[Bldg-sim] 90.1-2007, Fan BHp and Filter Pressure Drop

[Rosenberg, Michael I]

My opinion is that if a designer "schedules" a fan bhp to meet a certain static pressure requirement, and then knowing that it will actually have to meet a higher static pressure (not as a safety factor but during normal operation) schedules a motor with a large enough nameplate hp to accommodate that, it is an attempt to get around the requirement in 90.1.
__________________________
Michael Rosenberg
Senior Commercial Buildings Energy Analyst
ENERGY & ENVIRONMENT DIRECTORATE
Pacific Northwest National Laboratory
2032 Todd Street
Eugene, OR 97405
(541) 844-1960
michael.rosenberg at pnl.gov
www.pnl.gov
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Ryan Hammond
Sent: Tuesday, March 23, 2010 1:31 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] 90.1-2007, Fan BHp and Filter Pressure Drop

All,

A colleague brought up an interesting point about filters and fan BHp.

Regarding 90.1-2007, Table 6.5.3.1.1A, Option 2, what is your interpretation of "bhp = the maximum combined fan brake horsepower" for an AHU?  And how does 90.1-2007 verify this?

90.1-2007 defines "fan system bhp" and "fan system design conditions"; however there isn't any clear mention of how exactly fan BHp is defined with respect to filters (100% loaded filter delta-p, 66% loaded filter delta-p, 33% loaded filter delta-p, etc.).  The fan system would still meet capacity requirements, just at a reduced filter pressure drop as scheduled.

For example, a designer could define (and schedule) the fan BHp to operate at a max of 66% of allowable filter pressure drop for reduced fan energy, yet schedule a fan motor to be able to meet the fully loaded filter pressure drop.

The ramifications of scheduling a lower fan BHp against 90.1-2007 is the proposed system will now be operating more "efficiently", compared to the baseline, assuming the filters are truly replaced at 66% of allowable filter pressure drop (which likely would never happen in the field!).

Any thoughts on this?  Anyone on the 90.1-2007 committee that could shed some insight?

Thanks,
Ryan

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R. Ryan Hammond   PE, HBDP, BEMP, LEED AP
Engineer
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