[Equest-users] Baseline Fan power calculation

Cam Fitzgerald cam at energyopportunities.com
Tue Mar 26 05:58:43 PDT 2013

So you are still confused. Hope this clarifies the process for you:


1. Example baseline fan power distribution calculations (other methods are
acceptable, but this is one of the most common approaches)


Proposed system:

Total fan kW (20+18+2.5=40.5 kW)

Design supply fan percent of total power (20/40.5=0.494)

Design return fan percent of total power (18/40.5=0.444)

Design exhaust fan percent of total power (2.5/40.5=0.062)


Baseline supply airflow calculated per Section G3.1.2.8 (Note: rarely a nice
round number, but I will use your number for this example) - 30,000 cfm

Assuming the baseline system is VAV (system types 5 - 8), and using a
pressure drop adjustment factor of 0.5 IWC (MERV 12 filter) , calculated
system fan power is 34.196 kW

Using the same ratios as the Proposed system, the Baseline fan power would
be: 16.893 kW supply; 15.183 kW return; and 2.120 kW exhaust.

You can use this power to determine the kW/cfm for each fan.


2. The supply fan may slightly increase the supply temperature, but this is
usually minimal and does not significantly impact the supply air

3. The baseline case prior to rotation should be used.

4. See response to #1.


Good luck!




From: vamshi ranga [mailto:vamshiranga at gmail.com] 
Sent: Tuesday, March 26, 2013 8:07 AM
To: Cam Fitzgerald
Cc: Nick Caton; 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

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> 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


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] On Behalf Of vamshi
Sent: Tuesday, March 26, 2013 3:27 AM
To: Nick Caton
Cc: 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> 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





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fax 913.345.0617

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From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of vamshi
Sent: Monday, March 25, 2013 8:17 AM
To: 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

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


Thanks in advance.






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