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Scheduled fan flow rate in multizone model

asked 2017-06-02 16:55:45 -0500

updated 2017-06-05 00:42:10 -0500

I can't seem to get this right... What is the correct way to modify the volume flow rate of a supplyfan (Fan:ConstantVolume) in an airloop based on a time schedule to simulate a four mode operating switch (off/night/day/boost ) in a multizone model? There are no heating/cooling coils in the system, only a HeatExchanger before the OutdoorAir:Mixer. The system should operate with 100% fresh air. At the moment I have AirTerminal:SingleDuct:Uncontrolled in every zone (sum of the max terminal flow rates = max flow rate of fan:constantvolume).

summarizing: How do I make an airloop operate at 50% of max flow rate between time x:xx - y:yy, 75% between time x:xx2-y:yy2 etc.

Is there an example file for a similar case?

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answered 2017-06-02 20:11:12 -0500

From the I/O guide on Fan:ConstantVolume:

"This object models a constant air volume fan that is intended to operate continuously based on a time schedule. This fan will not cycle on and off based on cooling/heating load or other control signals (Ref: Fan:OnOff)."

The Fan:ConstantVolume has only two settings - on or off. You can't modulate flow.

The Fan:OnOff object can do this, but to do so "...this object must be used as part of a compound object that allows multiple fan speeds". That doesn't include an AirLoopHVAC.

The solution is to use a Fan:VariableVolume object, adjust the coefficients to match your fan, and then use the various schedules in the Controller:OutdoorAir object to force a specific air flow rate per your schedule.

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@mdahlhausen. Thanks for your answer, but the flowrate inside the air loop is still not following the outside air flow rate. I've attached a graph and a picture of my e+components. Am I missing a component to link the airflowrates inside the airloop to the outside airflow rates? I also tried to use setpointmanager scheduled to control the flowrate at the mixed air node and the terminal outlets, but that didn't work. I would like to have the orange curve follow the blue one.

BBel gravatar image BBel  ( 2017-06-05 00:41:49 -0500 )edit

which schedules in the Controller:OutdoorAir object did you set?

mdahlhausen gravatar image mdahlhausen  ( 2017-06-05 11:20:45 -0500 )edit
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answered 2017-06-05 03:24:15 -0500

updated 2017-06-05 06:28:23 -0500

An EMS actuator to override the fan flow rate with calling point InsideHVACSystemIterationLoop did the trick. However I can't believe that there isn't a better way to do this, so feel free to add your answers.

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Asked: 2017-06-02 16:55:45 -0500

Seen: 161 times

Last updated: Jun 05 '17