Eco Living
The Beauty of Thermal Mass, Temperature Control Without the Dial
What exactly does 'thermal mass' mean, and how can we get it into our homes?
It’s been around since Roman times, so it’s not exactly new, but we currently hear the term ‘thermal mass’ bandied around when we talk about passive solar design and sustainable homes. So what exactly does it mean? If you want to maintain a comfortable temperature all year round in your home with minimal use of heating or air-con, read on for a clear break down.
Materials matter. ‘Thermal mass’ describes a material that has the ability to absorb and store heat. Materials with high thermal mass take a long time to heat up and to cool down. So in cool weather, thermal mass can absorb heat, store it and slowly emit it at night, while in warm weather, thermal mass can help to maintain a building’s cool when used correctly. Brick, for example, has thermal mass, but timber floors and brick veneer do not.
Other examples of thermal mass materials are concrete, rammed earth, stone and ceramic tiles.
According to Ngaio Fitzpatrick of building design company Strine Environments in Canberra, designing with thermal mass can help to maintain a comfortable temperature of around 20-25 degrees all year round, even in climates with such extremes as Canberra, where it can be 40 degrees in summer and reach minus six degrees in winter.
Strine Environments like to use concrete slabs and precast concrete walls to bring thermal mass to the homes they design and build. For anyone that doesn’t like the look of lots of concrete, here it is perfectly balanced by the use of timber – a material that many people find visually warmer than concrete.
Horizontal and vertical. While we often think of floors such as concrete when we think of thermal mass, it can also be used vertically, such as internal walls made of brickwork.
Here a CMU (concrete masonry unit) wall provides thermal mass to the home. The extensive glazing and skylight allow sunlight onto the wall to warm up the thermal mass.
While in this home a rammed earth wall acts as both a screen and a source of thermal mass.
In this home, the wall on the left is formed from a concrete block but has been plastered. The wall of glass on the right is shaded in summer but in winter allows the warmth of the sun to hit the concrete wall and tiled floor.
Liquid mass. Water can even be used as thermal mass. In this home, a line of fibreglass water tubes are filled with water and clad with copper at the top to allow for maintenance. At night, LED lighting illuminates the tube for a special effect. It’s an interesting concept though many would probably prefer to opt for a rammed earth, brick or precast concrete!
Day and night. Thermal mass is particularly good for climates with a high ‘diurnal’ difference, which simply means a big range between day and night temperatures. This is the case for many climates in Australia, including dry desert climates, but less so for tropical climates (though designed effectively, thermal mass can still be used for tropical climates). Use of thermal mass will help to regulate these environments and keep the temperatures constant.
Good glazing. Thermal mass needs to be used in conjunction with other passive solar design techniques, such as orientation, glazing, and insulation.
Large areas of glazing on the north side of the home allow the sun to hit the thermal mass so that it can absorb heat. The amount of glazing and where it’s located depends on the regional climate.
Large areas of glazing on the north side of the home allow the sun to hit the thermal mass so that it can absorb heat. The amount of glazing and where it’s located depends on the regional climate.
In summer the thermal mass should be protected from the sun by the angle of the eaves or from shading. This allows the slab to draw cool from the earth and help to maintain lower temperatures even on hot days.
Let the sun shine on. Materials such as wool rugs and carpet, though we like them for their warmth underfoot, are not thermal mass, so use them strategically and ensure some sun is hitting the slab floor directly in winter for it to be effective.
Upfront investment. Given the ability of thermal mass to control temperature, you would think we would all be using it. But, as with many investments, the initial outlay can be expensive. As Ngaio says, pre-cast concrete walls are more expensive than gyprock. Weigh up the long term benefits, though, because future savings are likely to outweigh the upfront investment.
Sustainability. The same goes for the ‘sustainability’ principle of thermal mass – there can be high ‘embodied energy’ in building with thermal mass, such as concrete, in that a great deal of energy goes into its manufacture. But this can often be balanced against the potential future energy savings.
Existing homes. While we don’t all have the luxury of building from scratch and adding thermal mass into our homes at the start, there are ways to bring thermal mass into existing homes or renovations. Uncover an existing concrete slab, for example. The old carpet could be removed and the slab polished or tiled with appropriate ceramic tiles. Brick walls could be added for vertical thermal mass. Consult an architect or building designer who specialises in sustainable design for the best ways to add effective thermal mass to your home.
Ancient ideas. Even though it may sound technical, using thermal mass is not a new idea. “It sounds complex, but it’s actually simple and is using principles from Roman times,” says Ngaio. “They used thermal mass to keep their buildings cool; they didn’t have air-conditioning.”
TELL US
Have you used thermal mass in your home? Please tell us about it in the Comments section.
MORE
Concrete is Cool, But Warmer Than You Think
8 Surprising Ways to Use Concrete That Won’t Leave You Feeling Cold
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9 Principles of Effective Passive Solar Design in and Around the Home
TELL US
Have you used thermal mass in your home? Please tell us about it in the Comments section.
MORE
Concrete is Cool, But Warmer Than You Think
8 Surprising Ways to Use Concrete That Won’t Leave You Feeling Cold
10 Ways Passive Solar Design Can Slash Your Energy Bills
9 Principles of Effective Passive Solar Design in and Around the Home