[Bldg-sim] chilled water pump power

[James V. Dirkes II P.E.]

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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__________

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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