[Bldg-sim] Appendix G Secondary Pump Control

[Bishop, Bill]

Christian,
I always model one secondary pump for the baseline. I see no reason to do otherwise.
My approach to loop activation has been to model it the same as the proposed design. Using DOE-2 for example, it could be SCHEDULED to run 24/7 during cooling months, or DEMAND-ONLY to stay off until a coil or process load exists. If the proposed design has no CHW plant, but has a boiler/HHW plant, you could model the baseline CHW loop activation similarly to the proposed HHW loop. If the proposed design has no analogous loop operation, you just have to make a judgement call, but I am not aware of any guidance in 90.1 or LEED. Also keep in mind that 22W/gpm is the total pump power allowance for all your primary/secondary CHW pumps, and not the power of each pump.
Regards,
Bill

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

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From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Christian Kaltreider
Sent: Friday, December 20, 2013 9:15 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Appendix G Secondary Pump Control

I have a question regarding 90.1 2004 Appendix G baseline chilled water pump control.  Section 3.1.3.10 says that baseline CHW systems must be primary/secondary, with a constant flow primary loop and a variable flow secondary loop.  The secondary pump will either ride the curve or be controlled by a VSD depending on square footage.  In the case I currently have in my hands, the pump rides the curve.  No questions yet.

Section 3.1.3.11 goes on to state that each chiller shall have its own condenser water and chilled water pumps, interlocked to operate with the chiller.  This is clear and reasonable for the condenser water and primary chilled water pumps, but what about secondary chilled water pumps?  For my current application (one chiller, pump riding curve), my question simply boils down to whether I should turn the secondary pump off when the chiller is off, or if I should run it all of the time.

But to get into it a little more, here are three approaches I see:


1.       Model one secondary pump for each chiller, and turn each pump off when its associated chiller turns off.  Section 3.1.3.10 is titled Chilled Water Pumps, and that section includes both primary and secondary pumps, so when the next section references "chilled water pumps" that should include both primary and secondary.  However, this does not reflect the typical reality of one secondary pump serving multiple chillers, and the common interpretation that only a primary pump has one single associated chiller.



2.       Model one secondary pump regardless of how many chillers there are, and turn it off when all chillers are off.  This is perhaps most similar to what you might expect in a 'real' system.  If you only have one chiller (as I currently have), this is exactly the same as approach 1.


3.       Model one secondary pump regardless of how many chillers there are, and never turn it off.  Many buildings are unfortunately operated this way.  This approach significantly increases baseline energy when the pump is riding the curve.

I have always used approach 2 without putting much thought into it.  But now my results are highly dependent on which approach I take, and I see enough ambiguity that arguments could be made for approach 3.

Your thoughts?

Thanks,
Christian


Christian Kaltreider, LEED AP | Energy Analyst
Sud Associates, P.A. | T 828.255.4691 | F 828.255.4949 | www.sudassociates.com<http://www.sudassociates.com>


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