[Bldg-sim] Appendix G Fan Power

Jeremy Poling jpoling at epsteinglobal.com
Thu Jul 2 06:40:39 PDT 2009


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: 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
efranconi at archenergy.com
http://www.archenergy.com/


>>> "Rosenberg, Michael I" <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 
michael.rosenberg at pnl.gov 
www.pnl.gov 

From: 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 
Direct Phone 404-253-1466 | Direct Fax 404-253-1366 

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P Think GREEN before you print.

 

 

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