Assemly Effective Thermal Resistance Higher than Insulation Value of Assembly

Tristan Mullock

unread,

Mar 9, 2021, 6:18:26 PM3/9/21

to THERM

Hello,

version THERM 7.7.10

I am repeatedly (but not consistently) getting results of higher than expected thermal resistance of assemblies using steel framing through insulation. The values are so extreme that they are in excess of the nominal insulation value of the assembly. The temperature isotherms make sense with expectations.

For this specific case, I have R25 of fiberglass batt insulation achieving an effective rating of R36 while being bridged by a steel z-girt at 4' on center. The insulation properties are Conductivity 0.0266 (imperial) and Emmisivity of 0.9 covered by a layer of steel sheet and minimal thermal break at the steel framing member.

Please help!

tlmu...@gmail.com

unread,

Mar 9, 2021, 6:27:37 PM3/9/21

to THERM

metal test section.png

Robin Mitchell

unread,

Mar 9, 2021, 6:54:06 PM3/9/21

to tlmu...@gmail.com, THERM

I think it will be hard to debug this without the actual THERM file. Please provide it if you can.

Robin

--
You can view the THERM forum online at:
https://groups.google.com/g/LBNL-THERM
---
You received this message because you are subscribed to the Google Groups "THERM" group.
To unsubscribe from this group and stop receiving emails from it, send an email to LBNL-THERM+...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/LBNL-THERM/da9d5491-dd6c-424c-8947-4bfb0ab8311an%40googlegroups.com.

--

Robin Mitchell

Building Technology and Urban Systems Division
Energy Technologies Area
Lawrence Berkeley National Laboratory

Tristan Mullock

unread,

Mar 9, 2021, 7:22:48 PM3/9/21

to Robin Mitchell, THERM

For some reason, I was getting an error message when trying to upload earlier.

metal framing test.THM

Shaun Martin

unread,

Mar 11, 2021, 12:03:36 PM3/11/21

to THERM

Hi,

I have struggled with this exact problem recently. One solution that worked was to change the interior boundary condition from comprehensive to simplified.

Shaun

tlmu...@gmail.com

unread,

Mar 11, 2021, 5:06:02 PM3/11/21

to THERM

Thanks Shaun. That worked perfectly!

yal...@gmail.com

unread,

Mar 13, 2021, 12:08:22 AM3/13/21

to THERM

Hello. Both the interior and exterior boundary conditions are set to Auto Enclosure. Therm cannot calculate the value when both are set this way. When Auto Enclosure is used on the inside the outside radiation needs to be set to Blackbody or simplified.

6.0 Btu/h/ft2/F is the standard outdoor film coefficient should be set to simplified.

1.46 Btu/h/ft2/F is the standard indoor film coefficient for walls should be set to simplified.

In the file indoor boundary is set to vinyl/wood and is probably close for a wall but really meant for window frames.

Yalin

Reply all

Reply to author

Forward