do you know where i can refer the u values for air gap?
any guide book that i can download from?
Do you know what is the u calue for 127mm air gap
3 Answers
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Thermal conductivity for air varies based upon its temperature. It is usually listed as about 0.025 which is in watts per meter per degree C. So I believe the conductivity for 127 mm would just be 0.127 x 0.025.
You will need to crunch the numbers to get the units you need.
However, U value is based upon conduction; with air there will also be convection, since it is not a rigid insulator.
See links below.
Good luck.
Bill
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U Value Of Air
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For the best answers, search on this site https://shorturl.im/axkve
If you have access to the ASHRAE volumes, they are a good resource. Otherwise, you might check the attached link.