[Bldg-sim] System Fan Power in Appendix G

[Kendra Tupper]

Option 1 ­ the user¹s manuals are a bit more clear, and specify that the its
is the supply cfm that should be used to calculate the fan power. This fan
power includes supply, return and exhaust.


On 1/20/09 11:29 AM, "Zeng, Ming" <mzeng at leoadaly.com> wrote:

> My understanding is option 1. The fan energy in that formula is the sum of all
> the fan horse power. Search the board, I think there is a previous email from
> Michael Rosenberg talking about the fan energy. Hope this helps.
>  
> 
> Ming Zeng, PE, LEED® Accredited Professional
> 
> Mechanical Engineer
>  
> 
> 
> 
> 730 Second Avenue South, Suite 1100, Minneapolis, MN 55402-2455
> 
> T 612.338.8741    F 612.338.4840    D 612.341.9539
> 
> www.leoadaly.com <http://www.leoadaly.com>     MZeng at leoadaly.com
>  
> Please consider the environment before printing.
> 
> From: bldg-sim-bounces at lists.onebuilding.org
> [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Mike Kaufman
> Sent: Tuesday, January 20, 2009 12:16 PM
> To: bldg-sim at lists.onebuilding.org
> Subject: [Bldg-sim] System Fan Power in Appendix G
>  
> Hi All,
>  
> I have a specific question about using Appendix G3.1.2.9 to calculate baseline
> system fan power (I have already searched previous posts and could not find
> the answer I¹m looking for).  So, the Appendix G section reads as follows:
> System fan electrical power for supply, return, exhaust, and relief (excluding
> power to fan powered VAV boxes) shall be calculated using the following
> formulas.  I understand the formulas, which essentially use a fan CFM to
> determine a brake horsepower BHP, which is then used to calculate the fan
> power (Watts), but my question is this:  Supposing you have an HVAC system
> with supply, return, and small exhaust fans (in restrooms, for example) ­ how
> do you calculate the power to each fan?
>  
> Option 1:  Use your supply fan cfm to calculate a power, say it comes to 10
> kW, and use this as your total ³system² fan power.  This 10 kW, being your
> whole system power, is then distributed among all of your system fans however
> you desire (For example, supply fan power = 5 kW, return fan power = 4 kW,
> exhaust fan power = 1 kW, for a total of 10 kW for the fan system)
>  
> OR
>  
> Option 2:  Use each supply, return, and exhaust fan cfm to separately
> calculate an individual kW for each fan (For example, supply fan power = 10 kW
> using the supply cfm, return fan power = 9 kW using the return cfm, exhaust
> fan power = 1 kW using the exhaust cfm, for a total of 20 kW for the whole fan
> system)
>  
> Obviously, you will have much more fan energy in a baseline system calculating
> fan power with Option 2.  Does anyone have a specific example they can share
> of a fan system calculation that was accepted by USGBC for an EAc1 energy
> model?
>  
> Thanks for your help!
> Mike
>  
>  
>        Mike Kaufman, Building Performance Engineer 130 W. 5th Avenue, Denver,
> CO 80204  (NOTE NEW ADDRESS) t 303.278.1532x206 | f 303.278.8533 |
> ambient-e.com <http://www.ambient-e.com/>
>  
>  
> 
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