enables the compressor to run at a range of speeds from slow to fast, to match the output required. Most conventional compressors run at a constant speed and these types of units vary their capacity by switching on and off at different intervals. Inverters are a sophisticated piece of technology which improve the performance and energy efficiency of air conditioners under normal use. Inverter models are marked in the web site listing for air conditioners. See also next question.
Why don’t ‘inverter’ type air conditioners get a higher star rating? For standard air conditioners (which use single speed compressors) the efficiency does not vary significantly at part load – reduced load output (heating or cooling) is achieved by the unit turning on and off through the thermostat or temperature control system. Inverter units use a variable speed drive in the motor system that drives the compressor. While these systems tend to look less efficient at full load (i.e. their star rating at rated capacity, which is the rating on the energy rating label, is not always as high as conventional air conditioners), they tend to be very efficient at part load operation, which is a more common mode in a typical household. This is achieved by reducing the continuous compressor output which increases the efficiency of the refrigeration system (as the apparent size of the condenser and evaporator is larger). Performance does vary between models, so the actual part load performance of inverter units should be sought from manufacturers. Inverter units are now marked on the air conditioner energy rating product listing and part load efficiency data is also available for some inverter models.
Are evaporative coolers more energy efficient than conventional air conditioners? As a rule, evaporative air conditioners will use less energy than an equivalent ‘vapour compression’, or refrigerative type of air conditioner. However, a fair comparison of these products is always fraught with difficulty. Evaporative air conditioners rely on the evaporation of water to cool the air (‘evaporation is accompanied by a cooling effect’) and so increase the humidity in the cooled space. These types of systems are really only effective in dryer climates. Unlike conventional air conditioners (which remove moisture from the cooled space and work best in a sealed room), evaporative air conditioners require a large volume of fresh air to pass through the house, so ventilation to allow internal air to escape is essential. Evaporative air conditioners can also consume substantial volumes of water, which may be an issue to consider for homeowners.
How is the total cooling capacity of an air conditioner determined? A conventional ‘vapour compression’ air conditioner has two main components which make up the cooling capacity. The first is the so called sensible cooling effect – this is the energy equivalent of the temperature change of the air that flows across the air conditioner (temperature fall multiplied by mass flow rate of air). The sensible cooling capacity is by far the largest component of capacity for most air conditioners and is expressed in Watts (W) or kilowatts (kW). The second component is called the latent cooling effect or dehumidification effect and is determined by the amount of moisture removed from the conditioned space. Sometimes this is expressed as litres of moisture removed per hour, but is usually expressed as Watts or kW when added to the total capacity. One kg of moisture removed per hour equates to a latent cooling capacity of 683 Watts.
What does the term ‘horsepower’ mean in terms of an air conditioner capacity? The ongoing use of ‘horsepower’ by retailers is of concern to energy regulators in Australia. This term bears no relation to the output capacity of the unit. The only valid capacity measure is the kW output under AS/NZS3823 condition T1 for cooling or H1 for heating. The term ‘horsepower’ came from a time when air conditioner compressors where driven with mechanical motors. The output of an air conditioner depends on the motor efficiency, the compressor efficiency, the evaporator and condenser design and heat transfer properties, relative size of the evaporator and condenser, air flow design over the evaporator and condenser, fan efficiency and size, control system etc. Defining the input or output power of the electric motor in such a system as a proxy for capacity is completely misleading in all cases.
Are there any regulations that limit starting currents or which mandate the installation of ’Soft Start Devices‘ for air conditioning units in Australia and New Zealand? Yes. Some electrical network operators in Australia do set limits on the maximum start current that an air conditioner can demand – to meet these limits, soft starters are usually required (i.e. to limit in-rush current to acceptable limits). An overview of the respective State, Territory and New Zealand requirements are set out in the summary of service and installation requirements – this page has links to information on soft start/maximum current requirements. Australian regulations for energy efficiency do not directly prescribe soft start technology for air-conditioning equipment.