Thermal Mass Research Project

At the University of Sydney Ben Slee is leading a research project into the use of thermal mass in lightweight (timber) houses in Australia. The project is funded by FWPA and supported by CSR.

This the project investigates how lightweight domestic construction can be made more thermally and energy efficient through a better understanding of the appropriate use of thermal mass.

"Thermal Mass" is a term used to describe materials that can absorb and store large amounts of thermal energy without significantly changing temperature themselves. Buildings that contain large amounts of exposed thermal mass (e.g. a stone church) have small fluctuations in internal temperature compared to light-weight buildings (e.g. a tent). The use of thermal mass to enhance thermal comfort is well documented in design guides and encouraged in legislation, although there is little or no information to help designers understand how much mass is required. The view that “thermal mass is good and therefore more thermal mass is better” is incorrect.

The use of thermal mass is not a solution to thermal comfort in itself. Mass must be used as part of a holistic design system that includes insulation, ventilation and a pattern of occupancy and other factors.

The project revealed some surprising results:

• You can have too much thermal mass.
• Too much thermal mass can reduce thermal comfort and increase annual energy use.
• Thermal Mass is more useful in some climates than it is in others. How, how much and where to use thermal mass depends on the local climate.
• The size and location of the windows has as large an influence on the thermal efficiency of a space as does the quantity of thermal mass.
• Thermal mass needs to be in one place to aid cooling and a different place to aid heating.
• The manufacture of high thermal mass materials often comes with a high environmental cost.
• The use of thermal mass may increase rather than reduce the whole life carbon emissions of a building.

 

A number of academic papers have been presented at conferences around the world as a result of this project. A guide to “Thermal mass in timber framed buildings” is being prepared in collaboration with Wood solutions.

Evaluating ‘Rules of Thumb’ for integrating thermal mass into lightweight construction in Australia – Slee and Hyde 2011
Can you have too much thermal mass? – Slee et al 2013