On Friday, I attended the debriefing session run by the DTI Global Watch Mission, which sent a small party to Sweden, Denmark and Germany in November. It was similar, in many ways, to the PassivHaus study tour, which I went on in February, but it was a longer tour looking at a wider range of low energy housing projects.
The general consensus was also pretty similar to that drawn by the PassivHaus study tour. In all three countries, they were looking at the same sort of things: a small number of exemplar projects, all with the emphasis is on pretty much the same features: massive insulation levels, air tightness, triple glazing, mechanical ventilation with heat recovery and a little booster heating to get things up to par. It’s a recurring theme: you’d be tempted to think that maybe they have the solution to the conundrum of how best to construct low energy housing.
However, there are subtle differences between the three national approaches. In no particular order, here are some of the notes and calculations I made, as a result of attending the session.
• 80% of new homes in Sweden are heated with electric heat pumps, of which over 60% are ground source heat pumps. Remember, Sweden has loads of hydro-electricity, so electric heating makes sense for them in ways it doesn’t in other territories. They use to prefer the cheaper air-to-air heat pumps but people found them noisy and the growth in the market is now happening with ground source heat pumps.
• In Denmark, 60% of homes have a supply of hot water pumped into the house from a district heating system.
• The Germans pay 50 cents (33p) per kWh for renewably generated electricity sold on to the grid. No other nation does this. Consequently, German roofs are covered in PV arrays.
• Micro Combined Heat and Power plant (CHP), fired by the Stirling engine, throw off one unit of electricity for every seven units of heat. You end up with far too much heat for optimal use. However, the next generation of fuel cell-based CHP, which should be commercially available by around 2010, should produce roughly equal amounts of heat and electricity. This should address the output issue, but at the moment fuel cell CHP is anything but micro: it requires a dedicated plant room.
• There is yet another low energy standard that was mentioned that I hadn’t come across before. The 3-litre house. This refers to the amount of heating oil required to provide space heating for each square meter of a house each year. 3-litres is reckoned to be the bees knees for renovations. 7-litre houses are something close to the building regs standard in Germany: in contrast, the PassivHaus standard is lower still, probably around 1.5-lts. This fascinating new take on a performance standard sent me scurrying off to my Excel spreadsheet which analyses our home usage. On this basis, I reckon ours is an 8-litre house! For a house built 15 years ago, that’s not too bad but I am not sure I should boast about it.
• The 2006 Part L building regulation for England & Wales indicates a space heating requirement or around 40kWh/m2/annum. I reckon that could be termed as a 4-litre house. Or maybe it’s nearer 5.
• Don’t say it too loudly, but we use another 4 litres per annum per m2 just to heat our domestic hot water. These extra litres are somehow overlooked from the standard.
• The Swedes, the Danes, the Germans and the Brits all seem to design homes with a 60-year lifespan. Quite where this 60-year figure came from, I have no idea. Why not 50? Or 75? How come everyone settled on 60?
• Having said that, only around 15,000 homes are demolished every year in the UK. That is one tiny number when compared to the 180,000 new ones built and the 25 million homes that currently exist. At that rate, it will take 1667 years before we manage to replace all the existing homes we have built, which is precisely 1607 years more than their design life. Does anyone foresee any problems building up here?
• The NHBC reckon that currently 47% of new homes being built in the UK are apartments. How long are they going to have to last?