[Bldg-sim] chilled water pump power

Itzhak Maor imaor at pwienergy.com
Fri Jan 9 06:55:11 PST 2009


Hello Bill
 
You are correct. The 22 W/GPM is combined Primary and Secondary pumping.
The assumption that used to derive this number is total head of 75'.
 
Thanks
 
Itzhak
 

Itzhak Maor Ph.D., P.E., C.E.M 
Manager, Energy Efficiency Services 

Global Workplace Solutions 
Building Efficiency | Energy Services 

Johnson Controls, Inc. 
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________________________________

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of William
Bahnfleth
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
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________________________________

	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
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