[Trace-users] Appendix G Fan Energy

Jeremy Poling jpoling at epsteinglobal.com
Thu Oct 29 08:14:17 PDT 2009



The equations in Section G3.1.2.9 and Table G3.1.2.9 are only for the
baseline building.  For the baseline building, the supply CFM is used to
model the efficiency of all of the fans in the building based on
assumptions about minimum design characteristics.  If you are using the
equations, you should use the Supply CFM for the system, run through the
equations in Table G3.1.2.9 to determine the BHP for the baseline, then
run that through the equation in G3.1.2.9 to determine total fan power
in kW.  That value can then be input into Trace for fan power.


For the proposed building, you should use the actual rated fan kW based
on the fan power curve for your CFM and the fans specified.


As Bob stated, Trace does have an option where it will do the
conversions for the baseline building, but I typically have not used it.
I shy away from the "black boxes" in energy modeling when putting things
together for a LEED review team since ANYTHING is up for grabs when they
review the credit and if I can't explain a black box process they may
deny the entire credit.


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From: trace-users-bounces at lists.onebuilding.org
[mailto:trace-users-bounces at lists.onebuilding.org] On Behalf Of Snarski,
Sent: Tuesday, October 27, 2009 1:33 PM
To: trace-users at lists.onebuilding.org
Subject: [Trace-users] Appendix G Fan Energy


Hello, all.


I'm running an energy model (for LEED), and am having a particular
problem with the Fan Energy results.  I am using the actual fan
horsepower (for the supply and for the return fans) for the proposed
building, and the Appendix G equation in G3.1.2.9.  The results I'm
getting for the proposed design are considerably higher (about 31%) than
the baseline building.  This leads me to believe that I may be
misinterpreting the equation.  


As stated in the 90.1 Users manual, the equation accounts for supply,
return, relief, and exhaust fans.  However, I've been simply inputting
the Supply CFM into the equation.  Given that it accounts for all fans,
should I use the accumulated CFMs for each of those fans (i.e. if I'm
supplying 32,000, and returning 24,000, should I use 56,000 cfm)?


While I understand TRACE has the automatic baseline fan sizing
capability, I'm not sure I trust it completely, and would like to know
where the calculation comes from.


Thanks for any help you can offer!

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