Interpreting a model for a full building analysis w Comcheck

[Peter Aaron]

I have built a model of a masonry cavity wall and window assembly and have managed to get it to run, after fixing a number of geometry glitches.  There is a deep return of the masonry at the window jamb with the window set back from the face of the wall.  The projected X and projected Y of the exterior wall are each 16 inches and the interior wall projected X is 16 inches and the Y is 3 inches.  The U value for the interior X wall and the exterior X wall are almost identical.  For the total length of exterior wall the R is about 30 while for the total length of the interior it is about R15.

Question is how to interpret these for a whole building analysis with ComCheck.

[Robin Mitchell]

Peter

 

What does ComCheck want for input ? Is it the U-factor / R-value of the wall including the window ? Or does it separate out the window U-factor from the wall U-factor ?

 

Here is how I would suggest you break up the U-factor calculation if you are using one THERM model. If you need to input a UA value, then you would multiple the U-factor of each tagged THERM section, then multiply that times the area of that type of wall, and then sum them together to get a total wall UA (if that is what you are trying to calculate). The places where you change the U-factor tags are where the isotherms  become parallel. You will see that is where I separated the Window Frame / Wall U-factor from the regular Wall U-factor – you want to find the point in the cross section where the window frame is no longer affecting the heat flow / temperatures. In terms of how to break up the Window Frame from the Center of Glass, you should look at the NFRC Simulation Manual on our website – in particular look at page 6-35, which shows how far up the glass to start the Center of Glass U-factor tag.

http://windows.lbl.gov/software/NFRC/SimMan/NFRCSim6.3-2013-07-Manual.pdf

 

 

***

Robin Mitchell

Windows & Envelope Materials Group

Lawrence Berkeley National Laboratory

--
You can view the THERM forum online at: http://windows.lbl.gov/software/THERM/forum
---
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.
For more options, visit https://groups.google.com/d/optout.

[Peter Aaron]

Hi Robin,

Thank you for your reply.

I attach also a typical wall section w/o window.  ComCheck wants the value for each element and the total area of each element.  So I could use the U value for the window alone and the value for the wall alone but that is not actually what is happening with the deep return modeled here and would give a heavily biased result.  We also want to make this perform to the highest level possible, given the space and budget we have to work with. 

So if I understand what you are saying, what you are suggesting is that the overall façade is divided into 3 portions, middle of glass, frame (including jamb return) and wall.  The value for the jamb/frame would be a weighted average of the masonry return and the window frame in the X using the length in the x plane of each. (corresponding to the points where the lines are parallel) Or this can be gotten out of the model by specifying a "custom Length"?

I will look at the Simulation Manual  6-35 and see what it says. 

If I have further questions I will post again.

Thank you

Peter Aaron