I agree ‘ventilation is an important issue and deserves more attention than it generally receives’. A building super-insulated and super-airtight won’t support human habitation without the addition of air. There are many constructional ways to achieve Passivhaus certification but only one ventilation solution – MVHR – which is the basic problem with Passivhaus.
You state with certainty that MVHR is necessary in the UK but this is far from proven. I’m assuming your evidence is the Carbonlite Information Paper ‘Comparing energy use and CO2 emissions from natural ventilation and MVHR in a Passivhaus house’ that was contested by Arup within the RIBA Sustainability Group when published in 2009. A very limited case was investigated in the paper, whereas Arup figures suggested that MVHR could not be justified on energy grounds in the South of England. Most certainly the Carbonlite report cherry-picked the most favourable numbers to make its case, for example 87% heat recovery (and how long will that fan efficiency last?) rather than the PHPP default of 75%. To my knowledge the AECB have produced nothing of certainty since?
Passivhaus is concerned with energy saving and comfort to the exclusion of the fact that homes are occupied by people of different lifestyles and culture. We hear daily on the news how the culture of Germany differs from other parts of Europe. Most certainly the home maintenance usual in Britain is at a remove from that usual in Germany. The recent Good Homes Alliance report ‘Ventilation and good indoor air quality in new homes’ found that MVHR filters may need changing every three months1. I suppose housing associations could have filter-change teams roaming the streets but for privately rented or owner occupied housing the likelihood of maintenance being adequate is zero.
Passivhaus exponents always argue that if the MVHR isn’t working problem, occupants can just open a window, and that mechanical ventilation is just like a boiler - it requires servicing. If however a boiler isn’t working one feels cold but human perception of indoor air quality is a lot more fallible. This is a worry – that at a time when allergenic illness is at an all time high and the basic causes are little understood2, we are proceeding with MVHR, a technology with so many problems.
My own particular interest is in retrofit which has far greater potential to help achieve the UK’s need for 80% carbon reduction than does new-build. The Energy Saving Trust reported at Ecobuild3 that there have been problems with all the MVHR installations for Retrofit for the Future (the majority of their retrofits incorporated MVHR) including those attempting to achieve Passivhaus standard. Your article is written as if we are within an ideal world, and Passivhaus certification standards most certainly are close to ideal. But beyond control are the VOCs off-gassing into houses with largely unknown consequences for health. As the NHBC points out, to outlaw the offending materials is at present impossible4 - dry air is the least of our worries - the design ventilation rate is a healthy and safety issue.
In Scandinavia, where the science of indoor air quality was developed, at trade exhibitions there are prominent displays for duct cleaning equipment. MVHR has ducting on the supply side of the system; the least gap in the insulation/ductwork will be a gathering point for condensation and pathogens that will be undisturbed for the lifetime of the building, because there is no likelihood in England that ductwork will ever be cleaned.
As Shaun Fitzgerald wrote just recently5 ‘…The Passivhaus standard’ involves the inclusion of a mechanical ventilation system. I don’t understand what is passive about this’. In the case of retrofit MVHR is a virtual non-starter because of the extreme difficulty of accommodating the ducting within existing 2-storey houses, which makes the Enerphit standard an irrelevance. As the Institute of Sustainability FLASH reports suggest6 what is required is a hybrid system that will run passively most of the time but with fan-backup. Passive stack has the advantage of ducting on the extract side only but given its limitations occasional fan power is required, however in the sheltered conditions of the south of England how many times a year will the fans run?
There are passive systems with heat recovery: the BeDZed PSHR, the Lunos system in Germany, French-made ‘supply air’ windows, using secondary glazing to pre-warm incoming air, humidity/pressure controlled passive stack + heat recovery etc. These may not have the supposed efficiency of MVHR but Enerphit is unaffordable anyway. The only way to meet the 80% carbon reduction is to achieve 60% through physical measures – insulation etc – and enlist behaviour change amongst householders (plus renewables) to achieve the rest. Householders will of course expect that the systems they are learning to use won’t be counter-intuitive - air should come from windows not out of a hole in the ceiling7.
MVHR is the market solution; it will make money for manufacturers who will be selling a lot of kit. That doesn’t necessarily mean that the market solution is the right solution for people. Unfortunately the manufacturers’ trade organisations are such a forceful lobby, and because what was once the UK’s national and non-commercial building research centre has virtually ceased building research, alternative solutions are hard to test. The only available test facilities are those owned by the manufacturers who have a vested interest in going mechanical.
I thought when the Passivhaus Trust was established that the intention was to adapt Passivhaus to UK requirements – climate and culture. Instead the output of the Trust is in terms of ‘myth busting’ and promoting Professor Feist’s UK tour as if for a visiting rock star, is Passivhaus now the ‘only true faith’? What you should be doing is promoting debate rather than acting as a mouthpiece for the mechanical equipment industry. For example, are Passivhaus standards - adopted so far only by ardent enthusiasts - really appropriate for incorporation in the building regulations?
We have a habit in this country of adopting skewed rather than holistic agendas that only later reveal unforeseen side effects. The high-rise flats of the 1960s, built for speed but before long mouldy and uninhabitable, are a case in point. 50 years later the list of technical measures for inclusion within the Green Deal makes no mention of the words ‘domestic ventilation’8. It’s all going to end very badly!
1 Good Homes Alliance ‘Ventilation and good indoor air quality in new homes’ November 2011, page 76.
2 NHBC ‘Mechanical ventilation with heat recovery in new homes’ January 2012, page 24.
3 Alex Stuart ‘Post occupancy evaluation and performance – first winter results’.
4 ibid 2 page 34.
5 Dr Shaun Fitzgerald ‘A help or hindrance – Dr Shaun Fitzgerald questions the use of PassivHaus design in the UK’ Architects Choice, March 2012 page 47.
6 Institute for Sustainability FLASH guide 7 ‘Improving the building services’ September 2011, page 7.
7 see Macintosh and Steemers ‘Ventilation strategies for urban housing lessons from a POE case study’. Building Research and Information ( 2005) 33(1) pages 17 – 31.
8 Department of Energy and Climate Change ‘What measures does the Green Deal Cover?’ May 2011.