Wednesday, April 18, 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.



Anonymous Anonymous said...


I am a sceptic currently getting to grips with the PH standard. I attended the recent PH conference in Bregenz and was looking forward to a bit of debunking. However I came away impressed.

I have resisted MVHR for all the reasons and prejudices outlined but in hot and cold climates, once insulation and detailing is sorted, ventilation is where all the energy gets lost.

In addition, as we limit ventilation air to save energy we risk all the health issues mentioned.

It will be interesting to see what Nottingham come up with but meanwhile I can correct a few misunderstandingsfrom my limited knowledge:

1. The PH concept can be adapted to different climates. I have a short paper 'First;Steps What Can be a Passive House in Your Region with Your Climate' by Dr Feist, sorry I can't find the link but its a pdf.

MVHR is recomended where external temperatures are often below 8C or above 32C. Obviously 'often' can be defined by energy modelling.

2. Yes mvhr uses power but the best kit with DC fans and efficient heat exchangers saves far more (primary) energy than it consumes when used in appropriate climates (see above).

3. All buildings should be airtight. Leakage is a defect that can lead to rot and mould. Ventilation is something else. PH buildings have opening windows. Passive ventilation doesn't work in all conditions and trickle vents get shut when it's windy to stop drafts then are left shut (this is what I have and it's a real juggling act). Using MVHR allows really good ventilation without loosing all the heat. In cold weather this will reduce humidity - less mould, dust mites etc.

4. The PH people seem very aware of dirty duct issues and claim it has been dealt with. Clean air ducts are kept short but I can't comment further as I don't know.

5. It is my understanding that human health and happiness is fundamental to the PH concept since it is all about making buildings that are a joy and so are replicated.

Whatever is built needs to deliver truly low energy use (120kW.h/m2/y primary energy is the PH backstop target) and more healthy conditions.

I've no reason to defend the PH concept and would have liked to have seen more people in the audience shouting 'bollocks' as would have happened at an AECB conference, but I am keen to correct predjudices.

sorry about my spelling

Nick Grant

8:33 am  
Blogger Mark Brinkley said...

Thanks for the perceptive comments, Nick. I think the PassivHaus Institute need to do a better job of answering their critics and explaining their theories. It may be that all the issues being raised against the PH standard are already addressed, but it seems to me that there is still a large gulf in understanding.

8:56 am  
Anonymous Anonymous said...

To Nick:

Thanks for shining a light on this topic which is often misunderstood. Good explanation, especially point 5.

To Mark:

"The Passivhaus Institut need to do a better job of answering their critics..."

No, they don't. Their research is thorough, developed over many years, and is published. The Institut is not a hard-nosed commercial business and it doesn't sell houses. It has a limited budget, and tries to help other people achieve this excellent energy standard cost-effectively. They go out of their way to make their information and software packages available at low cost. Its success is now the basis for a wide-spread uptake of the standard.

The fact that most of that information is presently in German, is a reflection (unsurprisingly) of not only its origins, but also their workload - due to huge demand in Germany, Austria and many other counties which approach them directly. The continuous lack of UK government interest, coupled with our lack of language skills, means that the UK has lost out on this wealth of know-how and practical expertise.

Those who are really interested try to go and join in the annual bilingual Passivhaus conference.

If doubters want more information, then the UK must actively engage with the Passivhaus standard, and start translating - the onus is on us, not the Passivhaus Institut! The information is out there.

If the government was really committed to tackling carbon reduction, it should start promoting the passivhaus standard rather than spending more hype on its poor 'zero-carbon' concept. It could, for example, fund the AECB or the BRE to start the ball rolling. Or it could invite and fund the Passivhaus Institut to hold a Passivhaus conference here!

6:40 pm  
Blogger Mark Brinkley said...

Hopefully, this meeting in Nottingham in September will be a good place to air all these issues. The BRE will be represented, in the form of David Strong, and I believe that Bill Dunster is coming as well, so both sides of the MVHR debate should be represented.

11:11 am  
Anonymous Anonymous said...

Whilst not yet mainstream, even in Austria and Germany, I think professionals in those countries have been exposed to the methods and technologies for a long time.

I still hear people in UK saying low energy houses are unhealthy because of the mould and lack of air. My in-laws bungalow now has cavity wall insulation and PVC double glazing and yes it smells mouldy - perhaps this is why people get these ideas?

Our house is genuinely low energy although designed over 11 years ago before I had heard of PH and the only place we ever get any moisture is the bottom of some of the window glazing. this is why you need to go to triple low e etc in a PH, not just to save a few % of energy but to keep all the indoor surface temperatures high - its a comfort thing.

BTW I'd really like to see some robust debate of any real weaknesses in the standard as I have no reason to defend it.


9:43 am  
Anonymous Anonymous said...

What do the people at Nottingham think the UK is - a branch of the Cote d'Azur? It's not; it's a damp and reasonably cold climate with as much need for heating as say Vancouver or Amsterdam or Seattle, places which accept the need to build tight, ventilate right. But that's just southern England or Wales - Scotland is colder.

Such distortion by people who as I think someone said haven't read the German (or going even longer back the Canadian) literature simply tends to strengthen our reputation for being an eccentric offshore island!

11:00 pm  
Anonymous Anonymous said...


An interesting thread.

I too live in a very low energy house with MVHR and, like Nick, suffer a bit of mould round the bath and on a couple of windows, but no problems of any significance.

Is everyone clear that the AECB's CarbonLite Programme has three steps for bulding energy performance at its core - Silver, PH and Gold? We are about to publish the performance and prescriptive standards, along with several tools to help people achieve them in practice.

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