District Thermal Energy in LEED

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Fellow Modelers,
I would greatly appreciate any answers and comments on formulating a submission and/or CIR.

I am working on a LEED project which is heated by steam from a coal fired plant and is subject to the USGBC's District Thermal Energy document https://www.usgbc.org/ShowFile.aspx?DocumentID=4176.
Should the baseline hot water boiler plant in the Step 2 analysis be:
A) a coal fired boiler with the proposed boiler efficiency since 90.1 does not address coal fired boilers,
B) a natural draft coal fired hot water boiler with an assumed code efficiency since 90.1 does not address coal fired boilers,
C) a natural draft gas fired hot water boiler with the code efficiency referenced in 90.1, or
D) something else?

Remember the metric is energy cost savings.

If you reread it, replacing the word 'coal' with 'trash', does your answer change?

Thank you,

Paul Riemer

Paul Riemer's picture
Joined: 2011-09-30
Reputation: 0

In the Step 2 model for the baseline, you DON'T use the same district
energy system used in the proposed. Instead, you use on-site boilers of
the type specified in ASHRAE 90.1 Tables G3.1.1A and Tables G3.1.1B.

Interestingly enough, this is a contradiction from what is stated in
paragraph G3.1.1.1 of 90.1, but USGBC has clarified their intention in
soon to be released updates of the DES Guide.

Seth Spangler, LEED(r) AP

Tiger06's picture
Joined: 2011-02-14
Reputation: 0

Seth, Sam, and Eric,
Thank you for weighing in. I should not have used the word 'plant'. So please allow me to restate my question.
I know the Step 2 baseline boilers are on-site, but what fuel type and what efficiency?

Appendix G prohibits fuel switching and I cannot find anything in the DES guide that counters that, so on one hand I think I need the same fuel type which means options A or B.
If I chose option A, I have no savings potential and just distribution losses so no heating side reason to do Step 2.
If I chose option B, I am choosing a code efficiency for a natural draft coal/trash fired hot water boiler. A piece of equipment so far outside the mainstream, I assert that any statement of code efficiency is arbitrary.

Appendix G also requires me to use a boiler efficiency from Ch 6, so on the other hand, I want to choose gas so I can get a code efficiency which is option C.
If I choose option C, the savings will be strongly dependent on the modeled price differential between coal/trash and natural gas. This is the savings projects really achieve and why they use coal/trash fired district plants.

The difference between these options may well be the maximum allowed differential of 4 EAc1 points.

I eagerly anticipate any other responses and the forthcoming DES Guide. (Did I miss the public comment period?)

Paul Riemer

Paul Riemer's picture
Joined: 2011-09-30
Reputation: 0

To make a long story short, I vote Option A except that a portion of your proposed fuel usage will be low-cost or free trash, and the baseline will use only coal, per "Exception to G2.4" in 90.1.

Read on at your own peril...

Paul, I agree with most of what you've said. In the definitions section of 90.1 they do include coal as a fossil fuel, so the intention of ASHRAE at least was to include coal among the fuel options.

I think you have an opportunity in the selection of the fuel source if the proposed plant is hybrid for coal and trash. If you did have a coal/trash-fired plant, then would you be treating the trash portion as on-site "renewable" fuel source in EAC1 and EAC2? (90.1 "Exception to G2.4") In that case you would run both models, but the trash would be free in the proposed design and the baseline would use coal alone as the standby source. That would be your gain in overall DES plant performance.

Coal plant efficiency-wise, I think you are left with using the documented efficiency of your actual plant that you suggest in Option A, but taking credit only for the cost of the trash. The default efficiencies presented in the DES memo don't seem to apply to baseline boilers, they rely on 90.1 for the baseline plant configuration. If your plants were instead hybrid with natural gas and trash, then you would use Chapter 6 for plant efficiencies.

You don't mention if you think the coal plant equipment in place would be more efficient than any other coal plant. If that isn't a point of emphasis, I would suggest taking the cost of trash and calling it a day.

Otherwise you'll need a CIR to have the USGBC approve a natural gas baseline boiler plant, but I'm not sure that the intent of the DES memo is to make a comparison against a typical boiler plant, or else the memo could have been simplified to say that. The USGBC seems to have gone out of the way to use fuel source as specified by 90.1 rather than compare against typical.

On the other hand, maybe they are just waiting for a CIR to come through to edit the guidance...90.1 does rely on Section 6.4 for baseline plant efficiencies, assuming that a DES would use the purchased heating method G1.1.1 which helped lead to this whole guidance memo in the first place...Good Luck!

David Eldridge, PE

David S Eldridge's picture
Joined: 2011-09-30
Reputation: 2000

I too would vote for Option A. I have a somewhat similar grey area

In a district cooling system with electric heating ASHRAE 90.1 prior to
the DES memo would have had the baseline be district cooling with
electric heating in step 1. The DES memo document irrespective of fuel
types available on site requires the baseline to be district cooling and
fossil fuel boiler in Step 1. ASHRAE 90.1 says baseline system must be
selected based on the heating source (and floor area and building type
etc) (See G3.1.1). There is a clear conflict here and I have not found
documentation on who supersedes what.

Minu Agarwal LEED AP

Minu Agarwal's picture
Joined: 2011-10-02
Reputation: 0

Minu, I think you should apply the DES memo only to the portions of the building that are served from the district cooling. So if your proposed building has on-site heating (electric or otherwise), then you are only using the DES memo for the cooling related systems.

Appendix G would apply as normal to your heating system in both proposed and baseline. Let me know if I'm not interpreting your question correctly.


David S Eldridge's picture
Joined: 2011-09-30
Reputation: 2000

If the building is registered before May 2008, can we just follow the APPG
for district cooling - i.e. use the chilled water and hot water costs for
the proposed building and chiller and boiler for the baseline. Is there any
DES memo for prior to May 28 registered buildings that I am missing?

Thanks in advance.


R B's picture
Joined: 2011-09-30
Reputation: 4

The Energy Information Administration flung an amazing little factoid
out there this week that went largely unnoticed: In April, for the first
time ever, natural gas-fired power plants put as much electricity on
the U.S. power grid as coal-fired power plants.


albert001's picture
Joined: 2012-07-13
Reputation: 0