PVAV Fan Energy

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Hello all,

Does anyone know exactly what's included in the "Total SYSTEM/ZONE fan (supply, return, exhaust) elec consump (kw)" value in hourly reports? I am having an issue with my model where I have unexpectedly high fan energy use and when I trend the aforementioned point along with the supply and return fan power, the total system/zone fan kW is much greater than the sum of the supply and return fan kW. In some cases 10 times greater. I'm using PVAV system type with enthalpy wheels. I've zeroed out the dP across the wheel because I have a given fan capacity. No fan-powered boxes in the zones. No exhaust fans in the zones. I'm stuck trying to determine where the extra fan energy is coming from.

Any help would be greatly appreciated.

Thanks,
Joe

Joe Bliss

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Joined: 2012-06-05
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I would look into the enthalpy wheels more. I usually zero out the kW/cfm
on the wheels if the fan energy is already accounted for elsewhere, but
still leave a 0.0001 dP accross the wheel. Also, try leaving the CFMs at
default in the supply and exhaust inputs for the wheel. Occasionally these
cause issues because the fan is trying to get more airflow from the fan.

Hope that helps,
Rob H

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Joined: 2011-02-14
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Fan energy attributable to the enthalpy wheels will appear in the ERV Energy Recovery Summary reports. It is also included (but not broken out) in the SS-H, SS-L and SS-M reports, except for the bottom portion of SS-L where the supply and return fans are broken out.
Hint: For the SS-L and SS-M reports,
Total fan electric (FE) energy = FE during heating + FE during cooling + FE during floating - FE during heat & cool

Regards,
Bill

[Senior Energy Engineer 28Jun2012]

Bill Bishop's picture
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Joined: 2012-02-25
Reputation: 7

It doesn't appear to be using any additional fan power according to the ERV report (unless I'm reading it wrong - 0.84 kW for the wheel motor, 0 kW for fans).

[cid:image001.jpg at 01CDD859.FDA32970]

It also appears to be happening only when the ERV is off.

[cid:image007.jpg at 01CDD859.FDA32970]

Thank you again for your help and quick responses.
Joe

Joe Bliss

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