Thursday, 29 September 2011

But what about all the energy used to make the house?

"Toilet seats from the UK, 250 kg of window from Germany, special visits from foreign manufacturers... are you going for some kind of embodied carbon record?" PJ just wrote.

I remember talking to someone from the Green Party a few years ago about environmental costs, and saying how great it would be if there was some measure of how bad things were for the environment, so we could make the right decisions.

"There is," he said. "It's called money."

And to a large extent he was right.

Recently, Japan has introduced Eco points, whereby you get points for buying energy efficient products. You can then spend these points on... anything you like really. Beer even. Not sure how energy efficient beer is, but that is not the point.

A student said he'd just bought a new TV, and got lots of Eco points for it. Apparently, the bigger the TV, the more Eco points you get. A bigger TV means more energy consumption, so really you should be getting less Eco points for a bigger TV and more for a smaller one, and in this case the money you spend may be a better indication of ecological strain. If you're comparing TVs of the same size, of course the Eco points will help.

Even with a Passive House, the units are all measured per unit area of floor space, so a palatial one-person passive house could use a lot more energy than a one-room home for a family of seven. 

But money doesn't always count.

I remember being told that cars consume ten times more energy in their manufacture than in their normal lifetime, so buying a new car, however energy efficient it is, is likely to be worse than carrying on using an old car. What Car claimed that 80% of the life-cycle energy of a car comes out in its use, with 15% in manufacture and 5% in its scrapping. But perhaps What Car have a vested interest in people buying new cars. According to an article by Mike Berners-Lee in the Guardian, the amount of energy used in manufacture and use is around equal, half and half, but perhaps he has a vested interest in people buying his book on carbon footprints.

Anyway, embodied carbon is an important issue, and the University of Bath has produced an inventory of carbon and energy per kilogramme of various materials, which they will email you if you ask nicely. As well as looking at Carbon Dioxide emissions, they look at other greenhouse gases and convert them to CO2 equivalents. A lot of research and thought has gone into their work, and they even have a special excel file that will calculate the carbon footprint of concrete depending on the mix used. 

For example, it gives the following figures in kg of carbon dioxide per kg of various different kinds of insulation:
polyurethane (flexible) 4.06
polystyrene (high impact) 2.76
glass wool 1.35
rock wool 1.05
wood wool (board) 0.98
cork: 0.19 
But you'd have to drink a lot of wine for the last one, and it's not as good an insulator as the others. After all the wine it may not matter. 

It also gives figures for timber framed and aluminium framed windows at 12-25 kg CO2/kg and 279 respectively. So aluminium frames are not only going to consume a lot more energy in their lifetime, they also consume a lot more in their manufacture. In a lot of cases, though, you have to look at the weight of materials used. For example, aluminum is lighter than wood, although not ten times lighter.

With a little more energy of the human kind on my part and a little more support, it would have been great to balance the embodied carbon in the building with the energy use of the building's lifetime, but the main focus has been on consuming as little energy as possible over the house's lifetime. This is perhaps a foolish thing to do in Japan, where the life expectancy of a building is less than a quarter of a century. On the other hand, if what we are doing can make a difference to the way people build in Japan, then it may be a good thing. 

It may of course backfire, as people copy the mistakes and collateral details rather than the main points. I've heard that the Nara local government are sending their wood to Germany to be built into windows there, as Japan does not have the window manufacturing technology, then sent back to Japan so that they can have windows made of Japanese wood. Not sure how that comes out on the carbon calculator. Also not sure whether trees have a sense of national identity, but that is another issue.

In many cases back in our house, we looked at choices where there is a clear increase in cost which results in a clear decrease in energy use, and the payback period can be calculated.The pay back on the solar panels is around 8 years. There was one issue with the windows that meant a pay back of around 50 years, which is around the lifetime of the windows and, on financial terms, not worth it. In terms of carbon, the choice was between paying for cuttting edge technology and expertise against paying people to pump fossil fuels into fires for the next 50 years, so the carbon calculator gives a clearer answer.

Even if you are just looking in financial terms, the budget of the project will affect how much you can actually spend now, because saving money in the future is no use if you don't have enough to spend now. Reality bites.

I think we looked at reducing the amount of heat we would lose by raising the window frame specs to "Passive House Certified", which sandwich insulation in the frame, but the pay back would have been more than their life time. Increasing the amount of heat coming in by changing the glass in the south-facing windows to high-g led to an extra cost with a much quick payback.

What we have tried to do, anyway, is to optimise the building for lifetime energy efficiency, but work needs to be done in both areas, and our understanding of the carbon footprint is deepening the whole time. This should show what is possible, and where we want to go. The bigger question is how we get there.