My project is an addition to an existing facility, so the CHW and HHW comes from a district plant. I am modeling the plant as cost neutral, purchased CHW and HHW in baseline and proposed. My proposed design has 2 ORs that are designed to a 55F setpoint using an air-cool glycol sub-cooling chiller that is dedicated to this addition. I am using G3.1.1 exception b to put those two ORs on their own system 3s. Should I make the cooling source for the system 3s DX or put them on the purchased CHW loop? Technically the purchased CHW loop doesn't make cold enough water to sub-cool the OR to 55F, and their cooling source is not part of the district loop (the first stage is in reality).
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Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
June 13, 2018 - 1:29 pm
The DES guidance for v4 refers you to Appendix G. Sections G3.1.1.1, G3.1.1.2, and G3.1.1.3 indicate it should be the CHW loop and the system 3 should be treated as an AHU. That said I think that you could consider the sub-cooling chiller to be a process load and therefore modeled identically in both models. Might be able to claim some efficiency gain through an exceptional calculation.