[Bldg-sim] chilled water pump power
James V. Dirkes II P.E.
jvd2pe at tds.net
Thu Jan 8 17:19:32 PST 2009
Dear Bill,
I don't think I follow your logic. If the total plant head (primary plus
secondary) is ~100 ft., and assuming that water flow is about the same for
both primary and secondary, then your calcs indicate that 22W is a
reasonable number for the pumping system efficiency.
This is essentially the same scenario that I intended to use below. The
primary side would use, say, 30ft of head and the secondary side would use
~70ft. If the total head is greater than that, it (obviously) becomes
tougher to comply with 22W / gpm.
That said, I haven't modeled a System #7 or 8 per Appendix G yet, so I'm
just hypothesizing!
p.s., I think it will be tough to get a combined wire-water efficiency of
85%!
The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
_____
From: William Bahnfleth [mailto:wbahnfleth at psu.edu]
Sent: Thursday, January 08, 2009 7:52 PM
To: James V. Dirkes II P.E.; xiaodongyi at hotmail.com;
bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] chilled water pump power
I sincerely doubt it.
A fairly typical total pump head for plant and distribution for a
primary/secondary systems might be 100 -120 ft. (Note, I am not saying that
is GOOD practice, but it is typical. One can generally do better.)
Let's say that the overall efficiency of pump, motor, and drive is ~85%.
If we use the common engineering approximation HP = (Q*H)/(3960*eta_t), and
given that 1 HP = 745.7 W, the power associated with 1 gpm and 100 ft wg
head is
W = 745.7*(1*100)/(3960*0.85) = 22.15
I cannot think of a reasonable scenario under which 44 W/gpm could be
construed to represent minimally acceptable practice.
Bill Bahnfleth
At 07:14 PM 1/8/2009, James V. Dirkes II P.E. wrote:
Good question! My guess is that each pump may be 22W / gpm. Since they are
required to use variable speed drives (for >300T), it won't affect energy
adversely.
There may be an ASHRAE clarification on this topic; have you checked with
them?
The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653<?xml:namespace prefix = o ns =
"urn:schemas-microsoft-com:office:office" />
_____
From: bldg-sim-bounces at lists.onebuilding.org [
<mailto:bldg-sim-bounces at lists.onebuilding.org>
mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of xiao dongyi
Sent: Thursday, January 08, 2009 6:18 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] chilled water pump power
Hi,
I have a question regarding the chilled water pump power calculation in
ASHRAE 90.1 Appendix G:
ASHRAE 90.1 Appendix G Paragraph G3.1.3.10 requires that "The baseline
building design pump power shall be 22 W/gpm.". If the chilled water pumping
system is a primary-secondary system, how does this rule apply? i.e. does
the 22 W/gpm apply to the primary pump, secondary pump, or both? Or, do I
need to divide it between the primary and secondary pump?
Your suggestions will be greatly appreciated.
Thanks,
Dongyi
_____
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<http://windowslive.com/howitworks?ocid=TXT_TAGLM_WL_t1_allup_howitworks_012
009> how it works.
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William P. Bahnfleth, PhD, PE, FASHRAE
Professor of Architectural Engineering and Director, Indoor Environment
Center
Penn State / 104 Engineering Unit A / University Park, PA 16802 USA
voice: 814.863.2076 / fax: 814.863.4789 / e-mail: wbahnfleth at psu.edu
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