# Pump Power Limit (19W/gpm & 22 W/gpm)

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So, does the ASHRAE interpretation IC 90.1-2007-14 imply that the "gpm" used in the calculation should be only the flow rate of the primary loop (or alternatively, only the secondary loop)? For example, if you have a CHW system with 500 gpm flow in the primary loop and 500 gpm flow in the secondary loop (they are only equal if the loop delta-t is equal), is the "gpm" in "22W/gpm" 500 gpm or 1000 gpm? I have not seen this explicitly defined anywhere.

Thanks,
Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

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Based on everything I have read through various sites and opinions it to take the loop flow from the PV-A report for condenser water and chilled water and use that as the basis for the flow. Multiply that flow by the W/GPM to get the maximum allowed. Then make sure that the sum of the power (KW) for all pumps under the PUMP section on that system do not exceed that maximum.

So in your case, you would use 500 GPM to determine the maximum. Thinking about it logically that would make sense. If you have a variable primary pumping system rather than a primary/secondary the total head for the variable primary at 500 GPM should be close to the split head of 500 GPM through the primary and the secondary loops separately.

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