[Bldg-sim] District Thermal System

May Xu may.xu at hok.com
Thu Aug 7 19:39:20 PDT 2008

Thanks so much for all your replies. They help me a lot. Thank you!

-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of David S
Sent: Friday, August 08, 2008 12:02 AM
To: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] District Thermal System

It seems that the intention here is that if a credit is taken for an
exemplary LEED building for energy efficiency, it will have to overcome
district energy system (DES) inefficiencies if they are present.  But at
the same time, you are able to get the minimum two EAC1 credits, to some
degree regardless of how bad the DES performs - so not excluding most
projects, but limiting the options for those projects with inefficient
infrastructures.  This recognizes some of the constraints that a campus
project might encounter.

Likewise an efficient DES that may have efficient equipment,
cogeneration, heat recovery or other efficiencies will benefit the LEED
project and the team is rewarded for having built onto this type of

Step 1:  Building stand-alone scenario - for EAP2 compliance as well as
documenting up to two EAC1 credits.  In both cases will be purchased
from district energy systems for heating and cooling as appropriate.
This I think was the discrepancy between Fred and Julia's posts - the
USGBC document states on page 8 that the actual prices are to be used,
so it would include the overhead and profit components for a commercial
DES.  For campus situations without a "price" you must calculate the
equivalent value and it isn't specified if this includes the overhead

If your building used DES for only one source, then the other source
would be modeled as proposed with the baseline equipment per App G.

So as Fred mentioned, it will be DES vs DES, chiller vs chiller, or
boiler vs boiler, etc.

If only pursuing EAP2 and two or fewer EAC1 credits (and achieving
them?), stop here.

Step 2:  Aggregate building - for pursuit of additional EAC1 credits -
here the DES will be modeled for electricity and fuel usage, and
compared to a building with baseline heating and cooling equipment per
App G.

The key point of the text is "virtual on-site equipment representing
upstream" systems.  So not exactly that system, but representing the
LEED project's share of that system.

Putting some numbers to a cooling plant for example purposes, the
intention is not for you to model a 500 ton load building being served
by a plant with four 5,000 ton chillers.  Neither is the intention that
you should model the other buildings making up the 19,500 ton

The simulation programs are generally able to use efficiency
calculations based on the total plant, but imposed on a theoretical
smaller "virtual" plant serving the load of the new project.  This is a
reasonable approximation to the share of the plant energy for the new
project assuming the cooling/heating loads are following the profile of
the DES in general.  The virtual 500 ton chiller will have capacity
specified to match the LEED project's demand, but with the efficiency
curves and EIR of the existing 5,000 ton chillers.

Obviously the capacity of everything in the plant would have to be
adjusted, not just the chillers and boilers - include pumps, cooling
towers, etc.

There is a statement about Step 2 only providing up to four additional
EAC1 credits over Step 1, up to a maximum total of ten credits (like
normal).  But my interpretation of the document is that even if you
documented six EAC1 credits in step 1, you can only claim two of them
unless you unlocked that potential by proceeding to Step 2.  Is this
everyone else's interpretation also?

Hope this helps!


> -----Original Message-----
> From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-
> bounces at lists.onebuilding.org] On Behalf Of Craig Simmons
> Sent: Thursday, August 07, 2008 8:47 AM
> To: bldg-sim at lists.onebuilding.org
> Subject: Re: [Bldg-sim] District Thermal System
> Hi May,
> I interpret the update differently. It does not state that the
> must
> be the same, only that the efficiencies must be the same. I believe it
> expected that you create a virtual onsite plant sized to replace the
> normally covered by the DES. The virtual plant must have the same
> efficiencies as the actual plant, but not the same capacity.  In
> you must implement a calculation or approximation to account for
losses in
> the distribution system. I believe that the statement "the DES central
> plant
> itself shall always be modeled as a total, entire unit" is to prevent
> model from combining the virtual plant (to cover DES loads) with any
> supplementary onsite plants that may exist. I don't think it is
> that you model the DES at its actual capacity.
> Anyone else have a different opinion?
> Craig Simmons
> The Green Engineer, LLP
> Sustainable Design Consulting
> 50 Beharrell Street
> Concord, MA 01742
> t: 978/369-8978
> craig at greenengineer.com
> www.greenengineer.com
> Please consider the environment before printing this email. Thank you.
> -----Original Message-----
> From: May Xu [mailto:may.xu at hok.com]
> Sent: Tuesday, August 05, 2008 10:20 PM
> To: Jeff Haberl; bldg-sim at lists.onebuilding.org
> Subject: Re: [Bldg-sim] District Thermal System
> Hi Jeff,
> Thanks, I found many useful information there, it is a very good
> resource! However, I didn't get relative answers regarding my
> which is about the simulation rule updated by USGBC recently about the
> district thermal system. Could anyone give me any suggestions?
> Thanks a lot!
> May
> -----Original Message-----
> From: Jeff Haberl [mailto:jeffhaberl at tees.tamus.edu]
> Sent: Tuesday, August 05, 2008 11:36 AM
> To: May Xu; bldg-sim at lists.onebuilding.org
> Subject: RE: [Bldg-sim] District Thermal System
> May:
> The Laboratory has spent quite a bit of time modeling the thermal
> on the Texas A&M Campus with good success. Unfortunately, we ended up
> using some rather complex, interacting loop models with chiller
> staging algorithms, etc.
> We have a number of papers and thesis on this at our web site
> "www-esl.tamu.edu" look under publications.
> Jeff
> 8=! 8=) :=) 8=) ;=) 8=) 8=( 8=) :=') 8=) 8=) 8=?
> Jeff S. Haberl, Ph.D.,
> P.E.............................jhaberl at esl.tamu.edu
> Professor......................................................Office
> Ph: 979-845-6507
> Department of Architecture.......................Lab Ph: 979-845-6065
> Energy Systems Laboratory.......................FAX: 979-862-2457
> Texas A&M University..............................77843-3581
> College Station, Texas, USA.......................URL:
> 8=/ 8=) :=) 8=) ;=) 8=) 8=() 8=) 8=? 8=) 8=) 8=)
> ________________________________
> From: bldg-sim-bounces at lists.onebuilding.org on behalf of May Xu
> Sent: Mon 8/4/2008 4:53 AM
> To: bldg-sim at lists.onebuilding.org
> Subject: [Bldg-sim] District Thermal System
> Dear All,
> I'm now working on a project using Districted Heating System provided
> a municipal system. The municipal system is working for a very large
> areas providing steam for about hundred buildings. And my building is
> one of them.
> According to the latest update issued by USGBC
> (https://www.usgbc.org/ShowFile.aspx?DocumentID=4176), the modeling
> be implemented by two steps. My question is about Step-2 (Aggregate
> Building/DES Scenario).  In step-2, the energy source of Proposed
> Building is virtual on-site chiller representing upstream DC system.
> document also issues "The DES central plant itself shall always be
> modeled as a total, entire unit." My understanding is that it requires
> to model the central plant with the full capacity that is able to
> provide heating for all of buildings in whole district. However, if
> doing so, the energy consumption of the proposed building may be quite
> quite high, since it includes the energy consumption of the whole
> heating plant!! But my building is only one of the 100 buildings that
> are heated by the central plant.  It is weird and  I don't think it is
> what USGBC asked for. Does anyone know what shall I do for the
> building in Step-2?
> Thank you.
> May Xu,  LEED(r)AP
> Project Engineer - Sustainable Design
> Suite 3705A, Ciro` s Plaza,
> 388 Nan Jing West Road,
> Shanghai, 200003, PRC
> Tel:  (86 21) 6334.6181 ext. 2230
> Fax: (86 21) 6334.6182
> www.hok.com <http://www.hok.com/>
> www.hokasiapacific.com <http://www.hokasiapacific.com/>
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