[Equest-users] Baseline Fan power calculation

James Hess JHess at tmecorp.com
Wed Mar 27 04:27:46 PDT 2013

With regards to LEED reviews, what we have done in the past, which has been successful, would be the following:

1.       Calculate Total Proposed Design Fan Power --> in your case: 20,000 + 18,000 + 2500 = 40500

2.       Calculate % Proposed Design Supply Fan Power --> 20,000 / 40,500 = 49.383%

3.       Calculate % Proposed Design Return Fan Power --> 18,000 / 40,500 = 44.444%

4.       Calculate % Proposed Exhaust Fan Power --> 2,500 / 40,500 = 6.173%

5.       Calculate Total Baseline Fan Power allowances per Appendix G, G3.1.2.9 (another way to check your fan power allowance calcs is the newest version of COMcheck, which includes the fan power calcs, finally :) )

6.       Apply the above percentages to the Total Baseline Fan Power allowance in order to breakout that allowance between Supply Fans, Return Fans, and Exhaust Fans.

7.       The above percentages are fixed and therefore have nothing to do with Baseline rotations.

8.       If you enter in the Baseline fan power as kW/CFM type input, the kW/CFM (per the G3.1.2.9 equations) is fixed and would not vary by rotation.  The total kW does vary, based on calculated CFM, which does vary by rotation (though not a lot).  eQuest is already taking this into account via the kW/CFM input.

Applying the percentages as described above is really the only assumption you can make for the Baseline model, other than to not break out the fan power at all, which I would argue is completely appropriate in many cases since they only include supply fans and some small exhaust fans.  In such cases, taking the time to break out the fan power in the Baseline could be considered a waste of valuable time because this has an insignificant effect on the overall results.  This is an area that I often simplify and ignore unless the project has significant return/exhaust fans (like a lab), or the GBCI reviewers make a fuss over this.  My guess is, however, that the new 1.4 spreadsheet will give us no choice but to break out the fan power as desired by the GBCI reviewers.

Hope this helps.



James A. Hess, PE, CEM, BEMP
Energy Engineer
TME, Inc.
Little Rock, AR
Mobile: (501) 351-4667

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of vamshi ranga
Sent: Tuesday, March 26, 2013 7:07 AM
To: Cam Fitzgerald
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Baseline Fan power calculation


Thanks, but it is difficult to understand (some confusion). Let's say the Proposed system has following specifications

Supply fan cfm = 40000
Supply fan Wattage = 20000
Return fan cfm = 35000
Return fan Wattage = 18000
Filter used = MERV 12
Exhaust fan cfm = 5000
Exhaust fan Wattage = 2500

And Baseline (0 deg orientation) has following specifications when simulated with default fan kW/cfm and 20 deg F difference,

Supply fan cfm = 30000
Supply fan Wattage = 15000
Return fan cfm = 25000
Return fan Wattage = 13000

1. Please tell me how to distribute kW/cfm in basecase and from where will I get baseline default exhaust specification?
2. Won't the change in baseline when we input calculated value in eQUEST due to heat gain
3. Should we take all the 4 orientations average cfm for calculating baseline cfms
4. Tell me how to calculate baseline fan power from above values

If, this example is confusing. I request you to give your own example for understanding.
I have been having doubt related to fan power calculation. I am eager to learn how to do it properly to avoid any GBCI comments.

Your valuable time put in resolving my doubt is appreciated.


On Tue, Mar 26, 2013 at 3:23 PM, Cam Fitzgerald <cam at energyopportunities.com<mailto:cam at energyopportunities.com>> wrote:

It seems there is much confusion on this issue. The Proposed fans are all modeled explicitly (with the fan power as designed). In the Baseline case each HVAC system fan power (Section G3.1.2.9)  is calculated using the supply airflow (Section G3.1.2.8) based on 20 F space to supply air temperature difference. If the Proposed system uses multiple fans, then the calculated system fan power is distributed among the fans in the Proposed design. Appendix G does not provide any guidance for how this power should be distributed among the system fans in the Baseline system, but usually projects use the same proportion of the total system fan power as the Proposed design. All the fan power can be modeled as a single supply fan, but that will apply all the heat gain from the fan to the supply airstream which may not be realistic for large systems. Note that exhaust fans in the Proposed design that operate continuously during occupied periods are considered part of the system and their power is included in the calculated Baseline fan power. Exhaust fans that operate intermittently are considered a process load and must be modeled identically in both cases. If the Proposed process exhaust fan motor is larger than one HP, the motor efficiency is regulated by  Section 10 and savings may be claimed for using high efficiency motors as compared to the minimum efficiency from Table 10.8.

Hope this helps!

Cam Fitzgerald

Energy Opportunities/a 7group company

From: equest-users-bounces at lists.onebuilding.org<mailto: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: Tuesday, March 26, 2013 3:27 AM
To: Nick Caton
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Baseline Fan power calculation

Dear Nick Caton,

Thank you very much for valuable inputs, from this it is clear that,

1. However there are different motors used in Proposed case for supply, return and exhaust with different kW/cfm, we need to use one single motor in with one kW/cfm in baseline case
2. In EAp2 Section 1 4 Tables of LEED under "Table 1.4.2", it asks for separate wattage of supply, return and exhaust fans in baseline case, So, there we need to enter as "Not Applicable"

Please let me know if my understanding is wrong.


On Mon, Mar 25, 2013 at 8:04 PM, Nick Caton <ncaton at smithboucher.com<mailto:ncaton at smithboucher.com>> wrote:
Hi Vamshi,

I advise carefully reviewing the footnotes under Table, which include procedure for determining baseline fan power adjustments.

1.       Pfan 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 CFMS and CFMD carefully at the cited Table.  A CFM quantity representing the airflow each element encounters (CFMD) 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."


[cid:489575314 at 22072009-0ABB]


Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036<tel:913.344.0036>
fax 913.345.0617<tel:913.345.0617>

From: equest-users-bounces at lists.onebuilding.org<mailto: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.


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