Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question

change from Fan:ConstantVolume to Fan:OnOff

asked 2014-12-10 17:17:42 -0500

Alex Vlachokostas gravatar image

updated 2015-01-09 12:36:32 -0500

Hi everyone, I currently have a Fan:ConstantVolume in a single thermal zone model: I want to change the Fan:ConstantVolume which does not cycle to a Fan:OnOff which cycles with heating/cooling. Therefore, after reading the InputOutput Reference document, I just substituted the Fan:ConstantVolume with the Fan:OnOff object.

However, I get the following severe error: * Severe * GetAirPathData: AirLoopHVAC = "SYS-1". * ~~~ * ..Invalid Air Loop Component Type = "FAN:ONOFF". * ~~~ * ..Air Loop Component Name = "SYS-1 SUPPLY FAN". * ~~~ * ..reference Branch = "SYS-1 MAIN BRANCH". * ~~~ * ...This component may only be referenced by a parent component such as AirLoopHVAC:Unitary:Furnace:HeatCool or similar. * Fatal * GetAirPathData: Errors found retrieving input for AirLoopHVAC.

Apparently there are more objects that I have to define. Any thoughts?

Thank you very much. I appreciate your help.


edit retag flag offensive close merge delete

1 Answer

Sort by ยป oldest newest most voted

answered 2014-12-10 17:44:26 -0500

updated 2014-12-10 17:45:28 -0500

You cannot just replace Fan:ConstantVolume with Fan:OnOff on an AirLoopHVAC, otherwise you get the error message you see.

Fan:OnOff must be used as part of a compound object, meaning it needs to be used in a AirLoopHVAC:Unitary:Furnace:HeatCool, ZoneHVAC:PackagedTerminalAirConditioner, etc.

That said, if you are using EnergyPlus 8.1 or higher you can use AirLoopHVAC:UnitarySystem. This will allow you to embed a Fan:OnOff on an AirLoopHVAC.

edit flag offensive delete link more


And with any of these unitary or packaged equipment types, you use the Supply Fan Operating Mode Schedule to indicate when the fan should run in cycling mode (0) or continuously (1).

MJWitte gravatar imageMJWitte ( 2014-12-10 20:52:05 -0500 )edit

Thank you both for your prompt and very helpful postings.

Alex Vlachokostas gravatar imageAlex Vlachokostas ( 2014-12-12 15:24:36 -0500 )edit

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer


Question Tools

1 follower


Asked: 2014-12-10 17:17:42 -0500

Seen: 137 times

Last updated: Dec 10 '14