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

Dan Russell danr at engineeringinc.com
Fri Oct 10 07:33:26 PDT 2008

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

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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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