[Bldg-sim] chilled water pump power

[Zhuolun Chen]

Hi, Itzhak
I want to know that if the 22 w/gpm is the total of primary and secondary pumping, how can I divide  this total value into the two system? Is there a factor or something I can use?

ZL Chen


From: Itzhak Maor 
Sent: Friday, January 09, 2009 7:55 AM
To: William Bahnfleth ; James V. Dirkes II P.E. ; xiaodongyi at hotmail.com ; bldg-sim at lists.onebuilding.org 
Subject: Re: [Bldg-sim] chilled water pump power


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. 
1617 JFK Blvd., Suite 1140 | Philadelphia, PA 19103 

Tel.: (215) 241-9111 ext. 14 | Fax: (215) 241-0113 

Cell: (215) 767-4582

 

Itzhak.Maor at jci.com | www.JohnsonControls.com   






Please note my new email address, effective November 1st (and useable in the interim).





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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
  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] 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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