[Equest-users] Baseline Chilled Water Loop

Paul Diglio paul.diglio at sbcglobal.net
Tue Nov 16 18:00:05 PST 2010


In 90.1 Section 3.2 Definitions, "Pump System Power: the sum of the nominal 
power demand of motors of all pumps that are required...."

This wording makes it clear that in a primary-secondary pumping system the sum 
should be 22W/gpm for both pumps, not per pump.

Paul Diglio





________________________________
From: "Bishop, Bill" <wbishop at pathfinder-ea.com>
To: John T. Forester <JohnTF at BVHis.com>; James Hansen <JHANSEN at ghtltd.com>
Cc: equest-users at lists.onebuilding.org
Sent: Tue, November 16, 2010 2:37:43 PM
Subject: Re: [Equest-users] Baseline Chilled Water Loop

 
I raised the question initially with John offline. My interpretation of “pump 
power shall be 22 W/gpm” is that each pump in a primary/secondary system should 
have this power. There is no wording that indicates that it should be otherwise, 
though I see Richard’s point that “gpm” could be interpreted to mean CHW 
produced. My chilled water system design experience is limited, so I don’t have 
a sense of “typical” CHW system pumping power. Using only the system that I am 
currently modeling for a project, the proposed primary pumps are 28 BHP and 953 
gpm, or 21.6 W/gpm for the primary loop. The secondary CHW pump uses a 20 HP 
pump at 380 gpm. I don’t have the BHP, but using 16 BHP results in 31 W/gpm for 
the secondary loop. So, my sample size of one already uses more pump power than 
a baseline system with 22 W/gpm applied to each of the primary and secondary 
pumps.
 
Bill
 
WilliamBishop , PE, BEMP, LEED® AP |Pathfinder Engineers & Architects LLP
Mechanical Engineer
 
 134 South Fitzhugh Street                 Rochester, NY  14608
T: (585) 325-6004 Ext. 114            F: (585) 325-6005
wbishop at pathfinder-ea.com           www.pathfinder-ea.com
P   Sustainability – the forest AND the trees.P  

________________________________
 
From:equest-users-bounces at lists.onebuilding.org 
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of John T. 
Forester
Sent: Tuesday, November 16, 2010 10:59 AM
To: 'James Hansen'
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Baseline Chilled Water Loop
 
James,
 
I see your argument that it is a challenge to design to 22 W/gpm.  However, 
using your example of 2,000 gpm and 22 W/gpm, are you suggesting that a 
44 kW (60-hp) motor is acceptable for a primary-only pump on a 1,000-ton 
chiller?
 
Section 11 states that the 22 W/gpm was chosen based on 75 ft of head and 65% 
combined pump/motor efficiency (the 90.1 User’s Guide actually says 60%) for a 
primary-only loop.  This would include all system pressure drops.  Again, this 
is not easy to design to.  But at least the Section 11 example is clear on how 
much pump energy to include in the baseline design.
 
John
 
John T. Forester, P.E., LEED AP, Mechanical Design Engineer I BVH Integrated 
Services I617.658.9008 tel I617.244.3753 fax IOne Gateway Center Suite 506, 
Newton MA 02458 I www.bvhis.com I Hartford ● New Haven ● Boston
From:James Hansen [mailto:JHANSEN at ghtltd.com] 
Sent: Tuesday, November 16, 2010 10:23 AM
To: Richard Ellison; John T. Forester; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Baseline Chilled Water Loop
 
As I indicated earlier, everyone has their own opinion about this credit.  But 
consider this:
 
The pressure drop across a cooling tower and condenser water piping system is 
roughly the same as the pressure drop thru the chiller evaporator and primary 
loop of a primary/secondary chilled water plant (on a per gpm basis once you 
correct for the higher flow rates of the condenser side).  In other words, on a 
PER GPM basis, a typical water-cooled chilled water plant will have similar pump 
HP per GPM for the condenser water system and primary chilled water system.  Not 
identical, but similar.  I’ve got 10+ recent base-building designs that confirm 
this.  90.1 requires 19 W / gpm for a condenser water system, and you are saying 
that you only model 6 W / gpm for the primary chilled water pump?  That is below 
realistic design values for a primary system, at least in my opinion.  

 
Example:  1,000 ton chiller at 54/42 requiring 2,000 GPM.  6 W / gpm thru the 
primary loop would only use 12.0 KW, or a 15 hp motor frame.  If you assume a 
chiller evaporator loss of 15 ft, and make only modest estimates of an 
additional 20 ft for piping losses, strainers, mixing valves, bypass valves, etc 
(35 ft total), you can try and select any pump you want but you’re going to need 
at least a 25 hp motor.  And with most chilled water plants, even 35 ft seems 
low for the pressure drop across a primary loop.  I don’t see how 6 W / gpm can 
accurately represent a chilled water primary loop even in the most efficient 
central plant designs.  

 
Furthermore, if ASHRAE had wanted us to prorate the 22 W / gpm between the 
primary and secondary loops, wouldn’t they have instructed us to do that, 
especially since there is a huge difference in energy consumption depending on 
which of the two loops has the higher W / gpm?  Have they instructed us to do 
that in an addendum?
 
I stand by my use of 22 W / gpm for each pump, and have never had a reviewer 
instruct me to do otherwise (which of course doesn’t mean that I’m not wrong).  

 
GHT Limited
James  Hansen, PE, LEED AP
Senior Associate
1010 N. Glebe Rd, Suite 200
Arlington,  VA   22201-4749
703-338-5754 (Cell)
703-243-1200 (Office)
703-276-1376 (Fax)
www.ghtltd.com
 
 
From:Richard Ellison [mailto:REllison at southlandind.com] 
Sent: Tuesday, November 16, 2010 9:27 AM
To: James Hansen; John T. Forester; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Baseline Chilled Water Loop
 
I usually don’t respond to the information on this forum but I completely 
disagree with this latest e-mail.
 
The chilled water is supplied by a chiller not a pump.  “The baseline design 
pump power shall be 22 W / gpm” is for the GPM delivered by the chiller and the 
pumping system does not matter. The power is specified per GPM not per pump.  
 If you use primary/secondary then the energy is divided between the pumps.  We 
usually assume 6W/gpm for the primary pump and 16W/gpm for the secondary pump.  
If one uses 22W/gpm for each pump, then the total of 44W/gpm the pump energy is 
huge and the savings unrealistic.
 
R I C H A R D  E L L I S O N
PE, CEM, CEA, CTAB, CBEP, LEED AP 
Energy Engineer
Southland Industries
22340 Dresden Street, Suite 177
Dulles, VA 20166
Office: 703.834.5570
Direct: 703.834.2438
Fax: 703.834.5572
 
From:equest-users-bounces at lists.onebuilding.org 
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of James Hansen
Sent: Tuesday, November 16, 2010 8:50 AM
To: John T. Forester; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Baseline Chilled Water Loop
 
I’ve seen different people provide different responses to this question, but 
I’ve always modeled EACH pump in a chilled water system as 22 W / gpm.  Don’t 
prorate.
 
“The baseline design pump power shall be 22 W / gpm”.  It can’t be any more 
clear than this.  90.1 tells you when you need a primary / secondary system, and 
when you can get away with primary only.  In other words, they are telling you 
how many pumps you need to model.  And they specifically list the pump power in 
terms of GPM, which is PER PUMP.  Nowhere does it say to prorate.
 
GHT Limited
James Hansen, PE, LEED AP
Senior Associate
1010 N. Glebe Rd, Suite 200
Arlington, VA  22201-4749
703-338-5754 (Cell)
703-243-1200 (Office)
703-276-1376 (Fax)
www.ghtltd.com
 
 
From:equest-users-bounces at lists.onebuilding.org 
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of John T. 
Forester
Sent: Tuesday, November 16, 2010 8:41 AM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Baseline Chilled Water Loop
 
Fellow Modelers,
 
I’ve received a comment regarding my response last week on how to model CHW 
pumps for App. G.  Specifically, item 7 (see below) 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)
“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.”
 
The question: 
Should each primary and secondary pump be sized for 22 W/gpm OR should this 
“design pump power” be divided up (in some way) between the primary and 
secondary pumps?
 
Position 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.  This would maximize the pump energy in the baseline model.
 
Position 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.  The “design pump power” of 22 W/gpm is the same requirement as Section 11 
(ECB method) just with a different pumping configuration.
 
How do you interpret (and model) 90.1 App. G chilled-water pump power 
requirement of 22 W/gpm?  (Your interpretation doesn’t necessarily have to be 
one of the positions above.)
 
Thanks,
 
John
 
 
John T. Forester, P.E., LEED AP, Mechanical Design Engineer I BVH Integrated 
Services I617.658.9008 tel I617.244.3753 fax IOne Gateway Center Suite 506, 
Newton MA 02458 I www.bvhis.com I Hartford ● New Haven ● Boston
From:equest-users-bounces at lists.onebuilding.org 
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of John T. 
Forester
Sent: Friday, November 12, 2010 5:47 PM
To: 'Smith, Michael'
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Baseline Chilled Water Loop
 
Hi Michael,
 
I think I can answer your App G question.
 
First, in the context of 90.1, “variable flow” does not necessarily mean 
variable speed.  It just means riding the pump curve with a bypass to minimize 
pumping pressure drops through the loop during part-load operation.
 
App. G Chilled Water Modeling <=300 tons
1.       Create a chilled water circulation loop and name it something like “Pri 
CHW Loop.”
2.       Create another chilled water circulation loop and name it something 
like “Sec CHW Loop.”
a.      Change the Loop Sub-type of this loop to Secondary and choose “Pri CHW 
Loop” as the primary loop.
3.       Create a circulation pump and name it something like “Sec CHW Pump.”
a.      Set this pump as variable speed.  I believe you are allowed to set the 
minimum speed to 50% for App. G. (someone here on the list can correct me on 
this if I’m wrong).
b.      By default, the valve on this loop is three-way and will circulate water 
directly back to the primary loop as long as there are two-way valves at your 
terminal units (AHU coils, FCUs, etc).
c.      Attach this pump to the Sec CHW Loop.
d.      Change the loop head sensor location to “at coils.”
4.       Create a condenser water loop and CW pump and attach the pump to the 
loop.
a.      Also create an open tower heat rejection device and attach it to your 
condenser water loop.
5.       Create 1 primary chilled water pump per chiller.  They won’t be 
attached to anything yet and will be at the bottom of the component tree.
a.      The default for a pump is “One-Speed.”  This is fine and the pump will 
act as a constant volume pump with the three-way valve on the secondary loop.
6.       Create a water-cooled chiller and choose the “Pri CHW Loop 1” and 
“water-cooled.”
a.      Since there is no pump attached to the primary loop, you will be 
required to select a pump for the chiller.
b.      You will also be required to select the Condenser water loop
7.       Now what you have to do is size your pumps so the total pump energy is 
22 W/pm.  You will want to do something like 4-5 W/gpm for each primary pump and 
use the remaining for the secondary pump.
 
This system is primary/secondary with constant flow through each chiller and 
variable speed/variable flow through the secondary loop.  Since each chiller has 
a pump directly attached to it, each primary pump will automatically cycle on 
and off with the chillers.
 
 
 
John T. Forester, P.E., LEED AP, Mechanical Design Engineer I BVH Integrated 
Services I617.658.9008 tel I617.244.3753 fax IOne Gateway Center Suite 506, 
Newton MA 02458 I www.bvhis.com I Hartford ● New Haven ● Boston
From:equest-users-bounces at lists.onebuilding.org 
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Smith, Michael
Sent: Friday, November 12, 2010 3:55 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Baseline Chilled Water Loop
 
Everyone,
 
I have a question regarding the baseline chilled water loop. 
 
ASHRAE 90.1 2007 Section G3.1.3.10 states that for large chilled water systems 
serving baseline systems 7 and 8 that are greater than 300 tons the loop “shall 
be modeled as primary/secondary with variable speed drives on the secondary 
pumping loop.”
 
The following section, G3.1.3.11 further goes on to say that “each chiller shall 
be modeled with separate…chilled water pumps interlocked to operate with the 
associated chiller.”
As clarification, does this mean three sets of pumps are required, or just two? 
Are the “primary” loop pumps specified as the chiller pumps? 

Two reasons why I am confused. Firstly, the Chapter 11 baseline chilled water 
loop is supposed to be simulated as primary-only variable flow, but still has 
the similar requirement for interlocked chiller pumps. That would be two sets of 
pumps. Adding a “secondary” loop actually adds a third set of pumps. 

The second reason why I am confused is that the Simulation Guidebook prepared 
for Pacific Gas and Electric (same affiliation as CoolTools) has a visual of how 
to simulate “primary/secondary” loops on page 52, but they do not include 
chiller pumps in their image of the eQUEST component tree. 

I can’t understand why three sets of pumps would be required. I supposed a 
follow up question may be if the 22 watts/gpm is inclusive of all three sets of 
pumps. Hopefully someone can clarify! I appreciate your help. 

 
 
Michael J. Smith, EIT, LEED® AP
WSP▪FLACK + KURTZ
512 7th Ave., New York, NY 10018
Direct: 212.951.2671| Main: 212.532.9600
www.wspfk.com
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