I'm wondering how variable air volume fans are controlled in Open Studio. End use, I am trying to model VFDs on HVAC fans (not exhaust fans) and I am wondering how a VFD on a CAV fan would operate differently/similarly to a VAV fan?
The Fan:VariableVolume module uses a polynomial relationship to set fan power as a function of flow rate only. Because it's only a function of flow rate, the fan is not controlled to a static pressure setpoint as it would typically in a real building. The flow rate is controlled by the terminal controllers, and this flow rate is sent to the fan to calculate the power usage based on the polynomial relationship. I believe the default in Open Studio corresponds to a VFD driven fan with a fairly aggressive static pressure reset. You could also modify the coefficients to model inlet vane or discharge damper control.
The Fan:ConstantVolume module doesn't have this relationship, so it consumes the same power regardless of the system flow rate.
I have a follow up question from this earlier thread. I'm not sure where the default coefficient values in the fan power curve come from? If anyone could point me in the right direction, that would be greatly appreciated.
@FrontierAssoc104 You may want to post this as a separate question since it will get more visibility that way.
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