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RE: [EnergyPlus_Support] ASHRAE fan powers



I can’t recall what has been said in the past…..

Keep in mind:

·         The Pressure Rise field in all E+ fan objects is the product of fan and motor efficiency (EFFfan x EFF motor)

·         You can derive the pressure rise needed for a Baseline calculation; no iteration needed.  See if you can follow the attached spreadsheet for the derivation (Sorry; US units!)


The Building Performance Team
James V. Dirkes II, P.E., BEMP , LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653


From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Jean marais
Sent: Monday, May 30, 2011 11:41 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] ASHRAE fan powers



I know this topic has been disscussed to death, but I'm still a bit in the dark. I used energy plus results for constant fan volume maximum flow rates (assuming a pressure rise of 2000 Pa, 0.8 motor eff. and 0.7 fan eff.) as the input for my ASHRAE fan power calculation (G3.1.2.9) which spits out a rated input power after a fan efficiency and motor efficiency (0.7 and 0.8) have been applied. I then back calculate the ASHRAE fan pressure rise using the formula (trying from memory...correct me if I'm wrong Mr Dirks) dP=motor_Eff x fan_Eff x Wf(W)/Q to derive the
needed dP (delta P pressure rise) for each fan. I then re-enter the new pressure rise over the fan into energy plus and re-calculate the max air flow Q, and itterate this process hoping for a convergence.

How are others doing this to achive the rated fan power as per ASHRAE 90.1?

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d:\eudora\attach\Delta P Calc.xls
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