Rule 4: Don’t heat with one hand and cool with another
A large part of creating an energy efficient house is knowing how, when and where to keep the outside conditions on the outside.
And that’s not chicken-feed stuff: In Australia we spend about 44.7% of our residential energy usage – about 170 PetaJoules per year (170,000,000,000,000kJ, or about 5.9 million tonnes of coal equivalent )- on heating and cooling our homes. (That figure’s about 5.1 quadrillion Btu in the USA, equivalent to about 5401PJ or 186 million tonnes of coal).
That’s a mighty load of go-juice spent making the inside of our houses more comfy than the outside. And, depressingly, an awful lot of this energy goes to waste.
From my experience, there are three main ways our homes waste this heating-and-cooling energy:
The first path to waste in our homes – and by far the biggest, in the temperate-climate Australian context – comes from building houses that leak heat, inwards or outwards. There are two ways to fix this: To seal the gaps in our houses, where warm air can enter or escape, and to insulate, insulate, insulate.
The second is by failing to use what we get for free. Failing to admit winter sunlight, or failing to store daytime heat for night-time use (through thermal mass or other energy-storage systems). Failing to cool our houses through night-time breezes or convective cooling. Failing to use evaporation, or to plant trees in the right places.
The third – and in some ways the most insidious- is by heating with one hand and cooling with another.
You can see an example of this every time an air conditioner runs with uninterrupted summer sunlight beaming into a room, or trying to cool when inefficient heat-emitting appliances are running. (In our office our laser printer alone puts out enough heat to raise the temperature two or three degrees. Nice in winter, but not so much fun in summer).
I’ve heard it said that a problem well defined begins to solve itself, and that principle can be applied to energy efficient house design. Look at your site, your situation and your energy sources. Know where your heat is going to come from, your sunpath and wind directions, and you’ll begin to know how to shield from it. Likewise, knowing your potential paths of heat loss; your gaps and uninsulated areas, will show you how to block and insulate them.
The trick is to address your energy gains or losses at the source, rather than developing active systems to counter them.
It’s simple stuff, but even professionals get it wrong sometimes. It involves a change of mindset – a new thrift, rather than just throwing more energy at a problem.
I once worked on a multi-purpose hall for a primary school where a mechanical engineer proposed an air conditioning system that over-cools the air, then precisely adjusts the temperature by re-heating it again. As he explained the drawings, I sat, dumbfounded. Worse, he was astonished at my astonishment.
This type of inefficient thinking is everywhere, and it’s madness.