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Fan Availability Schedule

asked 2016-08-03 16:50:26 -0500

Adam Hilton gravatar image

updated 2016-08-04 06:10:35 -0500

I'm not seeing the fan availability schedule being respected by the OS to idf translator. The translator always assigns the air loop availability schedule to fan availability schedule. Anyone else experience this or am I missing something???

I skinned the loop down to just two fans, a setpoint manager, and an outdoor air system to try to figure it out.

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In OS Interface

Fan Settings:

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Air Loop Control Settings:

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In IDF Output (Using standard run process)

Fan:ConstantVolume,
Exhaust Fan,                            !- Name
Always On,                              !- Availability Schedule Name
0.7,                                    !- Fan Total Efficiency
250,                                    !- Pressure Rise {Pa}
0.5,                                    !- Maximum Flow Rate {m3/s}
0.9,                                    !- Motor Efficiency
1,                                      !- Motor In Airstream Fraction
Node 10,                                !- Air Inlet Node Name
Exhaust Air;                            !- Air Outlet Node Name

EDIT: This is related by the solution isn't applicable. If I want to disable one of the fans at certain times of the year shouldn't I be able to schedule it off using the fan availability schedule? Does that functionality not exist???

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answered 2016-08-05 14:15:21 -0500

The availability schedule of a fan in the context of AirLoopHVAC is ignored by design in OpenStudio. This is to avoid conflicts and confusion with the availability schedule.

The logic that is enforcing this behavior is located here, where OpenStudio converts the osm model into energyplus idf.

This is a little misleading on OpenStudio's part because it is showing the availability schedule in the inspector. This is because in the context of ZoneHVAC the fan availability schedule is in play, and the inspector policy that controls what fields you can access is not currently designed to be conditional based on the context of the fan you are looking at. Ideally OS would show the fan schedule when viewing Zone HVAC and not show it when you view a fan in AirLoopHVAC.

If there is a particular use case that OpenStudio's behavior is blocking, then I would like to hear more about what you are trying to accomplish.

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Thanks Kyle, makes sense. Simply put, I want to simulate exhaust fan operation in the winter but not the summer. Since there is heat recovery it needed to be in the air loop to capture the fan heat in the exhaust air that the HR sees.

Adam Hilton gravatar image Adam Hilton  ( 2016-08-05 14:44:18 -0500 )edit

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Asked: 2016-08-03 16:50:26 -0500

Seen: 1,175 times

Last updated: Aug 05 '16