[BLDG-SIM] Appendix G, Window wall ratio for the baseline

Peter Alspach peter.alspach at arup.com
Thu Sep 6 17:22:26 PDT 2007


Simple answer is that your client is incorrect. If the 100% CD documents
show that the WWR is 27% then that is the design. what if the architect
started at 35%, 29%, 65%??? All irrelevant.
 
You should be able to show savings if you still use a very high
performance glass and/or shading as the ASHRAE baseline glass
performance decreases with decreasing WWR - that is where you get
leverage.
 
Peter

________________________________

From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Dana
Troy
Sent: Thursday, September 06, 2007 2:47 PM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Appendix G, Window wall ratio for the baseline


Hello All, 
 
 I have a question that pertains to ASHRAE 90.1-2004, Appendix G, Table
G3.1, No.5, which details modeling requirements for calculating proposed
and baseline building performance for the building envelope.  I'd
appreciate any thoughts you all might have on this LEED modeling.  
 
 We are currently working with a client on a building with a window-wall
ratio of 27%. The WWR was reduced from 40% by the architect in order to
obtain higher energy cost savings. When building the baseline model,
Appendix G states: 
 
 "Vertical fenestration areas for new building and additions shall equal
that in the proposed design or 40% of gross above-grade wall area, which
ever is smaller..." 
 
 Our client believes that since in the schematic design, the WWR was
over 40% and was then reduced to below 27% for energy efficiency
reasons, the baseline building should be modeled with a 40% WWR to show
these savings due to architectural design. 
 
 I understand that the proposed design stated in Appendix G refers to
the building that is going to be built, or the 100% CD drawings.
However, our client wants to see the definition of "proposed design"
from ASHRAE that explicitly states what the proposed design is. After
researching for a while, I found Addendum A, which states on page 4 of
the Addendum: 
 
 G3.1 Proposed Design Model. The simulation model o f   
 the proposed design shall be consistent with the design documents, 
 including proper accounting of fenestration and 
 opaque envelope types and areas; 
 
 and: 
 
 G3.6 Building Envelope. All components of the building 
 envelope in the proposed design shall be modeled as shown on 
 architectural drawings or as built for existing building envelopes. 
 
 This still is not enough to accurately define the proposed design. I am
sure that you might  all agree with me on the interpretation of Appendix
G, but does anyone know where I can find a solid definition of what the
proposed design is? I have searched the CIRs on the USGBC website and
came up empty handed and don't know where else to go. ASHRAE said a
formal interpretation request could take upwards of 6 months, so that is
also out of the question .  
 
 Any help would be greatly appreciated.  
 
 Thanks, 
 Dana Troy

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