LEED - Future Expansion = Fan Power Oversizing

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I am working on a project currently that has oversized all of the VAV - AHU fans by approximately 25 HP (was 50 now is 75) to account for future expansion.  This expansion is not quanitfiable now, but is assured.  How do account for this in the proposed model since the baseline will only size the fans for current model inputs.  I am using Trace 700 with the autosize PRM selected.

Any help is greatly appreciated.



Nicholas Fonner
Energy Modeling Group
Henneman Engineering, Inc. | energy. focused.
1605 South State Street, Champaign, IL 61820
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www.henneman.com | nfonner@henneman.com

nfonner's picture
Joined: 2011-09-20
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This is an interesting concept. Given that the fans have VFD's, the maximum size of the fans isn't ever going to be utilized (in fact this should make them more efficient).

There are a few options. The simplest is that you simply enter the maximum hp for the supply fan of the proposed building under systems, fans tab (ie, if the fan is going to operate at 23.5 hp at design cfm, then enter 23.5 hp). The VAV curve will approximate the rest.

I would recommend doing this on all LEED projects that have VFD fans in the proposed. The reason is that fans only come in increments and they are always oversized. The baseline building doesn't really account for this fact since fans are sized by an equation that can yield a very specific number... ie 34.3 hp. (in a real building, you'd have to buy a 40 hp fan... and entering 40 hp in the model would cause more energy use).

As usual, let TRACE calculate the fan hp for the baseline.

Bob's picture
Joined: 2010-06-30
Reputation: 475