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The energy consumption or power input of an air conditioner is measured under conditions specified in an Australian Standard. Because the heating and cooling requirement is affected by climate and this varies substantially across Australia, air conditioner use is not shown on the energy label. Instead, the cooling and/or heating Output and the Power Input is shown on the energy label at rated capacity (the units on the label are in kW which is the same as kWh/hour). To work out the likely 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 output models which can have higher efficiency under part load conditions.
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 (kW) (some product brochures use BTUs (British Thermal Units), 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 under the test conditions are defined in the Australian Standard (which is based on the relevant international 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 low grade heat that can be moved is typically 3 to 5 times (or more) the energy required to run the compressor system. This ratio is called the Energy Efficiency Ratio (EER), used for cooling, or Coefficient of Performance (COP), for heating, and is used as the basis for determining the star rating of an air conditioner (see below). A refrigeration heat pump 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 efficiency of the system depends on the components used (their design and how well these are matched – compressor, evaporator and condenser) 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 liquefied, allowed to cool in a condenser, and then allowed to expand in a controlled way (through an expansion valve) to become a gas in an evaporator (the expansion is accompanied by a strong cooling effect). In this operation the condenser becomes warm and the evaporator becomes cold as the heat is moved from the evaporator to the condenser.
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" (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. In most cases, air conditioners are more efficient when operating in heating mode as the energy used to compress the refrigerant can also contribute to the net heating output.
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 measured values for energy and capacity during a rating test, rather than the nameplate or rated values.
The original star rating equations for air conditioners were developed in 1987. These were revised (re-graded) in 2000 and again in 2010 to take account of the substantial improvement in the energy efficiency of products over this period. Until 2010, all energy labels showed possible star ratings from a minimum of 1 star to a maximum of 6 stars. In 2010, the star rating system for refrigerators and air conditioners was expanded to show up to 10 stars for products that have exceptional energy efficiency. Products that achieve up to 6 stars continue to use a normal 6 star energy label.
The star rating for air conditioners is determined from the measured EER and COP. From 2010, for cooling, 1 star is equal to an EER of 2.75 with an extra star for an increase in EER of 0.5. For heating, 1 star is also equal to a COP of 2.75 with an extra star for an increase in COP of 0.5 Importantly, the 2010 star rating system is based on an annual efficiency calculation which includes any non-operational energy consumption such as standby and power consumption of crank case heaters (where present).
Since October 2004, all single phase air conditioners have been required 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. Revised MEPS levels were introduced in April 2010 and these will again be upgraded in April 2011. You can find details of the current and future MEPS levels for air conditioners on the web page that describes MEPS for air conditioners in detail.
Proposals for increased future MEPS are under consideration. Details are included in regulatory impact statements.
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 21 January 2011
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