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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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    • CommentAuthorgravelld
    • CommentTimeJun 27th 2018 edited
    A common criticism of MVHR for retrofit is the difficulty and disruption of installation, particularly when the house is being lived in when installation takes place.

    In the case of dwellings with unused space (e.g. a loft) I wonder if a hybrid solution is achievable? Install ducted MVHR to the first floor, running the ducts in the loft, and maybe single room units in the ground floor.

    Anyone heard of this, is it possible to "balance" such a system?
    • CommentAuthorgyrogear
    • CommentTimeJun 27th 2018 edited
    Agreed, but then again, lots of other jobs cause disruption, such as painting and decorating, or renovating a bathroom, laying wood floors etc.


    Perhaps by associating a whole house fan with the MVHR, one might get some heat transfer in the rest of the home (via stairwell etc.)

    Edited for a more angular reply...

    I suspect that MVHR is associated with "need for big holes in the house"
    Where circumstances prevent knocking (or making) of big holes in the house, IMUO (in my uninitiated opinion...) I would go for another solution such as PIV (positive input ventilation) preferably combining it with a low-level intake, a ground-source HEX, and low-level exhaust. The problem being to get the optimal airflow path (i.e. no short-circuiting...).

    PIV avoids the need to make big holes in the internal structure - the air path is natural, through doorways and circulations etc. (assuming that habitants are not locked in by doors). Perhaps a minimum of transfer grilles etc. will be required.

    In the less-friendly case of an upstairs PIV, the top intake (of cold air) would be warmed in an (insulated) loftspace and the difficulty is then getting this downstairs, which means fighting the natural buoyancy of warm air... Not to mention (according to one's circumstances...) fighting the tendency of teenagers to sit behind closed bedroom doors, which becomes, effectively, not only a problem of society, but of aeraulicists...

    • CommentAuthorRobL
    • CommentTimeJun 27th 2018
    I expect that you will have unexpected stack/wind ventilation occurring. Either of these will give extra loss to the MVHR.
    We have only a few vents, for ease of diy retrofit - 3 inputs upstairs, 1 downstairs, 1 exhaust upstairs & 1 downstairs. All pipes are big at 150mm diameter, so the flow is slow & quiet, and balancing is easy (dominated by the mvhr unit).
    I think as long as you have decent gaps under doors, a room with 1 person in is generally ok without a vent.
    Our vents are placed so that most of the house is in an airflow from one to the other.
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