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Calculating window installation Psi values for PHPP

  • 09-12-2010 9:02am
    #1
    GreenTech
    Closed Accounts Posts: 26 ✭


    Hi All,

    I've been working quite a bit lately with therm software in calculating thermal bridges to plug into PHPP. The standard thermal bridges are straight forward enough... well when I say straight forward enough I mean after a lot of hair pulling I've mastered it. When it comes to the installation Psi value for windows I'm wondering if anyone can back up my way of calculating this as I cannot find any documentation on how to calculate it using therm or any other similar software package. I figure that the PHPP already accounts for the u vlaue of window frames and the Psi value of spacers independently in the software. Given that the frame window data accounts for the heat loss through the window frame and glass etc. I have simply calculated the heat loss through the jamb including any insulation overlap on the frame but excluding the window frame itself. Any surfaces in contact with the window frame are Adiabatic. This is then compared to a wall section of same length but without the jamb ie. straight wall with Adiabatic boundaries to both ends. Seems to give me Psi values very close to what would be expected but I can't find any documentation to back this up at the minute. I would appreciate if anyone with any experience in this area could let me know how they have calculated this Psi value or maybe point me towards a relevant document with a calculation method which is acceptable by PHI?:)

    Thanks for reading!


Comments

  • #2
    sinnerboy
    Closed Accounts Posts: 5,433 ✭✭✭sinnerboy


    GreenTech wrote: »
    I cannot find any documentation on how to calculate it using therm or any other similar software package.

    You need to buy BR 497 “Conventions for calculating linear thermal transmittance and temperature factors”


  • #3
    GreenTech
    Closed Accounts Posts: 26 ✭GreenTech


    Hi Sinnerboy,

    Thanks for the response.
    BR497 is useful but doesn't really have the answer I'm looking for. Using an Adiabatic boundary condition where window frames exists will give me the Psi value at a jamb/head/sill for instance. Is this acceptable to use as the 'installation Psi value' in PHPP win type worksheet? or is there a different method of calculating the installation Psi. I am of the opinion that this is in fact the installation Psi as the PHPP software takes into account the window frame dimensions and u-value which accounts for heat loss through the window frame so I'm thinking that the installation Psi value is simply the thermal bridge within the wall element caused by installing a window. I just cannot find any documentation to back this up!


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