[Equest-users] Baseline Fan power calculation

[RobertWichert]

Thanks Bill,

I verified that the references you gave lead to the result of the 
calculation in the spreadsheet, but if the theoretical calculation below 
has any validity at all, the assumed fan efficiency in 90.1 is about 
8%.  I used a fan static pressure rise of .5 in. H2O.

So, this fan efficiency seems a little low to me.

You said "Fan efficiency is from ASHRAE 90.1, Table 10.8 as described in 
G3.1.2.9." but Table 10.8 is Fan Motor efficiency, which is about 85%.  
I have no problem with that, but to use the theoretical fan power 
equation I need the Fan efficiency.  Do you have any idea what fan 
efficiency is assumed in 90.1?

I also notice that the fan power calculation in 90.1 does not include a 
pressure rise component, which I find odd.  Is the pressure rise across 
the fan assumed somewhere?  From the checks described above, it appears 
to be about .5 in. H2O.  Does this seem reasonable?



Your thoughts?



Robert Wichert P.Eng. LEED AP BD&C
+1 916 966 9060
FAX +1 916 966 9068







===============================================

On 3/25/2013 8:01 AM, Bishop, Bill wrote:
>
> Robert,
>
> I'm sure Nick is typing furiously as I write this, but I'll probably 
> finish before him.
>
> Taking a quick look at the spreadsheet that Nick attached to his 
> email, it calculates baseline fan power using the method described in 
> Appendix G and 6.5.3.1.1. Fan efficiency is included in the P_fan 
> calculation per G3.1.2.9.
>
> Fan efficiency is from ASHRAE 90.1, Table 10.8 as described in G3.1.2.9.
>
> Regards,
>
> Bill
>
> *William Bishop, PE, BEMP, LEED AP **|**Pathfinder Engineers & 
> Architects LLP*
>
> Senior Energy Engineer
>
> 134 South Fitzhugh StreetRochester, NY 14608
>
> T: (585) 325-6004 Ext. 114F: (585) 325-6005
>
> wbishop at pathfinder-ea.com 
> <mailto:wbishop at pathfinder-ea.com>www.pathfinder-ea.com 
> <http://www.pathfinder-ea.com/>
>
> PSustainability -- the forest AND the trees.P
>
> *From:*equest-users-bounces at lists.onebuilding.org 
> [mailto:equest-users-bounces at lists.onebuilding.org] *On Behalf Of 
> *RobertWichert
> *Sent:* Monday, March 25, 2013 10:52 AM
> *To:* Nick Caton; equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] Baseline Fan power calculation
>
> I believe I have written about this in the past, but since this seems 
> to be on-topic, I'll bring it up again.
>
> The theoretical fan power equation, Fan BHP = (cfm x static press 
> "w.c.) / (6356 x fan efficiency) can be used to calculate the 
> theoretical fan BHP, but you need the fan efficiency.  This seems to 
> be NOT the way the BHP is being calculated by the spreadsheet that was 
> attached previously.
>
> Is there a reason for that?
>
> Was there an assumed fan efficiency used in the spreadsheet, and was 
> it based on anything particular, or just a conservative assumption?
>
>
> Thanks!
>
>
>
>
> Robert Wichert P.Eng. LEED AP BD&C
> +1 916 966 9060
> FAX +1 916 966 9068
>   
>   
>   
>   
>   
>   
>   
> ===============================================
>
> On 3/25/2013 7:34 AM, Nick Caton wrote:
>
>     Hi Vamshi,
>
>     I advise carefully reviewing the footnotes under Table 6.5.3.1.1A,
>     which include procedure for determining baseline fan power
>     adjustments.
>
>     1.P_fan represents the sum power of all fans in a given baseline
>     system (with exception to baseline systems #6/#8, fan powered VAV
>     boxes).
>
>     2.Again, there is not a separate supply/return power calculation
>     (see answer #1).  You can however account for adjustments present
>     in separate airstreams from the proposed design.
>
>     3.Probably not.  Review the difference between CFM_S and CFM_D
>     carefully at the cited Table.  A CFM quantity representing the
>     airflow each element encounters (CFM_D ) should be applied against
>     each pressure drop adjustment, not an 'aggregate' of supply+return.
>
>     You may also find the attached resource published by 7group
>     helpful to cement your procedural understanding of how to arrive
>     at the sum total for "A."
>
>     Regards,
>
>     ~Nick
>
>     cid:489575314 at 22072009-0ABB
>
>     **
>
>     *NICK CATON, P.E.*
>
>     SENIOR ENGINEER
>
>     Smith & Boucher Engineers
>
>     25501 west valley parkway, suite 200
>
>     olathe, ks 66061
>
>     direct 913.344.0036
>
>     fax 913.345.0617
>
>     www.smithboucher.com__
>
>     *From:*equest-users-bounces at lists.onebuilding.org
>     <mailto:equest-users-bounces at lists.onebuilding.org>
>     [mailto:equest-users-bounces at lists.onebuilding.org] *On Behalf Of
>     *vamshi ranga
>     *Sent:* Monday, March 25, 2013 8:17 AM
>     *To:* equest-users at lists.onebuilding.org
>     <mailto:equest-users at lists.onebuilding.org>
>     *Subject:* [Equest-users] Baseline Fan power calculation
>
>     Hi All,
>
>     I have a doubt regarding calculating fan power as per ASHRAE
>     90.1-2007.
>
>     My proposed system has, supply return
>     and exhaust fans separately with kW and cfm mentioned for each fan.
>
>     So, for calculating baseline fan power,
>
>     1. should I calculate it separately for each fan type?
>
>     2. can I take pressure drop adjustment both in supply and return
>     fan power calculation?
>
>     3. should I sum all the cfms of supply, return and exhaust and
>     than apply pressure drop adjustments to aggregated cfm.
>
>     Kindly help me out in solving the doubt. If you have any example
>     fan power calculations, or web links those could guide me
>     regarding this, plz do share them.
>
>     Thanks in advance.
>
>     Regards,
>
>     Vamshi.
>
>
>
>
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