Working on a model of a 3-floor, 96,000 SF archival facility on a campus. Dehumidification is very important and provided by low-dewpoint supply air. The air is cooled by 35F chilled water/glycol generated by an onsite water-cooled chiller, which has its condenser side connected to the 45F campus chilled water system. "Cooling" is the chiller compressor energy, "heat rejection" is the energy transfered via the campus chilled water heat exchanger. Since the proposed case uses purchased chilled water for cooling (even though it uses electricity for this as well), I interpret G3.1.1.2 to indicate that the proposed should be modeled as designed, but the baseline should be modeled with System 7 + System 3 (with CHW coil, not DX) served by purchased chilled water only with NO chiller.
Questions:
- Does this approach seem correct?
- G3.1.3.8 and G3.1.3.9 define the baseline CHW temps as 44F SWT &12F Delta-T with OAT reset, which won't allow the required dehumidification. Assuming this approach is correct, could the baseline CHW DES be modeled identically to the proposed (i.e. 35F SWT, no reset)?
Thanks in advance!
Tyler Thumma
7GroupLEEDuser Expert
60 thumbs up
December 15, 2021 - 3:33 pm
1. Yes, this seems correct.
2. I don't think this approach would be permitted outside of an exceptional calculation which would need to be approved on a case-by-case basis. If the Baseline system as fully defined in Appendix G is not capable of maintaining required space humidity setpoints, then it may need to be considered as a process application and all system parameters modeled identically to the Proposed design. Any efficiency measures would again be modeled as an exceptional calculation.