[Equest-users] CHW Loop and Chiller Sizing

Holt Cutler HCutler at EMEGroup.com
Tue Oct 25 08:35:54 PDT 2011

Equest Users,

I'm working on the plant system in my model now, and having some trouble getting the chiller and the CHW loop to size appropriately in equest. The chilling configuration for the project includes a primary and secondary loop and two chillers operating in parallel. The primary loop serves chilled water to several AHUs, and the secondary provides chilled water to Fan Coil units at the zones. With 'Loop Size Ratio' set to 1.0, and 'Sizing Option' set to Secondary for the primary chilled water loop, I expect to see the cooling capacity match the peak coil load as indicated in the PS-H report. However, my primary CHW loop is sized to a cooling capacity of 7,315 KTBU/hr while the peak load is 3,980 KTBU/hr. As a result, the average chiller part load, also in PS-H, hovers around 12% and rises above 50% for only 3 hours of the year. This part-load operation seems unreasonable.

What is effecting the CHW loop sizing other than the peak coil load reported in PS-H, the 'Loop Size Ratio,' and 'Sizing Option' specified for the loop? One thought that I had was that selecting Non-Coincident vs Coincident as the AHU 'Sizing Option' will effect the size of the CHW loop, however, this effect is captured by a rise in the peak coil load. Any suggestions would be appreciated.


Holt Cutler, LEED AP

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