making air loop constant volume fan cycle

asked 2022-03-05 14:22:50 -0500

mattkoch's avatar

updated 2022-03-07 19:25:18 -0500

For an AirLoopHVAC, it seems that one cannot make a FanConstantVolume cycle (at night or otherwise). Further, it seems one cannot insert a FanOnOff - which apparently can cycle - via OpenStudio-2.9.1 or OpenStudioApplication-1.2.1 to replace a FanConstantVolume.

Even further, it seems that the workaround is to use an AirLoopHVACUnitarySystem instead. However, there seem to be harsh limitations on the use of setpoint managers for such, basically limiting one to the "Load" control method and foregoing a setpoint manager approach altogether?

So, in summary, I currently believe one can either have a set point manager but no fan cycling, OR one can have a cycling fan but no setpoint manager? Is this overly simplified? Is there a way - with just OpenStudio-2.9.1 or OpenStudioApplication-1.2.1 - to have a cycling fan AND a setpoint manager.

With setpoint manager I mean one for the whole loop, usually placed on the outlet node of the supply half. Also, if there is a way, can that be applied to FanVariableVolume also?

Version: image description

Air Loop HVAC: image description

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Is there a reason why you are still using OS 2.9.1? The OpenStudio App 1.2.1 uses OpenStudio 3.2.1, and for sure you can add a FanOnOff on an AirLoopHVAC, are you getting some type of warning when you try to drag and drop it?

Luis Lara's avatar Luis Lara  ( 2022-03-07 10:21:47 -0500 )edit

Thank you Luis Lara. That would have been my best guess as well. But as you can see in the above screenshots (added to my original post), there are only four fan types available to drop down from and FanOnOff is not one of them. I seem to recall that at some point, in earlier versions of OS, there might have been such, but I can no longer find it in OpenStudioApplication-1.2.1? What am I missing? How did you get this fan type to show up in your OpenStudioApplication-1.2.1?

Also, I am only using OpenStudio-2.9.1 to generate geometry under SketchUp Make 2017.

mattkoch's avatar mattkoch  ( 2022-03-07 19:31:50 -0500 )edit

I confirmed that the following measure snippet does work and a fan does show up in the diagram of the OpenStudioApplication HVAC tab:

test_fan = OpenStudio::Model::FanConstantVolume.new(model)
test_fan.addToNode(air_loop.supplyOutletNode())

However, the following measure snippet seems to work (no error reported) but a fan DOES NOT show up in the diagram of the OpenStudioApplication HVAC tab:

test_fan = OpenStudio::Model::FanOnOff.new(model)
test_fan.addToNode(air_loop.supplyOutletNode())

Is this by design or error? If by design, why is the FanOnOff discriminated against?

mattkoch's avatar mattkoch  ( 2022-03-09 09:27:36 -0500 )edit

I am having the same issue. Have you found any solutions? I thought a constant volume fan would cycle on and off with the system as it called for heating and cooling, but this is not the case. I guess I am in search of the OS:FanOnOff that does not show up in my HVAC Systems component library.

Adam Sustainable's avatar Adam Sustainable  ( 2024-02-14 19:05:09 -0500 )edit
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