[Equest-users] Thermal Blocks/HVAC Systems for LEED Credit

[Bishop, Bill]

Michael,
 
If it were me, I would not try to model multiple zones as a single
thermal block if the zones are served by different-sized systems.
Different system sizes imply the zones are not thermally-similar.
 
If you have created thermal blocks of stacked apartments that ARE served
by the same sized systems, then I think you are justified in modeling a
single system for that zone with the combined capacities of all the
systems and using the efficiency of those systems. But I agree with the
reviewer that you should model each different "stack" with the size and
efficiency of the identical systems in that stack.
 
The 90.1 User's Manual goes into detail about how/when to create thermal
blocks, but I can't find where it describes how to combine systems, so
this is just my opinion.
 
Bill
 
William Bishop, PE, BEMP, LEED(r) AP | Pathfinder Engineers & Architects
LLP
Mechanical Engineer
 
 134 South Fitzhugh Street                 Rochester, NY 14608
T: (585) 325-6004 Ext. 114                F: (585) 325-6005
wbishop at pathfinder-ea.com           www.pathfinder-ea.com
<http://www.pathfinder-ea.com/> 
P   Sustainability - the forest AND the trees. P 
________________________________

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of M.
Shields
Sent: Tuesday, March 29, 2011 3:36 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Thermal Blocks/HVAC Systems for LEED Credit
 
Hi All,
 
I have modeled a multifamily building for LEED which uses a variable
refrigerant flow system.  In the building each stack of apartment's
heating and cooling is provided by one unit, but the stack next door is
provided by a different unit.  The efficiency is determined by the
outdoor unit and varies slightly by size, which is not the same for all
apartment units.  I have modeled several apartments as one thermal block
and I had calculated an overall system efficiency by doing a weighted
average based on system size.  My reviewer has commented that per
G3.1.10a I need to use the individual system size and efficiency for
each system.  I am wondering if they will accept a weighted average by
thermal block instead of an overall system average.  It seems quite
clear under G3.1.9 that modeling multiple apartments on the same wall is
perfectly acceptable.  Do you need to have multiple systems serve each
zone?  I did not think this is possible.
 
Any thoughts/experience with this situation would be greatly
appreciated.
 
Thanks,
Michael
 
____________________________
Michael Shields
Facility Strategies Group, LLC
1012 Market Street, Suite 307
Fort Mill, SC 29708
Phone: 803-493-4507
Fax: 803-548-2511
Email: mshields at fstrategies.com
 
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