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NC-2009 EAp2:Minimum Energy Performance

VAV FAN POWER BOX MODELING

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HOUCINE TLEMSANI
Mechanical Designer
MEP Engineering Solutions, Inc
LEEDuser Basic Member
8 thumbs up

I am working on a project where the base line hvac system is type 6 VAV with fan power boxes. ASHRAE 90.1 requires the fan power box CFM to be sized at 50% of the peak CFM at 0.3 W/CFM. There is no guidance in 90.1 user manual on how to comply with this requirement, further more when we asked the modeling software help line they said that it can’t be done and that the software is automatically sizing the fan power box CFM at 50% of the system heating CFM not the cooling CFM. This comment keeps coming almost on every project with this type of system. Any input on how to deal with this issue?

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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Tue, 05/21/2013 - 20:28

What software are you using?
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HOUCINE TLEMSANI
Mechanical Designer
MEP Engineering Solutions, Inc
LEEDuser Basic Member
8 thumbs up

Tue, 05/21/2013 - 20:40

trace 700
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Anil Bhari
Min engineering inc
LEEDuser Basic Member
2 thumbs up

Wed, 05/22/2013 - 02:13

I am also creating baseline with system-6. For system i have selected FP VAV with reheat, than for FP vav box, I took 50 % of Total CFM (Cooling) and multiply 50 % of CFM by 0.3 to get wattage. And input total wattage into secondary supply fan in Fan tab. After reading above comment it sounds like, it is more complicated than what i did. Any suggestion? Thank you
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Wed, 05/22/2013 - 14:54

Just to be clear the value is 0.35 W/cfm. We are not aware of any limitations in Trace for accurately modeling this issue. Anil's approach sounds right to us but we are not Trace experts. Consult the help desk again or post your issue on the Trace users group at onebuilding.org. Any other thoughts?
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HOUCINE TLEMSANI
Mechanical Designer
MEP Engineering Solutions, Inc
LEEDuser Basic Member
8 thumbs up

Wed, 05/22/2013 - 14:58

thanks Marcus and Anil that's easy way of doing it.

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