Hello,
I'm confused on how to interpret CHW pumps for App. G. Specifically, item 7 and 8 and how the 22 W/gpm is defined for a primary secondary configuration. Section G3.1.3.10 can be interpreted (at least) two different ways.
First, Section G3.1.3.10 Chilled-Water Pumps (Systems 7 and 8)
â??The baseline design pump power shall be 22 W/gpm. Chilled-water systems with a cooling capacity of 300 tons or more shall be modeled as primary/secondary systems with variable-speed drives on the secondary pumping loop. Chilled-water pumps in systems serving less than 300 tons cooling capacity shall be modeled as primary/secondary systems with secondary pump riding the pump curve.â??
The question:
Should each primary and secondary pump be sized for 22 W/gpm OR should this â??design pump powerâ?? be divided up (in some way) between the primary and secondary pumps?
Possibility A:
If the 22 W/gpm should be the TOTAL pumping power, there is no guidance on how to divvy up this requirement and the constant volume primary pumps could be sized for 20 W/gpm and the secondary (VSD or riding pump curve) can be allotted 2 W/gpm.
Possibility B:
Sizing each primary pump and secondary pump to 22 W/gpm will over-estimate the baseline pump energy (VSD or riding pump curve) and this is not the intent of 90.1.
How do you interpret (and model) 90.1 App. G chilled-water pump power requirement of 22 W/gpm?
p.s. I'm clear on what parameters needs to be changed in order to get 22W/GPM but i'm curious in knowing the modeling approach. Should i consider it as Complete system approach OR individual loop/pump approach?
Thanks,
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Javed Iqbal, LEED AP, CEA
Energy Analyst
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