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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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Heating and cooling: MVHR & Open Windows on hot nights

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    We are two weeks into living in our new house. The first few days were very hot internally (I fear we have a bit too much solar gain), but once the MVHR was turned on the internal temperature regulated itself a lot better and we were trying to keep the windows closed (which is what I understand you should do with MVHR). Generally this was working ok, but I did notice that two of us sleeping in the bedroom overnight definitely heated up that one room quite a bit.

    Last night in London was very warm (as was the rest of the country I think). The MVHR, even on night time purge, didn't seem to be cutting it so we threw open the windows to get a cooling cross breeze coming through the house.

    Interested to know what other people with MVHR did last night / will be doing over the next few days. Do you open your windows? Or should the MVHR be able to cope?
    • CommentAuthortony
    • CommentTimeJul 19th 2016
     
    Opening windows is fine, we do it often,

    Re solar gain, shade Windows externally, hang sheets over them any thing then think of more permanent solution later
  3.  
    I live in Italy, currently 32 deg outside and will get down to 19 tonight - MVHR off for most of the summer, windows open at night only with BIG fan in roof extracting to ensure we get a breeze. But downstairs in the self contained half basement apartment, I leave the MVHR on all summer (windows open at night) and the 'frost' control turned from 5 deg to 25 deg.
    • CommentAuthortychwarel
    • CommentTimeJul 19th 2016
     
    I only have my MVHR on during the heating season and used windows for summer ventilation.
    • CommentAuthorGreenfish
    • CommentTimeJul 20th 2016
     
    " we were trying to keep the windows closed (which is what I understand you should do with MVHR)"

    What on earth gave you that idea? Open the windows!!!

    MVHR provides fresh air (replacing the stale stuff polluted with C02, VOCs, moisture and smells) with minimal heat loss during the heating season, but it is not an air conditioner. It will not keep your house cool in hot weather even in summer bypass mode (no longer heat exchanging), it was not designed to do that.
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      CommentAuthorfostertom
    • CommentTimeJul 20th 2016
     
    But doesn't PH calc summer overheating (or avoidance) assuming the MHRV is on and windows closed? How could PH calc that with MHRV off and windows open - much too uncontrolled to be able to guarantee?
  7.  
    It all depends on the temperature difference between indoors and outdoors. Yesterday evening it was 32C outside and 24 inside. The windows stayed firmly closed until near bedtime, when the temperatures were rather closer. Then open all night to get the cooler night air into the building, and closed again (together with south facing window curtains) this morning.
    • CommentAuthorringi
    • CommentTimeJul 20th 2016
     
    You can’t stop overheating when it is too hot outside without a cooling system. At best you can delay the overheating for a few days, by then, in the UK, the rain is back….
    • CommentAuthorCWatters
    • CommentTimeJul 20th 2016
     
    We have MVHR and in summer we open the windows any time it's colder outside.
    • CommentAuthorGotanewlife
    • CommentTimeJul 21st 2016 edited
     
    Posted By: dimengineerYesterday evening it was 32C outside and 24 inside. The windows stayed firmly closed until near bedtime,


    Posted By: CWattersWe have MVHR and in summer we open the windows any time it's colder outside.


    Exactly right. Here in Italy this is the way one lives in the summer. Plus, I have a max 3m3/s centrally mounted extractor for when it is cooler outside than in - that way I don't have to rely on the weather for a breeze! Also the avg internal temp is a little lower as a result of my high mass house being cooled from within as well as from outside.

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