- Owners and Builders
Thermal mass is a material’s ability to heat or retain heat over time and is based on the conductivity, density and specific properties of the material. High thermal mass, like a masonry box, means it is less impacted by changes in external temperature compared to a lightweight timber box.
The thermal mass formulas used by the NatHERS calculation engine (Chenath) were developed from 1953 work by former CSIRO scientist Dr R.W Muncey’s. As you can see in the results below, Muncey’s experiments showed a construction having high thermal mass was less impacted by changing external temperature, both in actual observations and predicted modelling.
Thermal mass is a fundamental element considered in NatHERS software tools. The software calculates how much heat is transferred and potentially generated in a dwelling by considering its orientation and construction (the construction material properties that include thermal mass) combined with occupancy settings, and hourly climate data of its location. This information simulates an internal temperature. If that temperature falls or exceeds the thermostat setting for heating and or cooling, the software triggers a calculation of predicted energy use that would be required to maintain the internal temperature within the thermostat limits.
View the full paper by Dr R.W Muncey’s work here: The Calculation of Temperatures Inside Buildings Having Variable External Conditions