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Modeling VAV Active Chilled Beams in EnergyPlus or OpenStudio

asked 2015-12-09 11:52:28 -0500

pflaumingo gravatar image

updated 2017-05-08 15:53:37 -0500

What approaches have people used in EnergyPlus or OpenStudio to model active chilled beams with a variable primary air flow rate? The EnergyPlus components are constant volume resulting in excess fan consumption and incorrect cooling/heating behaviour at the chilled beam. I've been thinking that using VAV with fan coil units that have their fan-power zeroed out is a good solution for space types where load strongly follows occupancy/ventilation requirements, but this breaks down in instances where load and ventilation aren't strongly coupled.

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Has any progress been made on a modeling approach for EnergyPlus or OpenStudio in modeling VAV or variable capacity chilled beams yet? I suspect no.

Neil B gravatar imageNeil B ( 2020-09-24 13:43:23 -0500 )edit

@Neil B not that I'm aware of. You can check the design docs on GitHub...

MatthewSteen gravatar imageMatthewSteen ( 2020-09-24 21:18:50 -0500 )edit

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answered 2016-03-08 05:39:23 -0500

Archmage gravatar image

I think your idea of using the fan coil unit with a VAV terminal is a good one. The problem you point out could be addressed by using AirTerminal:DualDuct:VAV:OutdoorAir. If you use just the outdoor air side you can modulate the outdoor air flow however you like.

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answered 2016-03-05 13:53:20 -0500

301_Hours gravatar image

This is a big issue that hasn't been resolved yet as most laboratory applications are variable air volume. There was a 2012 SimBuild paper on this topic.

The work around is to come up with an aggregate schedule for the air flow based on the flow rate it should be. Simply put 12 hours at 6 air changes per hour and 12 hours at 4 air changes per hour would be 5 air changes per hour for 24 hours. Of course this doesn't capture peak demand charges correctly if that's a factor in the design and over sizes the water side because you're only providing 5 air changes rather than 6.

Note that the induction ratio is not linear with air flow and drops off dramatically below 50% of design flow.

As far as I know only IES-VE does this correctly today.

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Asked: 2015-12-09 11:52:28 -0500

Seen: 1,149 times

Last updated: Sep 24