Diagram Architects

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.

Sources:

National Greenhouse Gas Inventory, 1990, 1995 & 1999 Australian Government Department of Climate Change

2005 Residential Energy Consumption Survey, US Energy Information Administration

Rule 1: Pick the Low Hanging Fruit

Its easy to get excited about the bleeding-edge gadget-end of eco-house design. Solar photovoltaics, thermal phase change materials, home automation, in-house fuel cells and other enviro-toys help us to shout our green credentials from the rooftops and still play with the coolest technology.

And that’s OK if you’ve got the dollars to spend on it.

But it’s not where the real action is in energy efficient design. In fact, concentrating on this stuff while ignoring the fundamentals – the flow of heat, light and electricity through the everyday materials of your home – is throwing money away for minimal ecological benefit.

The trick is to start with the easy, effective changes; the things that will give you the maximum impact for the minimum cost, risk and commitment. In fact, some of the most effective changes involve the smallest investment, and start paying you back almost immediately. This is what we mean by “Picking the low-hanging fruit”.

The benefits of this approach are obvious and immediate. Here’s an example:

Some time ago, we were approached by a homeowner who was looking at installing a roof-mounted solar panel system to fully offset his home electricity usage. His electricity bills were substantial, and a solar system with the capacity to offset them entirely was well out of his budget

A quick review of his home revealed (amongst other issues) 110 50w halogen downlights cluttering his ceiling. Assuming a conservative average of 3 hours on every night, that’s about $940 on his annual electricity bill for halogen downlights alone.

Just replacing his 50w globes with 35w IRC halogens (same light output and quality) at a total cost of about $900 would save about 1806 kilowatt-hours per year – that’s an annual saving of about $280. (He’d save even more replacing them with compact fluorescents.)

Compare that with that a 1.5kw grid-connected solar system costing about $12,000 (including the federal government rebate) which only generates about $233 worth of power over the course of a year (that’s a payback period of 60 years).*

That’s right – an investment of $900 on everyday-tech light fittings saved more electricity and greenhouse pollution that $12,000 of solar technology.

If this homeowner had spent his $12,000 on solar power, without upgrading the efficiency of these and other basic items, every single watt of power generated from the sun would have been used to power a ceiling packed with unnecessarily (and expensively) greedy downlights.  Instead, we recommended that he spend less than 10% of the cost to make up the difference through simple, off-the-shelf efficiency measures.

I don’t want to knock solar photovoltaics. We’ve designed several buildings fitted with them, like the Wistow Smart Farmhouse in the picture above. But if you don’t sort the simple things first, you’re paying serious money to waste the energy you generate with them.

So what are the simple things? Watch this space.

*Costing information www.citipower.com.au