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

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For systems >300 tons where 2 chillers and therefore 2 primary chilled water and 2 condenser water pumps are present: do the 19 and 22 limits for condenser and chilled water pump energy apply to all pumps together? For example, would I take the W/gpm for the secondary chilled water pump and then add both the W/gpm for the two primary chilled water pumps to get to 22 total? Same for the condenser pumps, the sum of the W/gpm for both pumps should equal 19? This question has been answered numerous times before and the consensus has always been the sum of a single primary and single secondary should equal the limit, but I cannot find an instance where it was answered regarding multiple primary pumps.

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Joined: 2014-08-12
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Not quite, I think you are close though - try it this way: use the total plant GPM x W/gpm factor, and that gives your total watts to spread across any number of primary and secondary pumps (even if there was only one of each type). It is up to you to reasonably assign that power between multiple secondary and primary pumps.

As an example, if there are two equally-sized chillers and each has a dedicated primary pump, then each primary pump will have the same W/gpm for its half share of the flow.

If you assigned the secondary pump 15 W/gpm as an example, then 7 W/gpm would be left for each of the primary pumps, based on each pump's own gpm.

Total power and gpm are additive for pumps in parallel, but not W/gpm. W/gpm is additive for the total of the primary and total of the secondary, and should equal 22 W/gpm.

Likewise, assuming two dedicated condenser water pumps, each condenser water pump would have 19 W/gpm for its own share of the total gpm...gpm and total power will be additive, not W/gpm.

David

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates

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Joined: 2012-05-08
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Thanks, I think I got it. Take the loop flow from the PV-A report for chilled water and condenser water systems, multiply by 22 and 19 respectively, and make sure the sum of pump energies for all pumps on each system matches the allowable.

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Joined: 2014-08-12
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Here is the ASHRAE interpretation on this issue.

Hope this helps!

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Joined: 2011-04-11
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