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    All passivhaus designs I have seen use whole house mechanical heat recovery ventilation systems.

    Has anybody heard of any designs using single-room heat recovery ventilation units?

    Advantages might be simplicity (although maybe the wiring makes this not the case, but if you're already wiring the room as a new build...) and fire safety.

    Disadvantages might be expense and inefficiency, although I can't see in principle any limit to how cheap a single room unit can be. Indeed the mass-market nature of them suggests they could be very cheap indeed and I have seen some that claim high efficiencies.

    I also don't know whether having a hole through the shell in each room effectively makes a cold bridge or not. Obviously it would if the unit were switched off, but when it's running?..

    This design could be particularly good in countries like the UK where electrical skills are obviously available but ducted ventilation or heating systems are rare in the domestic market.

    Seems like one could also have single rooms adapted to passivhaus standards, or build passivhaus extensions to existing dwellings in this way.
    • CommentAuthorMiked2714
    • CommentTimeOct 26th 2009
    We have one single room MVHR in each bathroom. The do the job and we're happy, but there's no way you'd want them in bedrooms as they do rumble rather. They aren't as efficient as the more conventional units either.
    • CommentAuthorbrig001
    • CommentTimeOct 27th 2009
    I would think that having a hole in each room would cause problems when it was windy, especially if they were positioned on opposite sides of the house. This would lead to a pressure imbalances and therefore heat loss. The one facing the wind would have a net flow into the house and one on the opposite side would have a net flow out of the house. As I understand it, a whole house system has the inlet and outlet on the same side of the house so that the wind puts equal pressure on both therefore not causing heat loss.

    Hope that makes sense,
    • CommentAuthordocmartin
    • CommentTimeOct 27th 2009
    where did you see the requirement to put inet and outlets on the same side of the house? I have not seen this as mandatory during extensive reading. When using earth or ground pipes to preheat the outlets would often be widely seperate; during discussion of the problems with ground pipes the length and resistance to flow are often mentioned but not opposing directions to the wind.
    • CommentAuthorbrig001
    • CommentTimeOct 28th 2009
    Hi docmartin, can't honestly remember, it may just have been a diagram I saw. Thinking about it, with whole house HRV, wind will simply affect the rate of ventilation, not the heat loss - assuming the house is airtight. Hmm, looks like I was wrong there. Sorry about that, I must have read more into a diagram than I should.

    I think I am right on single room HRV though.

    • CommentAuthorarthur
    • CommentTimeOct 28th 2009 edited
    Sounds like a good idea in bathrooms instead of the standard extractor fan - how wasteful are they of heat. What would the power consumption of one of these be for a small bathroom? And how long would you need to run it after a shower?
    We used this product for a few PassivHaus renovations http://www.inventer.de/en/References/Ongoing_Projects/site__284/
    and would like to use this one when it goes into production http://www.breathingwindow.org/
    • CommentAuthordocmartin
    • CommentTimeOct 29th 2009 edited
    the planning process for the MVHR system I have installed in my own home required me to identify the "crossover airflow paths" in the building; typically hallways and landings. Adequate spaces under doors(or even grilles) provide a route for the air to circulate from supply valves to extract. I suspect that a room with a single MVHR unit would be prone to calm zones of poor air change increasing with distance from the unit. Martin
    • CommentAuthorRobinB
    • CommentTimeOct 29th 2009
    I have to have fire doors to all habitable rooms. When shut these will block the "airflow" paths - is there any type of fire-check grill that can be fitted in a fire door or do I just keep the doors open most of the time? Is there anything about this in the regs?

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