One of those frequently occurring eco-building terms, thermal mass is often mentioned but rarely defined.
The thermal mass of a building is an assessment of the ability of its internal fabric to absorb and store thermal energy. Through absorption of heat, the temperature of a material increases – the amount of heat that must be absorbed to raise the temperature of a material by one degree varies by material. This ability to absorb heat is measured by the Specific Heat Capacity of the material (SHC). The SHC is a measure of the amount of heat energy required to raise 1KG of the material by 1 degree Celsius. Those materials that require most heat to increase in temperature have a high thermal capacity (also know as high volumetric heat capacity), such materials are typically dense in composition and ideal for storing thermal energy – these are materials such as brick, concrete and stone.
As a major element of our heating and cooling strategy, through passive solar design, we will seek to employ thermal mass in harnessing the energy of the sun during the day and releasing it during the night when it is needed.
In the Summer, the thermal mass will provide a buffer to over-heating, absorbing thermal energy and reducing the peak temperature whilst moving the time of the peak later into the evening.
In the Winter, high thermal mass buildings will take longer to initially heat up, but with regular occupation will retain the heat for longer and will reradiate heat comfortably overnight when it is required.