How to model the 90.1-2010 Appendix G Baseline for a building with an onsite water-cooled chiller using a DES for heat rejection?

asked 2021-09-22 09:48:53 -0600

umop-3pisdn gravatar image

updated 2021-09-22 11:34:15 -0600

Using DesignBuilder v7 to create a 90.1-2010 Appendix G model of a 3-floor, 96,000 SF archival facility on a college campus. Dehumidification in the archival spaces 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. Cooling for the non-archival spaces is provided directly by the campus chilled water system. Since the proposed case uses purchased chilled water for cooling (even though it uses electricity for this as well), I interpret 90.1-2010 Section 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.

  1. Does this approach seem correct?
  2. 90.1-2010 Sections 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 the above approach is correct, could the baseline CHW DES serving the archival space systems be modeled identically to the proposed (i.e. 35F SWT, no reset), with another CHW DES at the G3.1.3.8 and G3.1.3.9 temps serving the non-archival space systems?
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