18 Apr 2007

Passive Passive Houses

Spent the day in Nottingham at the School of the Built Environment, talking with its head, Prof Brian Ford, and two of his colleagues, Rosa Schiano-Phan and Mark Gillott. They had contacted me about my PassivHaus musings: it seems I am not the only one who has had a few doubts about whether this standard is all that it is cracked up to be.

In particular, they wanted to talk about low energy performance standards in warm (i.e. Mediterranean) climates. They have been part of a group of institutions, funded by the EU, which have been looking into creating a sort of PassivHaus-lite standard which would be better suited to Spain and Italy and, just possibly, to the UK and Ireland as well. Nottingham has a particular interest in natural ventilation techniques and they are worried that the German PassivHaus standard shuts out all but mechanical ventilation with heat recovery (MVHR) solutions. I share their disquiet. There remain a number of doubts as to whether MVHR is the best solution for all housing. What doubts?

• It’s mechanical: it requires a fan to operate: it therefore uses power.
• As it’s mechanical, it will require servicing. This may or may not get done. And it will of course break down from time to time.
• This raises one or two health issues. As PassivHaus is nearly airtight, indoor air quality is dependent on fans. What happens if the fans stop? Will anyone notice? Could it even be dangerous?
• People have raised concerns over the health implications of drawing input air through long lengths of ducting. In an ideal world, the ducting should be demountable for cleaning purposes but such a requirement doesn’t form part of the PassivHaus standard and seems likely to be ignored.
• In short, there is concern that the PassivHaus standard has got the balance wrong between carbon reduction and personal health.

But the Nottingham crew have further misgivings. They reckon the maximum space heating requirement figure, the famous 15kWh/m2/annum (the very nub of the PassivHaus standard), was actually too generous for warm climates. It seems to have been set with Germany or southern Sweden in mind: in the Mediterranean you simply don’t need that much heating, or to put it another way, you don’t have to build to PassivHaus standards to get such a predicted annual heat load. In fact, the cooling load is far more significant in the Mediterranean climate and they think it’s a much better approach to incorporate natural ventilation techniques, which can keep the air fresh in winter and cool in summer.

How does this relate to the UK? Here we are in mid-April with the daily maximum temperatures well into the 20s, and having just experienced nothing more than a one-week winter. It’s hard not to conclude that the climate we are experiencing has already changed significantly. The question is why are we getting obsessed with a performance standard (i.e.PassivHaus) which is a) not entirely applicable to our climate and b) over-prescriptive about U values, air tightness and ventilation techniques? They are worried that the PassivHaus standard will somehow morph its way into our SAP ratings as the only way to build a zero-carbon house and that other more compelling options will be effectively shut out.

To this end, the Nottingham group are working up an alternative low energy standard, a naturally ventilated version of PassivHaus (maybe that’s a Passive Passive House), which they think is better suited to warm climates and, just possibly, to the UK as well. They are planning a launch event and a very active debate about the pros and cons of PassivHaus in September (18th and 19th).

The other really interesting thing they are up to is building a series of experimental houses on the campus, to be known as the Creative Energy Homes. They already have one experimental house built on site seven years ago; now they will be erecting another six. There will be public access for some time and it’s sure to be a big draw. Pictured here is the Stoneguard C60 steel framed house, as it looked this afternoon in the balmy sunshine.

No comments:

Post a Comment