Campus Chilled Water vs 90.1 Baseline Chiller

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Hello, all.

I'm working on a DD-level Energy Model, and am having some trouble with
the results.

My Design Building will use campus chilled water, and campus steam.
I've modeled those per the instructions in the TRACE User Manual.

My Baseline Building is a System 7, and is therefore modeled with a
chiller (screw-chiller >150, <300 tons), and a boiler.

The overall cooling loads for the two alternatives are:

Baseline: 548.1 tons

Design: 393.1 tons

On the PRM Summary, however, the Space Cooling energy is coming up at:

Baseline: 765.0 (10^6 Btu/yr)

Design: 3659.7 (10^6 Btu/yr)

It seems to me there should be an energy savings with chilled water,
over the chiller. At any rate, it seems strange to me that there'd be
an increase of Cooling Energy of 5 times, to meet a smaller load.

Might anyone have any suggestions?


Martin Snarski LEED(r) AP

Snarski, Marty's picture
Joined: 2011-10-01
Reputation: 0

When you are modeling purchased chilled water, you are basically setting
up a chiller with a COP equal to one. So if you are comparing a
baseline building with a chiller (COP equal to 4.9), you can expect the
purchased chilled water energy to be 4.9 times greater than the
purchased chilled water energy for an equivalent cooling load.

Steve Mettlach

smettlach's picture
Joined: 2010-12-21
Reputation: 0

Per the attached document (see link), for LEED, you will have to do a
Step 1 model where you compare your building design to the baseline with
both as purchased chilled water so you wouldn't be comparing a chiller
to purchased chilled water. Then, in the Step 2 model, you would
compare your chiller (campus system, district cooling, whatever) to an
ASHRAE chiller. This amends Appendix G.


Beaton, Christine's picture
Joined: 2011-10-01
Reputation: 0

In particular, pay attention to the type of air handling equipment you have to use in the step 1 model. In some cases, it will be different than what Ashrae 90.1 directs you to do. For example, in the step 1 model, the appendix G amendment may direct you to use FCUs but in the step 2 model, Ashrae 90.1 may direct you to use PTACs. Just make sure you read every word of the document that Christine referenced.

+ Jimmy Stevens | |

Jimmy Stevens's picture
Joined: 2011-10-01
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