Over the last decade or so, as the focus of commercial and residential architecture has shifted to ‘going green’, the popularity of thermal mass in construction has boomed. However the concept of thermal mass is nothing new. Ancient civilisations, particularly in desert climates, quickly realised and embraced the benefits of thermal mass. But first, what is it?
To break it down very simply, thermal mass is any material or element with the ability to store heat. Pretty much any item that you can think of has some potential as thermal mass. From a warm beach towel that’s been laid out under a summer sun, to an impossibly hot car steering wheel- basically things that heat up and stay hot!
The thing is, no one builds a house out of metallic belt buckles or beach towels- timber, steel, concrete, glass and bricks are far more popular. Using an example more closely related to common construction, have you ever spent a summer evening outside, perhaps having a barbeque on a paved (brick, tiled or concrete) area? Did you happen to notice that when the sun went down and outside air temperature dropped, that the bricks beneath your feet were still very warm? That’s thermal mass at work.
So we’ve established thermal mass is a material’s ability to store heat- so what? Well if we take the concept of thermal mass and harness this into our construction methods we will see huge energy and financial benefits. Without knowing the science behind what they were doing (and there are lots of formulas we could bombard you with here), ancient desert civilisations built their walls thick with mud, dung and stone. Despite these being some of the only building materials available to these civilisations, what they quickly realised was, the thicker they built these walls, the cooler they felt inside their shelters. On the flip side of this scenario, if Bear Grylls finds himself in Antarctica, would he build his igloo with 5cm thick walls of packed ice? No, he would make these walls as dense as he possibly could! Wall density, people- it’ll save your life
If Michael Limb Builders were contracted to design and build a house in Kakadu, we would make our walls of extremely thick stone or rammed earth; our floor slab too. As the harsh sun pounds the thick walls all day, due to their density, the heat of the sun will take much of the day to completely warm the depth of the entire thick exterior walls- keeping the internal temperatures free from this heat and cool. Essentially the greater the density (thickness) of a building material, the higher it’s heat capacity per unit of volume will be when compared to less dense (thinner) material. In the hot climate of Australia, this is paramount.
Due to its thermal mass properties, our now heated stone or rammed earth walls have the ability to store the heat they’ve been absorbing. Depending on the thickness of the walls, by the time they’ve heated up, it will be approaching the end of the daytime (or even the early evening). As our thick, say rammed earth walls, have a high capacity to store heat, i.e. a high thermal mass, they will stay warm for many hours after the sun has gone down, radiating heat to the interior during the cooler night time hours. This is important in desert climates as in many places in the world, Kakadu included, temperatures can drop to freezing; whereas the Michael Limb Builders built home stays warm when it’s cold outside, and cool when it’s hot outside. That is the basic principles of designing a home to combat extreme temperature changes in a diurnally shifting climate.
The same principles will work with a thick concrete slab in a residential building. As large north-facing windows heat the cool slab slowly during the day (again due to its density), that slab, which is now warm, will remain warm for most of the night due to its thermal mass properties.
Designing a home that considers both material density and thermal mass has the potential to save you, the homeowner, hundreds of dollars in heating and cooling bills annually. In fact, if your architect manages to do his job superbly, you may not ever need to mechanically heat or cool your home. This would be a 10-Star home. This will be the future of building- sustainable, smart and importantly, cheap! And will feature in one of our future blog posts.
For more information also visit http://www.yourhome.gov.au/passive-design/thermal-mass or read http://www.sanctuarymagazine.org.au/ideas-advice/design-matters/retrofitting-thermal-mass-into-walls-and-floors