App G Baseline CHW Pump Power

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Hello,

In November 2010, around the same time someone was modeling a building that looked like a turkey, there was a conversation on this list about baseline CHW pump power:

http://lists.onebuilding.org/htdig.cgi/equest-users-onebuilding.org/2010-November/006941.html

Part of the discussion was some back and forth about how to apply G 3.1.3.10. This section calls for baseline pump power to equal 22W/GPM and for the CHW pumping configuration to be primary/secondary. Some had the opinion that each pump (primary and secondary loops) should have 22 W/GPM assigned to it, while others thought that the total CHW pump system power should sum to 22 W/GPM, and that it was up to the modeler to divvy up the power among pumps as they see fit. I did not see a clear conclusion.

Does anyone know if a general consensus was reached?

Thanks,

Christian Kaltreider, LEED AP 

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Almost certain that the GBCI interprets it as a whole system divvy, not each pump with 22W/GPM.

Regards

Joe Fleming | PE, LEED AP BD+C, BEMP

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Christian,

Confirming what Joe says, an ASHRAE interpretation clarified that 22W/gpm is the total power of all baseline CHW pumps.

Regards,
Bill

William Bishop, PE, BEMP, BEAP, LEED AP

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Yes, that lays it out pretty clearly. 22 W/GPM system total.

I wonder if future 90.1 versions will prevent gaming of the system (intentional or not) by offering guidance on power allocation among pumps?

Thanks for the helpful replies,

Christian

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Joined: 2011-09-30
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Thanks for bringing that back up - I thought this remained an ambiguous/grey area indefinitely.

As to potential for squeezing extra performance via power distribution between pumps? I?ve never considered that, but to share my anecdotal experience I typically just dump all the power on the secondary pumps and make the primary pumps ?powerless? for simplicity?s sake in documentation/QC. I suppose for variable-secondary cases that approach might miss out on some baseline energy that would otherwise be burned by a CV primary?

A ?logical? approach would be to proportion the ?system? 22W/GPM by a ratio to match the pump sizing in the actual design.

That said, I?ve never been told to proportion my pump energies any differently than my simplified approach of dumping it all in one place.

Hope that helps =),

~Nick

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For what it's worth, I've used 22 W / gpm for each system (primary and secondary) for the past few LEED projects, and have not had any comments, given that the LEED "Revised Section 1 4 Table" from Dec 2012 specifically lists that the primary and secondary pumping system should be at 22 W / gpm. By the way, if you're not using the Table 1.4 excel spreadsheet to document EAp2/EAc1, you should, because it makes it way easier for GBCI to review your model, and it minimizes the chance and/or severity of comments.

CHW Loop Configuration

Primary/secondary per G3.1.3.10

N/A

N/A

Number of Primary CHW Pumps

1 per chiller per G3.1.3.11

N/A

#

N/A

#

Primary CHW Pump Power

22 W/gpm per G3.1.3.10

N/A

N/A

W/gpm

Primary CHW Pump Flow

Auto-sized with a capacity ratio of 1.0 based on CHW temperatures

N/A

gpm

N/A

gpm

Primary CHW Pump Control

Constant Flow - each primary pump interlocked to operate with associated chiller - G3.1.3.10, G3.1.3.11

N/A

N/A

Number of Secondary CHW Pumps

1 per G3.1.3.10

N/A

#

N/A

#

Secondary CHW Pump Power

22 W/gpm per G3.1.3.10

N/A

W/gpm

N/A

W/gpm

Secondary CHW Pump Flow

Auto-sized with a capacity ratio of 1.0 based on CHW temperatures

N/A

gpm

N/A

gpm

Secondary CHW Pump Control

<300 tons: riding the pump curve

?300 tons: variable speed

N/A

N/A

Regardless of how ASHRAE has ruled, GBCI makes it pretty clear that you should use 22 W / gpm for both primary and secondary loop pumps.

GHT Limited

James Hansen, PE, LEED AP, BEMP

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Oh wow, good to know! I?ll re-revise the procedure I?ve written up for my next chiller baseline!

Thanks to GBCI for internally ruling this in a way to grant extra performance/points, I suppose!

~Nick

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James,

The ASHRAE interpretation came around or after the latest Table 1.4 template was released, both in December 2012. I think that it is fair to assume that the USGBC just missed the point on this one and despite that any good reviewer should push back on using 22 w/gpm on both pumps. The template supplied by the USGBC is a tool to document the model inputs and not what is used to stipulate how to model and follow the PRM.

The PRM is the only set of rules to which EAp2/EAc1 performance is developed with the only official deviation from what is contained within it is the DES guidance produced by the USGBC.

Gaming the performance of a model because of this misinterpretation by the USGBC is bad for the modeling community and should be avoided.

Tim.

Timothy Howe, MS, BEMP, LEED? AP

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Nobody is gaming the system Tim. I'm working on a couple LEED v4 pilot projects, and the spreadsheet for the Minimum Energy Performance credits still lists 22 W / gpm for both systems (and it is a REVISED spreadsheet in a totally different format, not something that was copy/pasted from the v3 spreadsheet).

I can send it to you offline if you don't have access to the new templates.

For reference, my last primary / secondary chilled water job had a condenser water pump needing 50 feet of head, a primary chilled water pump needing 58 feet of head, and a secondary chilled water pump needing 65 feet of head. This would fall exactly in line with the 19 W / gpm allowance for condenser water, and 22 W / gpm for each of the chilled water pumps. Perhaps GBCI had an internal ruling based on the hundreds of chilled water plant projects they see each year??

GHT Limited

James Hansen, PE, LEED AP, BEMP

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Has had comments. ? Must depend on reviewer. ? Be careful you don't put to many eggs into that basket.

Joe Fleming, PE, BEMP, LEED BD&C

-------- Original message --------

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All:

I don?t expect Timothy meant to be accusatory, but rather primarily to suggest we as a modeling community have a responsibility to hold true to the ?intent? of such standards.

I think this is true, but in my humble opinion, the 22W/GPM figure itself is frankly arbitrary at best when considered against various actual designs, and the critical thing from a ?LEED fairness? perspective is for this to be applied consistently project-to-project.

To that point, and specifically for the context of LEED, I feel the onus is on GBCI and not the individual modelers to define and apply such rules consistently. They?ve proven quite capable of updating their EAp2 spreadsheet often (and I wouldn?t be surprised if we saw a change for future projects in response to this thread).

As to what?s right/wrong here, the modeler?s interest for a given project is to be concerned first for their design team?s goals of ?earning? as many points as 90.1 and GBCI?s rulings legitimately allow for. I think for a LEED project, any written direction from GBCI takes precedence over Appendix G.

That said, for a LEED project and pending any additional clarification from GBCI, I think it?s totally appropriate to apply whatever interpretation you think is correct, and either approach described is defensible for different reasons.

Outside the context of a LEED/90.1 model, you?re probably better off assigning baseline pump energies to match actual pump design as exists or as would be provided anyway, if you?re trying to demonstrate savings with better control strategies or configurations.

Best regards,

~Nick

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I would second what Tim is saying. The ASHRAE interpretation is much more of an official final take than a line in a spreadsheet that does not have the correct caveat attached to it. I?ve always found it tricky to figure out how to apply the 22 W/gpm when you have a constant primary / variable secondary system. Maybe a better way to look at it is that the pumps should be set at 75 ft of head and 60% combined motor/mechanical efficiency. Which is equivalent to 22 W/gpm if you go through and do the conversions. Also see the 2007 user manual page G-31.

Brendan Hall, PE, LEED AP BD+C

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Strike that, you would still need to split up the head between the two pumps. But it makes it a bit easier to conceptualize if you think of it as pump head as opposed to W/gpm.

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