[Equest-users] Baseline Chilled Water Loop
Paul Diglio
paul.diglio at sbcglobal.net
Fri Nov 19 10:24:55 PST 2010
FYI, I called the engineer at ASHRAE and he is researching this question and
promised to respond.
I will forward his response as soon as I receive it.
Paul Diglio
________________________________
From: Paul Riemer <Paul.Riemer at dunhameng.com>
To: "Bishop, Bill" <wbishop at pathfinder-ea.com>; Paul Diglio
<paul.diglio at sbcglobal.net>; John T. Forester <JohnTF at BVHis.com>; James Hansen
<JHANSEN at ghtltd.com>
Cc: "equest-users at lists.onebuilding.org" <equest-users at lists.onebuilding.org>
Sent: Fri, November 19, 2010 1:07:01 PM
Subject: RE: [Equest-users] Baseline Chilled Water Loop
If you argue that you can apply the 22 W/gpm to the secondary as a standalone
loop power, then you are either arguing 1) the primary gets the same 22 W/gpm or
2) the primary is not addressed.
Both of those seem pretty unworkable.
So, I still think the 22 W/gpm is a system value not a per loop value and the
missing direction is in the break out between the primary and secondary. If you
have a primary/secondary system, I would state your case for keeping the primary
power the same in both models. If your design does not have primary/secondary
or chilled water at all, then you will have to use your judgment.
You do not have to design to 22 w/gpm, you are just compared against it under
Appendix G. I am not saying that agree that the value of 22 W/gpm is the right
reference for all building types, shapes, sizes, and locations but the intent is
mostly clear.
Paul Riemer, PE, LEED AP
Associate / Mechanical
Direct: 612-465-7696
DUNHAM
Celebrating 50 Years of Service
From:equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop, Bill
Sent: Wednesday, November 17, 2010 9:04 AM
To: Paul Diglio; John T. Forester; James Hansen
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Baseline Chilled Water Loop
Paul,
Thanks for adding to the conversation. John and I were hoping more people would
contribute. Like James, I think the wording is ambiguous enough that
clarification is required from ASHRAE. I’ll add a few more comments.
· If Appendix G. used the wording “pump system power”, rather than “pump
power”, I would agree that 22 W/gpm should be the sum of the power of all pumps
in a system.
· Richard Ellison commented that this should be compared to the Appendix
G fan power calculation, which describes the method to calculate total fan
system power, not power for each fan in the system. However, the heading for
90.1-2007, G3.1.2.9 is “System Fan Power”, whereas G3.1.3.10 is “Chilled-Water
Pumps (Systems 7 and 8)”. Again, the wording “pump system” is not used in
Appendix G. The heading “System Fan Power” was changed from the 90.1-2004
wording of “Supply Fan Power”, making it less ambiguous.
· CHW systems are only modeled for the baseline for buildings with 6 or
more floors, or >150,000 ft^2, so we are not modeling small systems which would
have less head loss. In Section 11, where the 22W/gpm requirement first appeared
in earlier versions of ASHRAE Standard 90.1, there is no such size constraint,
and systems are modeled as primary only, which presumably would require less
pump power.
· My CHW system design experience is limited, but I’ll note that systems
in the north are typically designed with high percentages of glycol due to
freezing concerns, which increases the pumping power required.
Bill
________________________________
From:Paul Diglio [mailto:paul.diglio at sbcglobal.net]
Sent: Tuesday, November 16, 2010 9:00 PM
To: Bishop, Bill; John T. Forester; James Hansen
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Baseline Chilled Water Loop
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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