[Bldg-sim] Appendix G Fan Power

[James Hess]

We got a review comment on a recent LEED project asking us to break down the baseline HVAC power into components even though there is no direction, or requirement, from 90.1-2004 to do so.

Can someone please help me understand why this would be necessary?

LEED guidelines say we have to model per Appendix G, but Appendix G doesn't say we have to do this.

I do not think it is necessary to do this as the baseline total fan energy consumption numbers would still be the same.

The equation in Appendix G is meant to give a total allowance (for each system) for supply, return, and exhaust fans. It doesn't matter if we break the allowance down into components or not as the total fan energy consumption remains the same. Therefore, there is no value in doing this.

If we did break the fan energy numbers into components, how would we do that given that there is no direction from ASHRAE or LEED on how to do this?

Thoughts?

Regards,

James A. Hess, PE, CEM
Energy Engineer
TME, Inc.

On Jul 2, 2009, at 8:41 AM, "Jeremy Poling" <<mailto:jpoling at epsteinglobal.com>jpoling at epsteinglobal.com<mailto:jpoling at epsteinglobal.com>> wrote:

This issue will start to become a problem for anyone running energy models for LEED projects – reviewers on the new review teams are asking to see the total fan power for the baseline broken into individual components and reported as such in the template for Energy and Atmosphere Credit 1.  The 90.1-2004 User’s Manual is also silent on the issue; however it raises another issue.  In the example (Example G-J on page G-28) the calculations use total building supply CFM for an 80,000SF medical office building.  Since the baseline is System 5 in that example and there would be multiple zones for the baseline, it appears that the equation should be used for the whole building only and not individual systems.  Is this how you are applying the formulas?  The user’s manual notes that fan powered VAV boxes are NOT included in the total fan power number as calculated from G3.1.2.9.

Jeremy R. Poling, LEED AP
Senior Sustainability Analyst
Strategic Services
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From: <mailto:bldg-sim-bounces at lists.onebuilding.org> 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 Ellen Franconi
Sent: Thursday, July 02, 2009 7:37 AM
To: Vikram Sami; Bldg-Sim; Michael I Rosenberg
Subject: Re: [Bldg-sim] Appendix G Fan Power

At my firm, we proportion the baseline total fan power determined as an aggregated W/CFM based on  the hp assigned to the fan motors (supply, return, exhaust) in the design documents. Of course this assumes that your baseline and your proposed design have a one-to-one fan correspondence.
Ellen


Ellen Franconi, Ph.D., LEED AP
Senior Energy Analyst
Architectural Energy Corporation
2540 Frontier Avenue
Boulder, CO 80301
tel. 303-444-4149
fax 303-444-4303
<mailto:efranconi at archenergy.com><mailto:efranconi at archenergy.com>efranconi at archenergy.com<mailto:efranconi at archenergy.com>
<http://www.archenergy.com/><http://www.archenergy.com/>http://www.archenergy.com/


>>> "Rosenberg, Michael I" <<mailto:michael.rosenberg at pnl.gov>michael.rosenberg at pnl.gov<mailto:michael.rosenberg at pnl.gov>> 7/1/2009 4:48 PM >>>
You have calculated the kW/cfm correctly according to the 2004 version of Appendix G. The allowance actually goes up a little in 2007, for your case. As for the second part of your question, no you do not apply the same kW/cfm to the exhaust fan. The calculated allowed fan power the total allowed power for all fans that are part of the system, including the exhaust fan. The cfm component is based on the supply fan cfm only. Unfortunately, Appendix G gives no direction on how to divide the allowed fan power up among the various fans in the system.

Mike

__________________________
Michael Rosenberg
Senior Commercial Buildings Energy Analyst
ENERGY & ENVIRONMENT DIRECTORATE
Pacific Northwest National Laboratory
2032 Todd Street
Eugene, OR 97405
(541) 844-1960
<mailto:michael.rosenberg at pnl.gov>michael.rosenberg at pnl.gov<mailto:michael.rosenberg at pnl.gov>
<http://www.pnl.gov>www.pnl.gov<http://www.pnl.gov>
From: <mailto:bldg-sim-bounces at lists.onebuilding.org> 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 Vikram Sami
Sent: Wednesday, July 01, 2009 3:03 PM
To: Bldg-Sim
Subject: [Bldg-sim] Appendix G Fan Power

G3.1.2.9 Gives you a formula for calculating system fan electrical power for supply, return, exhaust and relief. Lets sat I have a zone with a PSZ-HP that has a supply volume of 1500 cfm. Using this formula along with table G3.1.2.9 I get a fan horse power of 1.29 and kW of 1.17. This equates to 0.00078 kW/cfm – which seems really high.

The second part to my question is assuming I have 500cfm of exhaust in this zone, do I apply the same kW/cfm to the exhaust fans as well as the return fans? It seems that the lower the fan volume the more inefficient the Appendix G values get from these tables.

Any guidance would be much appreciated.

Vikram Sami, LEED AP
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