[Bldg-sim] ASHRAE 90.1-2004 Purchased Chilled Water

Andy Stone andy.stone at bdsp.com
Fri Oct 10 07:43:06 PDT 2008

I received an off-list reply to my query which pointed me towards the
following LEED document:



The document describes an alternative procedure for cases where you have
district thermal energy schemes (it covers both heating and cooling).  


Hope that helps,




From: Dan Russell [mailto:danr at engineeringinc.com] 
Sent: 10 October 2008 15:33
To: Andy Stone; bldg-sim at lists.onebuilding.org;
bldg-rate at lists.onebuilding.org
Subject: RE: ASHRAE 90.1-2004 Purchased Chilled Water


I have a similar scenario although mine is on the heating side.  In my
case the proposed building is using purchased heat via a low-temp
geothermal water source that can be purchased from the local District.
The baseline is required by App G to be VAV w/ reheat using design
supply hot water temp = 180 deg F.  The geothermal source is 110 deg, so
it can't be used in the baseline scheme with standard hot water heating
coils.  This situation is different than Andy's in that using the
geothermal source results in a tremendous cost savings to the owner.
The proposed system will use Water-Water Heat Pumps to take about a 65
degree temperature drop out of the 110 deg source.  The cost of the
source is based on gallons usage, with no regard for heat transfer.  The
rate schedule is set to be equivalent to the cost of natural gas
assuming a 20 deg temperature drop.  So in essence, every degree the
system can take out past 20 deg is free heating energy, which I'm hoping
the modeling protocol allows credit for.


So, I am interested if there is any insight out there on what to do when
the baseline and proposed systems utilize separate utilities.




 Dan Russell, EIT 




From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Andy Stone
Sent: Friday, October 10, 2008 4:49 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] ASHRAE 90.1-2004 Purchased Chilled Water


Hi all,


I'm doing a LEED EAc1/ASHRAE 90.1-2004 Appendix G calculation where the
building is served by a district cooling scheme and the basecase
building is serviced by PTHP (ASHRAE 90.1 table G3.1.1A), i.e. the
basecase building is uses electrically powered DX coils compared to
purchased chilled water coils for the proposed building.  


The problem I have is that the price per kWh of chilled water is very
close to the local price per kWh of electricity, which means that the
cooling energy cost of the proposed building ends up much larger - for
the PTHP system 1kWh of electricity gives something like 3kWh of
cooling, but the same money only gets 1kWh of cooling from the district
scheme, which makes it virtually impossible to get any LEED EAc1
credits.  Has anyone else encountered this issue?


Thanks for your help,



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