[Bldg-sim] pro-rating fan power to supply/return fans per 90.1-2007?

[Paul Erickson]

Paul,

I think your point about "proportioning power (kW) across fans with different operation" is exactly the intent of this addition to 2010 (though perhaps I'm twisting your angle on it).  The intent of it is to provide consistency in the review process and undue penalty with regards to fan power.  Using your example, if the Proposed design uses CAV exhaust fans and VFD driven supply & return fans, then the Baseline should as well.  Some modelers (because the requirement has been unclear to date) put all of the fan kW on the Supply fan for the Baseline, which would skew the results so as to under-account for the Baseline energy/cost.    Others may actually game the system and place the bulk of the allowable kW on the CAV fan and not the Baseline's SA and RA fans.  It can go either way so I think this new clarity is helpful.

I wasn't sure about the last part of your comment but assumed you were referring to "professional judgment" when selecting fans in the design process.  Did I miss an important modeling insight?

Paul

Paul Erickson  LEED(r) AP BD+C
Sustainable



AEI | AFFILIATED ENGINEERS, INC.
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P: 608.236.1112 | F: 608.238.2614
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From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Paul Riemer
Sent: Tuesday, March 15, 2011 4:54 PM
To: 'Andrew Craig'; James Hansen; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] pro-rating fan power to supply/return fans per 90.1-2007?

Mike Rosenberg's section is a welcome improvement but it is still a challenging aspect.
You could be proportioning power (kW) across fans with different operation.  For example:

-          CAV exhaust fan vs. VFD driven supply & return fans

-          "Powered exhaust" fans that only operate to provide relief during economizer mode vs. normal supply fans

In some instances, applying a bit of professional judgment will get better results in terms of fan energy (kWh) and fan heat (DT and resultant heating and cooling loads).

Paul Riemer, PE, LEED AP
DUNHAM
Celebrating 50 Years of Service

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Andrew Craig
Sent: Tuesday, March 15, 2011 4:24 PM
To: James Hansen; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] pro-rating fan power to supply/return fans per 90.1-2007?

James---

This was discussed recently in the posts.  See the attached response from last Tuesday.

Mike Rosenberg commented that this is being addressed in the upcoming 90.1-2010 as such:

G3.1.2.10.1 The calculated system fan power shall be
distributed to supply, return, exhaust, and relief fans in the
same proportion as the proposed design.

Regards,

Andrew Craig PE, LEED AP
Project Mechanical Engineer

INTERFACE ENGINEERING
email andrewc at interfaceeng.com<mailto:andrewc at interfaceeng.com>
direct 503.382.2696

www.interfaceeng.com<http://www.interfaceeng.com/>

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of James Hansen
Sent: Tuesday, March 15, 2011 12:05 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] pro-rating fan power to supply/return fans per 90.1-2007?

App G says that if the proposed building has return fans, the baseline building is to be modeled with them as well, sized either at the minimum required to ensure ventilation, or 90% of the supply volume, whichever is greater.  And the fan power calculations show that the KW allowance is for all supply, return, exhaust and relief fans combined.

How do you generally pro-rate the fan power between supply and return fans in the baseline model?  Ultimately it probably doesn't make too much difference, but is there an actual ruling that tells you how to do this?

Thanks,

GHT Limited
James Hansen, PE, LEED AP
Senior Associate
1010 N. Glebe Rd, Suite 200
Arlington, VA  22201-4749
703-338-5754 (Cell)
703-243-1200 (Office)
703-276-1376 (Fax)
www.ghtltd.com<http://www.ghtltd.com/>


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