What is the best strategy/software to model District Cooling for LEED

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Mar 31 2011 Guest
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This has been a challenge for me on several projects. If I am designing a large district energy plant and an associated building, which will only consume a small amount of the plant's output, how do I properly capture the efficiency of the plant? USGBC guidance seems to leave this fairly open, but I would like to hear what others have done in the past. I typically use TRACE for energy modeling, and have been told that TRACE does not have this capabilty.

Any insight would be appreciated.

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W. Edward Locke, CSI-CIAQP-M.SAME President The Design Group, Inc.
Jan 27 2013
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Best energy modeling software

Receiving conflicting reports about best most accurate energy modeling software. Some say Trane Trace while others comment about Carrier HAP; especially since HAP-4.61 will now permit VFR type equipment. Several professionals use EQuest, most likely because the software is free.

Would really like to know which is better for our client and approval success on first time submittal through LEED on-line.

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Susan Walter Sr Project Architect, Wilmot/Sanz Jan 29 2013 LEEDuser Expert 13737 Thumbs Up

We're architects and struggle with a similar question. Is there a better energy modelling software for different stages of design? The Trane Trace and Carrier HAP programs require loads to be inputted when these may not be understood at schematic design. ( I don't want to deal with unmet hours at that level for example.) Our struggle with equest is the assumptions on the energy side and it is not exportable to Trace or HAP. What are people using in the early stages for energy modelling? Are these impacted by BIM? Any recommendations for Revit plug ins or additional software?

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Adele Bluck
Jul 21 2011
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CHP modelling Option 1 question

We are trying to account for a CHPCombined heat and power (CHP), or cogeneration, generates both electrical power and thermal energy from a single fuel source. plant near our project in our energy model. The owners of the plant are very secretive and treat efficiency data as a trade secret, so it appears that we would have to go for the Building stand-alone scenario in the USGBC's DES Guidance (i.e. Option 1).

Looking through the methodology, we would have to model the non-DES parts of the system as per ASHRAE App G. However, according to the guidance, the parts of the building supplied by the DES would have to use a "virtual DES rate", which is derived from the virtual energy rate by multiplying the fuel and electric rates by a weighting factor. I assume that the weighting factor reflects some sort of average CHP efficiency, though the guidance does not explain it any further where those weightings numbers come from.

So far I can make sense out of this, but the last sentence of the guidance for Option 1 states that the same virtual DES-rates should be used as inputs for both the Baseline and Proposed buildings, which is where it gets very confusing. If we use the same rates for both Baseline and Proposed cases, aren't we just modelling the same building as if it didn't have any CHP at all? It appears to be that this approach eliminates any efficiency improvements arising from the use of the CHP plant and we would just be modelling as we would have done without any CHP.

Could anyone help me shed some light on this? Thanks for any help in advance.

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Justin Grissom
Apr 01 2011
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Update

And yes, I am familiar with the USGBC district heating/cooling guidance. This question is geared mostly to the energy modelers out there.

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Julian Bott Principal Design Consultant, Cundall Hong Kong Apr 04 2011 LEEDuser Member 813 Thumbs Up

Justin

My experience is on cooling side only, we have little use for heating on the DCS we have modelled.

It would depend if you particular target in mind for the small building and/or are you planning on using the DCS to justify its good energy performance?

I would suggest targeting efficent features in the small building (required anyway to prove it complies with ASHRAE)

Then I would recommend considering using the default COP of 4.4 for the whole DCS plant as a starting point.

If you do a really detailed model and have very efficent plant you can have a higher COP by around another 10-15% . If that makes a big difference to your overall strategy then look at it in more detail.

But from experience I would stick with the defaults in concept stage and for LEED points evaluation.
Only model in detail to develop up the detailed plant selections and control strategies to justify upgrading the DCS plant if you need to justify further changes to improve its efficency.

As for software we use TAS or IES for the buldiling and cooling loads. For the DCS simulation we use a very complex computer program otherwise known as excel with 8760 rows and hourly calculations.

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