The thermal capacity of concrete and concrete masonry, often referred to as its thermal mass, enables it to absorb, store and later radiate heat. Exposed concrete can absorb heat during the daytime, reducing temperatures by 3° to 4°C, and delaying peaks in temperature by up to six hours.* During the night, natural ventilation is used to cool the concrete, priming it for the next day.
Some 90% of the total energy used in buildings is for heating, cooling and lighting. Employing the thermal mass of concrete can reduce or even eradicate energy-intensive air-conditioning, while maintaining a comfortable temperature for occupants. To optimise concrete’s thermal mass, it must be used in conjunction with higher thermal insulation, window placement for good solar gains and natural ventilation as part of an integrated and sustainable passive design.
There has been extensive research modelling the performance of thermal mass in residential housing under New Zealand environmental conditions.** Thermal mass can also be effectively used in the commercial sector, with the Maths and Computer Science Building at Canterbury University an excellent example.
The use of concrete and concrete masonry in homes enables reduced energy consumption for heating through improved air-tightness. Further financial savings can be achieved as a result of concrete’s ability to reflect natural light and therefore reduce the need for artificial lighting.
*Designing comfortable homes: guidelines on the use of glass, mass and insulation for energy efficiency. (2001). Wellington, New Zealand. Cement and Concrete Association of New Zealand.
**Gjerde, M. & Munn, C. (2003). A comparison of cost and thermal performance of concrete and lightweight housing systems In New Zealand, Proceedings of the 21st Biennial Conference of the Concrete Institute of Australia. Brisbane, Australia. 2003.