If I recall the ASHRAE numbers correctly, R-19 (6 in. fiberglass) in 6 in. metal stud (uncompressed) 16 in. on center is a 50% reduction. I usually run my own
THERM or HEAT simulation to determine U-Values rather than take the published values because spacing and stud thickness varies a lot and the published values do not always account for head and sill conditions…
Ned Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Thursday, February 25, 2016 6:42 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] RE: Materials U-Value Calculations in E+
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"
On 2/25/2016 7:39 AM, 'Edward G. Lyon'
eglyon@xxxxxxx [EnergyPlus_Support] wrote:
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
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com
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: "Edward G. Lyon" <EGLyon@xxxxxxx>
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