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The energy consumption or power input of an air conditioner is measured under conditions specified in an Australian Standard. Because air conditioner use is affected by climate and this varies substantially across Australia, the cooling and/or heating Power Input shown on the energy label is the energy the air conditioner uses per hour at rated capacity (the units on the label are in kW which is the same as kWh/hour). To work out the annual energy use will require information on the climate and other factors such as occupancy (hours that cooling is required) and building shell performance (insulation, glazing, orientation etc). It is important to note that under normal usage, the air conditioner will spend a significant amount of time at less than its rated capacity - in terms of efficiency this is really only important for variable speed drive models.
The measure of energy service for an air conditioner is the rated cooling and/or heating capacity of the air conditioner, usually specified in kilowatts (some product brochures use BTUs, although this is now unusual and some retailers use compressor "horsepower", although this has no meaning in terms of the units capability). These rated values are as declared by the manufacturer and the test conditions are defined in the Australian Standard. The heating capacity of a reverse cycle air conditioner is the heat that can be put into a room. Similarly, the cooling capacity is the heat that can be removed from a room. The cooling capacity is made up of the sensible component (usually the majority of the capacity) which relates to the actual temperature reduction (cooling) of the air, plus the latent component, which is a measure of the dehumidification effect of the indoor air. Latent cooling capacity is sometimes expressed as moisture removal capacity in litres or kg of water per hour (1 kg per hour of moisture removal is equal to 683 Watts latent capacity).
Refrigerative air conditioners (the only type covered by energy labelling in Australia - evaporative units are not included) use a technique called the vapour compression cycle to "move" energy in the form of heat from one space to another. This is generally a very efficient process and the amount of heat moved is typically 2 to 3 times (or more) the energy required to run the compressor system. This ratio is called the Energy Efficiency Ratio (cooling) or Coefficient of Performance (COP) and is used as the basis for determining the star rating of an air conditioner (see below). The efficiency of the system depends on the components used (their design and how well these are matched) and the temperature difference between inside and outside (as the temperature difference increases, the system becomes less efficient).
The system uses a refrigerant (which exists as a gas at low pressure and as a liquid under compression) which is compressed and liquified, allowed to cool in a condensor, and then allowed to expand to become a gas in an evaporator (the expansion is accompanied by a strong cooling effect). In this operation the condensor becomes warm and the evaporator becomes cold as the heat is moved from the evaporator to the condensor.
The principle is the same as used in a normal refrigerator which "moves" heat from the inside of refrigerator to the outside. In the case of an air conditioner, when in cooling mode the heat is removed from the room being cooled and pushed outside through the refrigeration system. Similarly, if the unit can operate in "reverse" (so called heating mode or reverse cycle), the process runs backwards and the energy is collected from outside and moved inside to the room being heated.
To be eligible for an energy label (and to comply with MEPS), an air conditioner must meet the maximum cooling test as defined in the Australian Standard - this ensures that the air conditioner is capable of operating under extreme conditions. The air conditioner also has to have a tested capacity of not less than 95% of the rated value and a tested energy consumption of not more than 105% of the rated value.
The star rating for air conditioners is determined differently to other appliances. 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. The Star Rating Index is calculated on the tested values for energy and capacity, rather than the nameplate or rated values.
Typically, the EER and COP are in the range 2.0 to 3.5 (meaning that the cooling or heating output is 2 to 3.5 times as great as the power input, or an efficiency of 200% to 350%). 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 they require as electrical power input.
The star rating for air conditioners is determined from the tested EER and COP. For cooling, 1 star is equal to an EER of 2.0 with an extra star for an increase in EER of 0.3. For heating, 1 star is equal to a COP of 2.3 with an extra star for an increase in COP of 0.3. (these are the revised star rating scales from 2000).
From October 2004, all single phase air conditioners will have to meet Minimum Energy Performance Standards (MEPS), which specify minimum levels of energy efficiency for these products. All three phase air conditioners have been required to meet MEPS since October 2001. You can find details of the current and future MEPS levels for air conditioners on the web page that decribed MEPS for air conditioners in detail.
The detailed star rating equations are contained in the document 
"Equations for Appliance Star Ratings".
There is an overview of how star ratings are calculated for other products on this site.
This page last modified 28 June 2007
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