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Modelling Ceiling heating/cooling with EnergyPlus

asked 2022-11-22 03:13:33 -0600

blackbody's avatar

updated 2022-11-22 08:16:35 -0600

Hi.

I have a Revit model that contains ceiling heating/cooling (using BEKA capillary tube mats - see https://www.beka-klima.de/en/heating-...). It is somewhat like floor heating, except different. :-)

Heating only via radiation (and then the heated surfaces radiate and heat by convection) and cooling via convection (contrary to floor heating where not much would happen, here the cooled air drops from the ceiling).

I'm asking - as an investor - for pointers how to model that, because all the people I've hired so far and who claim to be skilled in EnergyPlus simply did so "using a radiant floor as it's the closest to BEKA heating", which I am afraid is way off.

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answered 2022-11-22 09:04:00 -0600

For EnergyPlus, the ZoneHVAC:LowTemperatureRadiant:VariableFlow object and ZoneHVAC:LowTemperatureRadiant:ConstantFlow object would the closest thing to BEKA capillary tube mats (no model objects match this scenario exactly). These can be assigned to any type of surface (floor, wall, ceiling), and can have a connection to both hot water and chilled water. You can search for energyplus radiant to review other posts on this topic.

Your comment about cooling via convection (cooled air drops from the ceiling) is accurate in reality, but EnergyPlus is an energy simulation engine -- not a computational fluid dynamics (CFD) simulation engine. Understanding those airflow details would require using a tool like Ansys to perform such a simulation. If you are willing to do that, you could then use the CFD results for air temperature within the zone as an input to EnergyPlus using the Room Air Model that defines non-uniform temperature distribution of air in a zone. Without the room air model, EnergyPlus assumes that each zone is "well-mixed" and it's entire air volume is homogenous (at the same temperature & humidity).

For the air flow rate caused by convection cooling, that could be defined as a velocity schedule and applied to the People object assigned to that zone. This allows EnergyPlus to update the detailed thermal comfort outputs (PMV, PPD, etc.) for those occupants accordingly.

Other than that, EnergyPlus can also alter the calculation approach for convection coefficients on the interior side of surfaces. This can be done with one of the options of the SurfaceConvectionAlgorithm:Inside object or by applying your own convection coefficients using the SurfaceProperty:ConvectionCoefficients object. It sounds like you want to use the algorithm approach with the AdaptiveConvectionAlgorithm option, which should use the Karadag algorithm for in-ceiling cooling by default (see below from the Engineering Reference).

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You can also customize what algorithm is applied to different surface types using the SurfaceConvectionAlgorithm:Inside:AdaptiveModelSelections object.

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Thank you Aaron for your thorough and in-depth answer. This gives me quite some threads to follow already.

My comment about the "dropping" cool air was actually meant as a hint that I consider the air in this scenario to be mixed. As warm air has the tendency to rise and a cooling ceiling means the cooled air there has a tendency to drop, I assume a well mixed air in the room by inherent means (i.e. no forced ventilation). Contrary to what would happen (or rather: not happen) by a cooling floor. cheers.

blackbody's avatar blackbody  ( 2022-11-22 09:45:44 -0600 )edit

@blackbody you're welcome, and having the zone be mixed as a result of dropping cool air and rising warm air makes sense.

If you think that my answer was adequate, click on the green check mark to accept it and let others know the question is resolved.

Aaron Boranian's avatar Aaron Boranian  ( 2022-11-23 12:06:11 -0600 )edit

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Asked: 2022-11-22 03:13:33 -0600

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Last updated: Nov 24