[bldg-sim] Curtain wall frames and fenestration area

[Azerbegi, Renee]

 Well, Mike, you are correct, the difference is small. I went ahead and modeled a two-story 25,000 sf office building in Denver with 50% window-to-wall ratio and low-e double pane windows. The effect of framing with individual windows versus one big window, with the same percentage frame has less than 1% difference in energy usage and cost.  The effect of shading, whether modeled as individual fins on small windows or one big fin for one big window does have about a 2.5% increase in heating usage, however this is offset by cooling reduction, so the overall difference is less than 1% in energy cost. This may have a different effect at different climates. I can email anyone interested the spreadsheet of results. 

Renee

-----Original Message-----
From: Mike Tillou [mailto:miket at etcgrp.com]
Sent: Monday, April 12, 2004 12:56 PM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Curtain wall frames and fenestration area


Has anyone actually done a comparison to see what sort of effect modeling the frame different ways has on the actual loads in the space.  I realize there is no panacea answer but I would be curious to know what the effect of modeling a single window with enlarged frame area vs actual window size and frame width is.  Is it a 5% difference or a 20% or .05%.  I am curious only because I have always assumed the difference was small and that there were more important (larger impact) modeling items to worry about.  
 
Please note that I am not trying to discount the importance of correctly modeling windows but trying to understand the overall impact different modeling techniques might have on output.    
 
Mike Tillou
etc Group, Inc. 
  _____  

From: postman at gard.com on behalf of Fred Porter
Sent: Mon 4/12/2004 10:48 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Curtain wall frames and fenestration area


Also, if you are using either of the detailed glazing models, the way Steve describes should better account for edge-of-glass effects. Dividing glazing up into lots of tiny little "panes," as some architects want, has an extemely delterious effect on the IGU overall U-factor, above and beyond the effect of the frame itself. If using the SC inputs, it might be instructive to run Window 5 on some similar configurations, to check the overall U-value with DOE2's output. (Noting where interior, exterior etc films are/aren't accounted for.)

If you want a pretty rendering for the client, I recommend a separate model, for presentation only. And then if trying to do daylighting calcs......;

stvgates at pacbell.net wrote:


The solution below can work, but does not take into account the effect of shading due to fins and overhangs.  For those windows, a better approach is to define one of the windows, together with its fins/overhang, and then use the window MULTIPLIER to establish the total number of windows on the wall wall.  If the overhang shades a significant portion of the wall, in addition to the window, then the overhang can be defined as a separate shading surface.

----- Original Message ----- 
From: Mike Tillou <mailto:miket at etcgrp.com>  
To: BLDG-SIM at gard.com 
Sent: Monday, April 12, 2004 7:44 AM
Subject: [BLDG-SIM] Curtain wall frames and fenestration area

Renee,
 
The easiest way to do this is to use a single window on each wall.  Calculate the percentage of window area that is actually frame and then adjust the frame-width to account for the increase.  You may end up with a window frame width that is 12 inches or bigger  (if the wall is large enough).  With a little ingenuity you can write some BDL code that will automatically calculate the window width, frame width and x position of the window on the wall so you don't get any cautions or warnings.  .  
 
 
 

Michael Tillou, PE
etc Group, Inc.
PO Box 749,  North Adams, MA 01247
Ph. (413) 458-9870   Mbl. (413) 652-1087   <http://www.etcgrp.com> www.etcgrp.com 
 

  _____  

From: postman at gard.com on behalf of Azerbegi, Renee
Sent: Mon 4/12/2004 7:44 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Curtain wall frames and fenestration area



Greetings,

I am modeling a high-rise building in eQuest which has a significant amount of fenestration as curtain wall. This curtain wall, like many curtain walls, has metal frames around many small panes of glass that make up the total curtain wall. My question is, how do you treat the frames and the fenestration area?  If I model each small pane of glass and add the exact frame, this would probably overwhelm DOE2 due to the huge number of small windows.  If I model the glass as one big window, then is it correct to just add the total width of the frame to each of these large windows? Also, some of these curtain wall panes have fins to complicate things, so if I do one big glass pane, then adding the fins would make huge fins on either side of the glass. If you have dealt with modeling curtain walls, as probably many of you have, please let me know how you have dealt with these issues.

Thank you,

Renee

Renee Azerbegi
RMH Group
303-239-0909x641


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-- 

Fred W. Porter

Senior Engineer

Architectural Energy Corp.

2540 Frontier Ave. Suite 201

Boulder CO 80301

email:  fporter at archenergy.com

fax: 303-444-4304



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