90.1-2007 fan power pressure drop allowance question

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The 90.1-2007 fan pressure drop allowance includes credit for sound attenuation sections. Do you apply the credit for each silencer on a system? The system I am looking at has 3 silencers, one on the supply duct, one on each or two return ducts entering the AHU.

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Bldg simulation's picture
Joined: 2016-04-13
Reputation: 400

Dear Chris,
I have made the assumption that the pressure drop imposed by the silencers *on
the fan system* is the value that should be counted.

3 silencers on the supply side, for example, only affect the fan the same
as one silencer (assuming they're in parallel). If, as you say, there is
also one on the return side, then both will affect the fan and both should
be counted.

Bldg simulation's picture
Joined: 2016-04-13
Reputation: 400