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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorpiersadler
    • CommentTimeDec 19th 2011 edited
    Has anyone read Sue Roaf's article on mechanical ventilation (MV) in the latest issue of GBM? This article suggests MV (including MVHR) is a health risk and that these systems are energy hungry, without acknowledging the energy benefits of airtightness and heat recovery. Taking the implications of the article to their logical conclusion, we should ditch measures to make buildings highly energy efficient eg Passivhaus and huddle round heaters in cold leaky buildings instead. The health study from the Netherlands looked at 'perceived' health impacts from MV and whilst it may be valid, I don't think we can throw away Passivhaus based on a single study.

    The article cites the deaths of 25,400 older people in the UK from cold in winter 2010/11 and asks whether whole house MVHR would have been their salvation. I think in airtight buildings the answer is probably 'yes' and in well insulated airtight buildings definitely 'yes'.

    The clear failing in this article and apparently in the thinking which supports it is that it appears to be based on a prejudice against MV without addressing the reasons why it is used. Without mentioning airtightness, without mentioning Passivhaus (where it is a requirement), the article is worthless.

    My request is for better informed evidence based debate in GBM. I'd like to know what other members think, particularly on the issue of Mechanical Ventilation. I am not a particular supporter of MV, although I recognise that airtightness has a part to play in energy efficient buildings and that Passivhaus has a serous role in the future.
    I have not read the article mentioned, but Sue Roaf has produced a number of articles in the past which cast unsubstantiated doubt on the Passivhaus approach & draw on experience in other countries without proposing detailed workable solutions for the UK.

    I can understand the desire to design houses which don't rely on "artificial" ventilation. However, any alternative needs to stack up with MVHR from an energy conservation point of view &, before any conclusions can be drawn, needs to be prototyped on real houses & monitored through at least one heating season.

    There will always be a market for "Eco Homes" which feel "Green" & I think Sue Roaf's approach will appeal to those who don't ask to see the heat loss calculations. However, there is a solid scientific basis for the Passivhaus approach which cannot be just swept away with a load of "hot air" & that provides an invaluable guide to those trying to understand the real energy consumption of their proposed home.

    • CommentAuthorRobinB
    • CommentTimeDec 19th 2011
    Coul Fi-Wi be the happy medium between the two approaches?
    • CommentTimeDec 19th 2011
    I plan to build to passive level or close and my plan includes MVHR of some description both for finance and health reasons. My only concern with Fi-Wi is that it is only located in one room, Viking house says this is not a problem but I can see the logic for extract and input in different rooms. Perhaps a duct could be run from the input or extract to another room?
    • CommentTimeDec 19th 2011
    I too find Roaf's work less than satisfactory. This article appears to be mainly an attempt to sell her new book. Finding an author declaring "an important new book" about her own work seems a little bit over the top.

    She refers to a 'Technical Report 14' that apparently supports her views and makes it sound independent. She completely fails to mention that she is an author of this too! It's perhaps worth noting that the report is focussed on older properties and says "Although the proposed heating strategy cannot reduce the energy consumption to the levels expected of newly built houses with modern standards of insulation, it can be used together with other technical upgrade measures". It also recommends greater ventilation.

    She refers to an article that is not yet published, making it very difficult to judge. She also fails to mention that she is on the editorial board of the journal in which the article will appear. Again, hardly independent. When summarising criticisms apparently made in the article, she doesn't distinguish between those inherent in the systems, and those caused by faulty installation or operation and maintenance, which are quite different problems to my mind.

    So I don't feel able to take an informed view of her article. But the points above, together with a whole sequence of non-sequitur and apparently rhetorical questions throughout the article mean that my instinctive emotional reaction to it is pretty negative.

    I join piersadler in requesting a better standard of journalism in the Green Building Magazine.
    • CommentAuthorwookey
    • CommentTimeDec 20th 2011 edited
    Like the rest of you I wasn't terifically impressed, but then I know she is a fan of natural ventilation and has been for many years. I understand she is an authority in that area (and has written some good stuff in the mag about natural ventilation in arabic countries, and erm, something else I forget).

    I don't like the power consumption of MVHR either, and especially if you take a low-energy aproach anyway, it's not hard to fit one badly and use more energy than you did before (although very likely with better air quality in exchange). With modern kit this problem seems greatly reduced. (I think RobL said his is running at under 5W much of the time - that really isn't a problem).

    I don't see how you can make really low-energy buildings without it, but then not all buildings are passivhauses(en?), and it clearly makes sense in some circumstances: the Cambridge company Breathing Buildings is doing very good work halving the energy use of schools and offices by fitting smart natural ventilation. Yes it's nothing like as good as a passivhaus, but it's a hell of a lot better than the aircon +open-windows they had before.

    So I think there is a place for her approach, although it would have been better to make the comparison without suggesting that there is 'no scientific evidence' behind the MVHR/MEV approach.
    • CommentTimeDec 20th 2011
    I worked for a while in a building with natural ventilation (it had been designed so that there were large convection "stacks" internally). It worked very well and as you say wookey, is probably better for a non-passivehaus in terms of energy use.

    What is beginning to annoy me is the way that MVHR seems to be being advocated by manufacturers as an energy saving measure for ordinary houses. I very strongly suspect that it's no such thing for the majority of houses in the UK, that are generally far from being adequately air tight.

    Personally I'd like to see whether it would be possible to make a zero energy passive MVHR system, the snag being to find a way to make it work acceptably under all weather conditions. I may have to settle for just using PV to offset the power used by the fans.
    • CommentTimeDec 20th 2011
    How about this for a compromise:- www.passivent.com/downloads/hybrid_ventilation.pdf
    • CommentAuthorRobinB
    • CommentTimeDec 20th 2011
    Just read joe90's link. A nice idea. A bit surprised they see no advantage in running the heat recovery side of it when the outside temperature is above 9 degrees.
    It's an interesting solution. My main concerns would be routing the additional extract ducts (which must run vertically to the roof) & making it airtight in winter mode. One of the advantages of MVHR is that it only requires two external wall penetrations. This solution requires one for every room; an extract vent for each wet room & a supply vent for each habitable room. Putting a summer bypass on the MVHR & a PV panel on the roof to run the fans seems like a neater, more robust & easier to make airtight solution.

    • CommentAuthorpiersadler
    • CommentTimeDec 21st 2011
    Thanks djh for recognising that my initial post was really about the standard of journalism rather than mechanical versus natural ventilation.
    I think there is probably a lot to be achieved by replacing air conditioning with natural ventilation in many cases and I also agree with JDHarris that MVHR in buildings which are not sufficiently airtight is a very poor choice, but whatever the issues in the debate, lets have more evidence based and balanced arguments in GBM.
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