[Trace-users] Trace-users Digest, Vol 15, Issue 1

Kevin Caho kevin.caho at gmail.com
Tue Oct 27 17:39:28 PDT 2009


I had the same question previously and I would encourage you to check to
ECM/PRB sizing option yourself and verify that it is correct if this worries
you.  All you need to do is apply it for one simulation, open the "equipment
energy consumption" report, and do the hand calc with the cfm shown for each
fan and compare these values to the kW that Trace has calculated.  I think
you'll find that they are very close (within 1%).

You say your results are higher and I guess I'm not sure if you are
referring to the fan size or to the fan energy consumption.  In the
particular model that I have in front of me (using the ECM/PRB option) the
proposed is also higher. CFM by 16%, kWh by 19%, and kW by 23%.  This is not
surprising as the proposed case has 70% glass vs. 40% for the baseline so
their is more air needed to satisfy the load.  The kW/cfm however are nearly
the same.  I suggest checking items like that to make sure things are
proportional because your total % difference doesn't necessarily tell the
whole story.

My other thought is that you used the wrong units.  In your post you said
you used G3.1.2.9 to calculate the horsepower but your result from that
equation would be in watts.  If you used kW from that equation and entered
as hp in your 90.1 model, then you'd have 25% less power than you should
leaving your proposed more than 30% ahead.

Hopefully I answered your question somewhere in there.


Kevin Caho, LEED® AP




T: 312.360.4432  F: 312.360.4545

Kevin.Caho at Som.Com

On Tue, Oct 27, 2009 at 2:10 PM,
<trace-users-request at lists.onebuilding.org>wrote:

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> Today's Topics:
>   1. Appendix G Fan Energy (Snarski, Marty)
> ----------------------------------------------------------------------
> Message: 1
> Date: Tue, 27 Oct 2009 13:33:28 -0500
> From: "Snarski, Marty" <msnarski at shwgroup.com>
> To: <trace-users at lists.onebuilding.org>
> Subject: [Trace-users] Appendix G Fan Energy
> Message-ID:
>        <078AC5207CEDE145A8C7C74FFB3975A05470DE at DALEXC1.shwgroup.com>
> Content-Type: text/plain; charset="us-ascii"
> 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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Kevin Caho
T: 309.716.0084
kevin.caho at gmail.com
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