We are wondering how to interpret the Minimum Efficiency Tables of Chapter 6.8 in ASHRAE 90.1-2007 to model HVAC efficiencies of baseline equipment.
Our baseline building has a floor area > 150.000 ft² so we selected a chilled water system and a cooling load greater than 300 tons so we selected two equally sized water cooled screw chillers. For 320 tons the chillers are sized 160 tons each.
What should be the COP of this two chillers according to Table 6.8.1C?
Should it be 5.55 according to the equipments size or should it be 6.10 according to the cooling load of the building?
In general what is the meaning of size category in this tables, the building load or the equipment size.
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Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
March 11, 2011 - 11:55 am
You select the chiller type based on building cooling load using Table G3.1.3.7 as you have done. Assuming that 320 tons is your peak load in the baseline you take that size, divided by two screw chillers, and apply it in Table 6.8.1c. According to that table, for screw chillers in that size range the COP is 4.9. Looks like you may have been looking at the efficiencies for centrifugal chillers.
Good news is that your savings hould increase!
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
March 11, 2011 - 11:57 am
Oh yea - short answer is that you use equipment size in Table 6.8.1c, not building load.