How does EER software work?

An EER, or Nationwide House Energy Rating Scheme star rating, depends on how much cooling or heating a ‘standard family’ (the occupants) may need to stay comfortable during a typical year. NatHERS accredited computer software simulates how heat enters and escapes a house every hour of every day of the year, assuming the occupants open and close windows and any blinds or awnings to make best use of the local climate.

There are 3 different accredited, second generation software packages, each uses the same:

  • weather file

  • occupancy settings for a ‘standard family’

  • heat loads

  • star rating scale for the home’s location.

(NB. the EER tool used in the ACT for existing houses at time of sale is old, first generation software, that has not been used for new designs, anywhere in Australia, since 2009. It is much more simplistic, and much less informative, than second generation software)

At Light House we use BERS Professional Version 4.2.110811. We use the software to assess and optimise the thermal performance of our designs from the very beginning of, and throughout, the design process. The software is a powerful tool that should be used for much more than ticking a box at the building approval stage – sadly this is when most house designs are first assessed for their energy efficiency. If EER is considered early, it is quite simple to achieve 7+ star designs in our climate, often without any extra expense.


Weather files

Weather files are compiled from Bureau of Meteorology records and include air temperature, humidity, solar radiation and wind speed and direction. For the purpose of rating a house within a single climate zone, the impact of the weather on the building design is calculated every hour for a full 12 month period.

This 12 month weather file for each climate zone, called the Reference Meteorological Year (RMY), is compiled from no less than 25 years of Bureau records,

Read more about weather files and climate zones.

Occupancy settings

These are rules incorporated into the software for what type of rooms the occupants are using at different times of day and the temperatures that cause them to cool or heat the rooms. The temperatures vary from climate to climate because studies show that people adapt to their local conditions.

Read more about occupancy settings.

Heat loads

The software takes into account the internal ‘heat load’ of a building that impacts on its thermal comfort. This includes humidity, occupant-generated heat and heat generated from appliances and equipment.

Read more about heat loads.

Star rating scale

The software calculates the family’s annual combined cooling and heating needs, which are compared to the size of the home (with an area correction factor applied to allow fair comparison of different sized buildings in different locations) and the NatHERS scale to set the star rating.

Achieving a minimum of six stars is easy. To see how you can design or modify your desired design to achieve a result above the minimum requirement, visit the Your Home website.

Read more about area correction factors and the star rating scale.