To allow fair comparisons between homes, NatHERS software models heat loads based on conditions under which occupants are most likely to be thermally comfortable within their home.
These conditions vary according to many factors including:
- the likely acclimatisation of the occupants to the local climate
- the impact of the local climate on each space in the home (using the Reference Meteorological Year weather file for the climate zone)
- the primary function or functions of each space in the home
- the time of day a space is expected to be used
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Occupancy hours
To allow homes to be compared fairly a standard occupancy pattern is applied that represents a reasonable expectation of how each space in that home is used, based on its function.
For the purpose of assessing a building under NatHERS, the software allocates functions to each space in a home, along with a period of time during which the space is likely to be used and required to be kept at a comfortable thermal range. For example:
- For living spaces: thermal comfort is maintained from 7.00am to midnight
- For sleeping spaces: thermal comfort is maintained from 4.00pm to 9.00am
Thermal comfort
NatHERS software adjusts modelled temperatures to achieve thermal comfort through three means:
- by natural means (e.g. open windows)
- cooling via mechanical air movement (e.g. ceiling fans)
- by adding or extracting an amount of energy to that space via heating and cooling appliances and equipment
All external openings (e.g. windows) are considered to be operable at all hours, although a factor has been incorporated to limit the number of operations to one per each three hour period.
Heating thermostat settings
The heating thermostat setting varies according to the function of the space and the expected clothing level in that space during a particular time period. For example, a lower minimum heating thermostat setting is used during sleeping hours to reflect the likelihood of bedding (sheets, blankets, quilts etc.) being used.
- For sleeping spaces (including bedrooms and other spaces closely associated with bedrooms): a minimum heating thermostat setting of 18 degrees Celsius is used from 7.00am to 9.00am and from 4.00pm to midnight; and a heating setting of 15 degrees Celsius from midnight to 7.00am.
- For living spaces (including kitchens and other spaces typically used during waking hours): a minimum heating thermostat setting of 20 degrees Celsius is applied.
Cooling thermostat settings
The cooling methodology is based on the Effective Temperature method of calculating thermal comfort. The cooling thermostat setting varies according to the climate zone to account for the acclimatisation of local residents. It also varies from room-to-room from the summer neutral cooling temperature of that climate zone to take into account the effect of air movement, air temperature and humidity level in that space on the occupants' perception of thermal comfort.
Further details about the specific thermostat settings for each NatHERS Climate Zone can be found in the NatHERS Software Accreditation Protocol