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 Fellow7group / Energy Opportunities
LEEDuser Expert
5907 thumbs up
May 21, 2013 - 4:28 pm
What software are you using?
HOUCINE TLEMSANI
Mechanical DesignerMEP Engineering Solutions, Inc
14 thumbs up
May 21, 2013 - 4:40 pm
trace 700
Anil Bhari
Min engineering inc3 thumbs up
May 21, 2013 - 10:13 pm
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
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5907 thumbs up
May 22, 2013 - 10:54 am
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?
HOUCINE TLEMSANI
Mechanical DesignerMEP Engineering Solutions, Inc
14 thumbs up
May 22, 2013 - 10:58 am
thanks Marcus and Anil that's easy way of doing it.