Eastern Energy Raters

NatHERS

The Nationwide House Energy Rating Scheme

The Nationwide House Energy Rating Scheme (NatHERS star rating) is a star rating system, out of ten,  that rates the energy efficiency of a home, based on its design.

By providing a ‘measuring tape’ to estimate a home’s potential heating and cooling energy use, NatHERS helps to make Australian homes more comfortable for their inhabitants and also helps residents to save on energy bills through smarter design choices. Often good design can reduce the amount of energy needed to keep a home comfortable with no or little additional construction cost

The Nationwide House Energy Rating Scheme

When calculating a NatHERS star rating, NatHERS Accredited Software models expected indoor temperatures based on data specific to that dwelling. This includes information on design and construction, climate and common patterns of household use. The software tools do not take into account electrical appliances in the dwelling, apart from the air flow impacts from ceiling fans.

Using the software user interface, a NatHERS Accredited Assessor enters data to develop a simulation model of the house or apartment, including:

  • size and function of rooms
  • size and specification of openings
  • building materials/windows/products
  • type of construction
  • dwelling orientation
  • location

The software will then model how much cooling or heating occupants may need to stay comfortable during a typical year. It does this by firstly simulating how the local climate heats and cools the house every hour of every day of the year.

Once internal temperatures fall outside a comfortable range, the software models the need for heating and cooling on the assumption that the occupants of the house will firstly open and close windows and any blinds or awnings to restore comfortable internal temperatures (when it makes sense to do so) before using any heating or cooling system. The total estimated annual heating and cooling requirements are then converted to a star rating out of 10 stars.

To enable comparison across different homes each software package uses the same:

  • climate zones
  • weather files
  • occupancy settings for a ‘standard family’
  • internal heat loads
  • star rating scale for the home’s location

NatHERS Climate Zones and Weather Files

NatHERS divides Australia into 69 climate zones. This allows the software to appropriately consider the effects of Australia’s diverse climate when modelling the heating and cooling requirements of a home.

Weather files have been compiled from Bureau of Meteorology records for each NatHERS climate zone and include information on air temperature, humidity, solar radiation and wind speed and direction. The weather file for each climate zone, called the Reference Meteorological Year (RMY), is compiled from at least 25 years of Bureau records.

When conducting a NatHERS star rating, the software uses the weather files to assess the impact of weather on the building’s internal temperature. This impact is calculated for every hour in a full 12-month period.

Above information obtained from Nathers

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