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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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Energy Assessment: How many air changes per hour for a healthy building?

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  1.  
    • CommentAuthorRobinB
    • CommentTimeApr 27th 2010 edited
     
    Got a bit confused here. Just about to order MVHR unit. My SAP calcs (see below) say air changes per hour 0.24 and general internet search suggest 4 air changes. What have I got wrong? Thanks for help!

    Dwelling volume 532.58m2
    Infiltration due to chimneys, fans and flues 0.04
    Pressure test, result q50 3.00
    Infiltration rate 0.19
    Number of sides on which sheltered 2.00
    Shelter factor 0.85
    Adjusted infiltration rate 0.16
    Ventilation : balanced whole house mechanical with heat recovery
    air throughput (air changes per hour) 0.35
    efficiency in % allowing for in-use factor 75.65
    Effective air change rate 0.24
    • CommentAuthorRobinB
    • CommentTimeApr 27th 2010
     
    Just found this from earlier discussion.... How can my SAP calcs be so low, or am I comparing apples and pears?

    Posted By: tonyMy house has just been set up at 1.36 air changes per hour overall

    lounge 2 ach, en-suite 5 ach, kitchen/diner 2.5 ach

    should I be happy or should I be concerned that my ventilation heat loss will be too high?

    any give me ideal ach for a house.

    my system is fully adjustable and controllable by the user -- me.
    • CommentAuthorsydthebeat
    • CommentTimeApr 27th 2010 edited
     
    *edit*
  4.  
    Be careful you specify the pressure the ACH figures are measured at. In a blower door test, a 50Pa (de)pressurization is used which will multiply the normal pressure ACH figures by around 20. CSA F326 specifies ventilation requirements in terms of litres per second (per occupant) rather than an ACH figure. See http://www.nrc-cnrc.gc.ca/eng/ibp/irc/ctus/ctus-n15.html

    BTW, in the previous post it looks like Tony's figures are @50Pa not normal pressure.

    Paul in Montreal.
  5.  
    PHPP expects the average to be at least 0.3ac/h under normal usage conditions. Higher than this under boost, and possibly less than this during periods of low occupation/activity.

    Building Regs Part F (http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADF_2006.pdf) has a set of instructions on how to calculate the required ventilation through an MVHR system.

    Your figure seems a bit low, but not so far off.

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