Ned, others,
There are two effects going on with R-19 insulation between metal studs:
1) compression of R-19 insulation within the 3.5" cavity, thus reducing its R-value to 18
2) 2-D heat flow due to the metal studs, which is a much bigger effect with the studs acting like radiator fins.
I don't have an exact number in my head, but I recall that the net effect was to degrade the R-value by a huge amount, like 30-40%.
Joe
Joe Huang White Box Technologies, Inc. 346 Rheem Blvd., Suite 205A Moraga CA 94556 yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx http://weather.whiteboxtechnologies.com for simulation-ready weather data (o) (925)388-0265 (c) (510)928-2683 "building energy simulations at your fingertips"
One thing to remember is that the assembly and not the materials determine an effective U-value. R-19 batt insulation between metal studs may be half the R-value, and that is what you should be using for the energy model. If you select a wall system in design builder that includes thermal bridging elements, it should push the effective insulation value to the energy model.
Ned Lyon, P.E. (MA, WV)
Staff ConsultantSIMPSON GUMPERTZ & HEGER
781.907.9000 main
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617.285.2162 mobile
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From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Thursday, February 25, 2016 8:24 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Materials U-Value Calculations in E+
Hi everyone,
I need some help to understand how is the calculation of u-value material in energy plus.
Someone has a spreadsheet that calculates according to the material specifications?
I ask this because I use the design builder to enter the building elements, and saw that the U-value is not the same in EnergyPlus report.
I don't know how energyplus calculate this.
Thanks for all.
Best regards,
Ivan Mezzacapa
Cushman & Wakefield
Energy Efficiency and HVAC Coordinator
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Posted by: Joe Huang <yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx>
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