[Bldg-sim] chilled water pump power

[James V. Dirkes II P.E.]

Dear Dongyi,
 
I assign the actual flow (gpm or m3/s) and an equivalent head that results
in the ASHRAE pump power limit.  I've attached a spreadsheet which helps do
that for you more easily.
 
Note that I use EPlus and it assigns a fixed pump efficiency.  You'll have
to figure that out for your software.....
 

The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653

 

 

  _____  

From: xiao dongyi [mailto:xiaodongyi at hotmail.com] 
Sent: Friday, January 09, 2009 10:36 AM
To: imaor at pwienergy.com; wbahnfleth at psu.edu; jvd2pe at tds.net;
bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] chilled water pump power


Hi Itzhak,
 
If that is the assumption used to derive the 22 W/gpm, then how should I
divide it between the primary and secondary pump?

Thanks,
 
Dongyi


  _____  


Subject: RE: [Bldg-sim] chilled water pump power
Date: Fri, 9 Jan 2009 09:55:11 -0500
From: imaor at pwienergy.com
To: wbahnfleth at psu.edu; jvd2pe at tds.net; xiaodongyi at hotmail.com;
bldg-sim at lists.onebuilding.org



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   




 cid:971061017 at 30102008-281C
<http://gfx1.hotmail.com/mail/w3/ltr/i_safe.gif> 

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

 

  _____  

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
http://www.engr.psu.edu/ae/faculty/bahnfleth/ ,
http://www.engr.psu.edu/ae/iec

It is better to know less than to know so much that ain't so. - Josh
Billings

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