I should know by now when I have to answer my own questions.
Funny things happen when you have to make a two dimensional window frame flat for an E+ calculation. I have a typical thermally broken aluminum frame about 50mm
tall by 150mm wide for which THERM calculates a U-Value of about 7 w/m2-K. E+ wants a U-Value for something flat that is 50mm wide without air films. The THERM air films are 26 w/m2-K exterior and 3.29 w.m2-K interior for a total U-Value of 2.92 w/m2-K for
just conductive air films. (This means I could do better with no frame?) So there has to be a lot of radiant heat loss to boost the frame up to 7 w/m2-K heat loss calculated by THERM. Now what has to happen is the E+ frame conductivity has to be very large
(or black hole negative) and apparently it defaults to maximum of about 500 w/m2-K (no air films).
Along the way with THERM/WINDOW we get center of glass U-Value and edge of glass U-Value. E+ now calculates center of glass internally. THERM gives us an edge
of glass U-Value from which a ratio of center to edge is calculated for E+. WINDOW also passes other glass properties along so E+ can internally calculate absorptions, reflections, and such.
What is horribly confusing is if you use a standard thermally broken frame from the WINDOW library as a base line check, the U-Value passed to E+ is around 50
w/m2-K, and one would think a modern thermally broken frame could do a lot better. The WINDOW library frame is apparently an older ASHRAE calculation that probably should not be used at all any more. (And if you have a truly low, THERM U-Value for a frame,
WINDOW passes a value less than 500 w/m2-K to E+.)
So the most important bottom line is that changing to high performance window frames does not impact the window frame heat loss calculations in E+ at all. The
only energy difference frames would make in E+ is if the frame area is reduced. The only other place some differences manifest themselves is in the edge of glass heat loss associated with a THERM calculated thermally improved frame.
So now if you want to calculate a single glazed baseline to see the performance difference of films or multiple glass layers, you will hit another wall. All
the aluminum frame single glaze (and several other frame types) I have calculated loose heat from the frame to the edge of glass. This makes THERM calculate and edge of glass heat loss that is less than the center of glass heat loss, a no no by the imposed
rules of E+. The work around is to edit the THERM results imported to WINDOW to make the edge of glass equal to the center of glass and let the rest come out in the frame wash, but the one dimensional frame heat loss is probably questionable.
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
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From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Friday, November 03, 2017 4:22 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] LBNL Window IDF Problem
Okay, we're on the same page. The last time I was doing this was with v7.2. I was checking how to reverse engineer a window with European rating conditions so that WINDOW shows the correct results using EU ratings, switch to NFRC ratings
(check how much SHGC and U-values differ for interest sake) and then export the IDF code from WINDOW for e+.
I checked values with a spreadsheet to follow if the edge of glass parameters were sane. Everything checked out okay.
I had used Therm as a pre-process only if no values were available for the frame. Also then I didn't get crazy values.
Something is going wrong in your THERM calculation. I would focus there.
Am 02.11.2017 1:30 nachm. schrieb "'Edward G. Lyon'
eglyon@xxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>:
The procedure is to model window frames and glass in THERM first, bring the results into WINDOW and then make a window in WINDOW. One of the reports you can generate is direct .idf text for E+, though I used to use the reference file input. I used to have problems with single glaze windows which I could work around. Turns out that there is often sufficient heat loss from the frame through the edge of glass to make the edge of glass look less conductive than center of glass. (too much brain power behind programming and not enough calculation experience) This problem is different and seems to be related to any frame system you model yourself.
I’m trying to reinstall version 6 and try again�have had several issuees with the 7 recently�
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 faxFrom: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Thursday, November 02, 2017 8:16 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] LBNL Window IDF Problem
I always did THERM first and used those values in WINDOW. Are you doing it the other way around?
2017-11-01 23:45 GMT+01:00 'Edward G. Lyon' eglyon@xxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>:
We are using LBNL WINDOW 7.5 and THERM 7.5 to generate .idf input for windows in EnergyPlus (as we have done numerous times before with other versions of the program). In WINDOW we have reasonable values for glass and frame conductivity, but when we export an .idf using our THERM frame calculation we get a value of 500 w/m2-K for frame conductance (ok, sometimes it is 499.999969). Using any of the default WINDOW frame entries returns a reasonable frame conductance value in the .idf.
Anyone else experience the same or know where to find a solution or know who better to ask?
Ned Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
| Engineering of Structures and Building Enclosures
41 Seyon Street, Building 1, Suite 500
Waltham, MA 02453781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com
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