When conducting a 6 Star Energy Rating Assessment, our energy assessors take many factors into consideration beyond just the glazing and building envelope performance. It considers phenomenon such as building materials and their level of thermal mass.
The term thermal mass simply means the ability of a solid mass to absorb and store heat. Dense materials of a high mass require a lot of energy to heat up and can store the heat energy for longer, such materials are said to be a high thermal mass e.g. concrete, bricks, earth, tiles. Lightweight materials like wood do not take long to absorb heat but also cannot retain it for as long and are termed as low thermal mass.
What is important is not just a material’s ability to retain the heat but they also release it back to the environment steadily depending on their thermal mass. This is known as phase lag. This phenomenon is very useful for building thermal performance. At Energy Rating Perth, our energy assessors can decide depending on net target interior temperature required as it can be used to heat or cool a space. Let us take the example of a polished concrete floor, which has a high thermal mass. In winters, if the floor has enough solar access through glazing, it will slowly heat up during the day and at night it will re-radiate that heat back into the space. In summers, the same floor will act as a heat sink during the hot summer day removing the unwanted heat from the room, as it will be a cooler body. During the night, if the space is well ventilated, when the floor releases heat, the cross ventilation will remove the heat from the room causing a comfortable internal environment. You can consider these materials as a thermal battery, with dense materials being able to store more energy than their lightweight alternatives.
However thermal mass should not be considered a substitute for insulation as a thermal mass may store and re-radiate heat, but insulation will increase the thermal resistance of your building by inhibiting heat exchange. A material with a high thermal mass may not be a good thermal insulator.
When thermal mass is used correctly it moderates internal temperatures by averaging out the day and night extremes. By avoiding these extreme temperatures, it increases comfort and reduces the need for external devices, such as air-conditioning, in turn reducing energy costs. However, a thermal mass is only efficient when the difference between night and day temperatures is a minimum of 6°.
Poor use of thermal mass can make for a very uncomfortable living environment, it can exacerbate the worst extremes of the climate. During a hot summer’s night, you might find the walls radiate heat. On a cold winter’s night, it may absorb all the heat you produce. To manage Thermal Mass, it is important that you consider other passive environmental measures, such as Orientation, controlling what amount sunlight enters the house at what time of the year. If you feel the building is overheating or has a poor solar access, read our articles for the solutions to these.
Our Energy Assessors at Energy Rating Perth urge our clients to use thermal Mass as part of your passive energy efficiency design, not only will you find it easier to receive a positive energy rating but you’ll reduce your carbon footprint and in turn make savings on your home’s heating and cooling loads.