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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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Ventilation: MVHR and high winds

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  1.  
    • CommentAuthorchuckey
    • CommentTimeDec 1st 2015 edited
     
    Where I live, at 250m on an exposed site its a lot more windy then average. So how do "proper" MVHR systems handle the increase and decrease in pressure within the building without losing too much heat. Do they use hinged flaps or similar or some sort of flow regulating chambers?
    Frank
    • CommentAuthortony
    • CommentTimeDec 1st 2015
     
    No, the bellows effect should be taken care of by the heat exchanger automatically.

    The house though if it is insufficient lunar tight might be a seperate problem
  3.  
    Posted By: tony...lunar tight...

    Now that's what I call a pressure test! :bigsmile:
    •  
      CommentAuthorfostertom
    • CommentTimeDec 1st 2015
     
    He means lunar tic
    • CommentAuthorSprocket
    • CommentTimeDec 1st 2015 edited
     
    I don't know about heat but if I switch off the MVHR then the CO2 level in our building is generally a little lower and falls more quickly when it is windy. I've been assuming this is just the small amount of leakage through the building fabric though.
    •  
      CommentAuthordjh
    • CommentTimeDec 1st 2015
     
    Posted By: chuckeyWhere I live, at 250m on an exposed site its a lot more windy then average. So how do "proper" MVHR systems handle the increase and decrease in pressure within the building without losing too much heat. Do they use hinged flaps or similar or some sort of flow regulating chambers?
    Frank

    Why would they need to do anything?
    • CommentAuthorringi
    • CommentTimeDec 1st 2015
     
    You should have the inlet and outlet on the same external wall, exposed to the same wind speed.
    • CommentAuthortychwarel
    • CommentTimeDec 1st 2015
     
    I am also on a highly exposed site, I have both the intake and exhaust mounted under the eaves about 2 metres apart on the East (downwind wall) and have never noticed any issues with gusting in the system, even when sitting in the loft next to the unit (where you can hear any variation in fan speed)
  9.  
    As per tychwarel but on the upwind wall - no probs. Just like 2 people pushing on a swing door with the same force.
    • CommentAuthortony
    • CommentTimeDec 1st 2015
     
    Not quite as when wind blows the pressure inside can be different to outside making both ducts either suck or blow.
    •  
      CommentAuthorfostertom
    • CommentTimeDec 1st 2015
     
    But if the house is more or les airtight, it's got nowhere to suck or blow to. In that case wind merely buffets internal pressure up and down, doesn't alter the fan-created suck vs blow differential in the ducts.
    • CommentAuthorCWatters
    • CommentTimeDec 1st 2015
     
    I can't say I've noticed any dramatic changes in air pressure indoors when the wind blows. Our inlet and outlet are on the downwind side.

    Just don't put the intake downwind of the boiler flue if you have one.
    • CommentAuthortony
    • CommentTimeDec 1st 2015
     
    Does the house get colder when it is windy than when it isn't!
  14.  
    Posted By: tonyNot quite as when wind blows the pressure inside can be different to outside making both ducts either suck or blow.
    For sure - technically.....but I imagine you are way past the decimal point in terms of l/sec. Equally I guess it is true that if you warm up the house air is expelled through both inlet and outlet too. But I don't think it is helpful to consider either effect.
    •  
      CommentAuthordjh
    • CommentTimeDec 2nd 2015
     
    I seem to remember that a force 6 is equivalent to 50 Pa or something like that. Gusts may be 35% of the average speed, so we're only talking about variations of 16 Pa or so even at the input to the duct system.

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