Re: [EnergyPlus_Support] Re: Thermal Bridge

["Jean Marais jeannieboef@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>]

You could calculate it. Assume a delta T of 1Kelvin, calculate the energy moving over the surface area with the surface to surface u-value of the layered construction. Then add the energy transfered over the length of the psi joint. Finally divide the sum of the energy transfers by the area of the surface to get the derated u-value of the wall. Then decrease your insulation layer until the desired derated u-value is achieved.

As Dave points out, software can do all this for you, but I find doing it once by hand can bring some insight and help understanding with more complex questions, like what is up with the air film resistances and how do they feature in all of this. And how to understand rated u-values and actual u-values.

I also "got on top" of these kind of questions by making spreadsheets for myself. Now I can check the software occasionally which is good to do to keep them on their toes!

On 24 May 2016 10:07 pm, "gauravciitr@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

 

Hi,

Thank you for the reply. 

Is there any relation between phi and u value which can tell me how much % do I have to derate the existing U value?

Maybe not any specific relation but any standard what people follow in the industry?

Like % do I have to derate when phi is 0.03 W/m2K

 

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Posted by: Jean Marais <jeannieboef@xxxxxxxxx>

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