How are refrigerator star ratings calculated?

Comparative energy consumption CEC

The energy consumption of a refrigerator is measured under conditions specified in an Australian Standard. Over a year, this value is known as the comparative energy consumption or CEC.

Concept of adjusted volume

The measure of energy service for a refrigerator is the volume that has to be cooled. However, freezers operate at a much colder temperature than fresh food compartments, so the volume of these compartments is "adjusted" to take account of the extra energy required to achieve this task. The energy service provided by a refrigerator or freezer is called the total adjusted volume (which is the "equivalent" fresh food volume of all compartments taking into account their temperature of operation).

Performance

To be eligible for an energy label a refrigerator has to meet a temperature operation test and a pull down test as defined in the Australian Standard. Refrigerators also have to meet the Minimum Energy Performance Standards (MEPS) requirements for minimum energy efficiency.

Base Energy Consumption BEC and Star Rating

The Base Energy Consumption defines the "1 star" line for particular products. An additional star is awarded when the CEC of the model is reduced by a defined percentage from the BEC. Energy reductions per star from 2010 are set at 23% per star. For example, a CEC that was 0.77 of the BEC or less would achieve 2 stars. Similarly, a CEC of 0.5929 (0.77 x 0.77) of the BEC or less would achieve 3 stars and so on. The PDF document below sets out the detailed equations for the calculation of star rating.

For refrigerators and freezers, there are a total of 10 groups which have been defined under the standard. However, to determine star ratings, a number of these groups are compared on the same basis, especially where they are performing a similar task, so from 2010 there are only 3 BEC rating scales which cover all 10 refrigerator and freezer groups.

Refrigerators and freezers are a special category of product under the energy labelling program as they are also subjected to Minimum Energy Performance Standards or MEPS. The effect of the MEPS requirements for refrigerators and freezers was considered when the BEC lines were developed. The new BEC lines for 2010 are based on curves which have been developed on the basis of estimated surface (adjusted volume to the power of two thirds) area rather than adjusted volume which has been used previously - this helps reduced the effect of size bias.

The original star rating equations for refrigerators were developed in 1986. 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 (for example, new refrigerators today use 70% less energy than equivalent products from the 1980's). 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.

Refrigerator energy label

What about adaptive defrost?

Adaptive defrost is smart technology for frost free refrigerators and freezers where the appliance adjusts the frequency of automatic defrosts to match frost load on the evaporator. Adaptive defrost systems are recognised by the Australian Standard for refrigerators and freezers but at this stage a test to assess the performance of these controls under a range of conditions is not yet included in the test method. However, regular checks are undertaken during check testing to ensure that such controls are not circumventing the requirements of the standard. The standard assumes that at least one defrost per day will occur during normal operation, although some smart systems may have a longer time between defrosts under normal conditions of use. An adaptive defrost allowance of 1.05 is included in the MEPS levels but this allowance is not included in star rating equations.

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 09 September 2010