Dear All, I am intending to model a building on campus which is connected to a campus energy system providing chilled water and hot water. As I would like to achieve more points and I know the properties of the district energy systems, I am opting for Option 2. I read the USGBC's guidance and modeled a virtual DES system for my proposed model. Now for the efficiencies, the guidance has conservative low values (heating efficiency of 70% and Cooling COP 4.4). I know that the installed DES boilers have an efficiency of 82% and the installed DES Chillers have a COP of 6.1. Can I simply use these efficiencies in my proposed model, or I have to account for the DES's part-load efficiencies? If so, then can I approximate the building's load to determine the corresponding efficiency from the part-load curves? The current DES is supplying 3 buildings, and my new project has 2 new buildings to be constructed, so can I roughly obtain the efficiencies at half load (or say at 40% of the full load)? Thanks!

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Tue, 12/31/2013 - 15:39

Yes you account for part-load efficiencies. The efficiencies are determined based on actual loading. The virtual plant is created to serve your project only not the entire connected load of the DES. See Appendix C in the DES v2 for detailed guidance.

Maya Karkour

EcoConsulting

LEEDuser Basic Member

549 thumbs up

Fri, 01/03/2014 - 16:29

Thanks Marcus. I'm modeling a school building. The DES was installed almost 8 months ago for the first phase of the project. Now, we are consulting for the second phase, and additional chillers / boilers will be added to the DES in order to be able to serve both phases in addition to any potential building on campus in the future. 1) Getting back to Appendix C, and in order to determine the proposed building heating / cooling efficiency, I'm assuming I cannot use the "Monitoring" option because the DES will be expanded as part of my project. Is this correct? 2) If yes, then I assume I have to go with the modeling option. For this option, do I have to create a separate model of the district plant, or shall I add this district plant to my project's model? Appendix C says "Apply measured or estimated load profiles as "process loads" to reflect the estimated total loads on the plant". If this is the case, then if I add the process loads in addition to my project's loads, I will be double counting the loads, right? Does this mean I have to create a dummy project building (with no loads) with the proposed district plant to determine the efficiencies? 3) Finally, is there additional guidance for modeling district energy systems, other than the one of the USGBC? Something with more examples or maybe a case study with actual numbers? Thanks!

Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Tue, 01/07/2014 - 19:26

1) Sounds right to me unless you want to wait until the DES is upgraded and then monitor. 2) You create a separate energy model. The process loads would represent all of the buildings on the DES. This model is just used for determining the plant efficiency. You then use this information is a separate model of your building as an input into the virtual plant within that model. 3) I am not aware of any additional guidance.

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