District Heating and District Cooling

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All,

I am trying to model a building that will have chilled water and hot water supplied by a Central Utility Plant. According to the attached "Required Treatment of District Thermal Energy in LEED-NC version 2.2 (May 28,2008)", there will be 4 models required. The first set of 2 with purchased CHW and HW. The second set of 2 with the entire CUP modeled in the Proposed case and a boiler/chiller plant autosized for the Baseline case.

If that reasoning is correct, then how do I account for the energy used by the other buildings using the CUP? Do I add it on as Process Energy on my Chilled Water and Hot Water loops? How do I calculate the load on the Condenser Water loop? What if I don't know what the loads in the other buildings are?

Thank you in advance!

Linda Lam, LEED?? AP

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Linda,

Page 7 of the LEED document instructs you to "use a virtual heating plant with the same seasonal heating efficiency of the entire upstream DES heating system" and goes on to say that it is permissible to model part load conditions. There is similar wording for the CHW plant. You don't need to use the actual capacities of the plants or the attached loads, just the actual efficiencies (and an estimate of the part load curve possibly). Which is much simpler than trying to account for everything else attached to the plant.

Matt Dubrovich, P.E.

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Thanks Matt,

I was confused by the line right after the lines you quoted for me, on page 7: "The DES central plant itself shall always be modeled as a total, entire unit."

Unfortunately I don't think we have a part load curve for the CUP yet. Do you have a sense of how off my energy use will be? I'm guessing the default PL curve for Electric Centrifugal Chiller is on the conservative side...

Best,

Linda Lam, LEED?? AP

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