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# Open Studio 1.5 Radiant Panel Surface Group Error

I am getting the following error while trying to model a low temp radiant system:

Program Version,EnergyPlus-Windows-64 8.1.0.009, YMD=2014.11.14 10:36,IDD_Version 8.1.0.009
** Severe  ** IP: IDF line~572 Object=ZONEHVAC:LOWTEMPERATURERADIANT:SURFACEGROUP, name=LOW TEMP RADIANT VAR FLOWCEILINGS, Required Field=[Surface 1 Name] was blank.
** Severe  ** IP: IDF line~572 Object=ZONEHVAC:LOWTEMPERATURERADIANT:SURFACEGROUP, name=LOW TEMP RADIANT VAR FLOWCEILINGS, Required Field=[Flow Fraction for Surface 1] was blank.
** Warning ** IP: Note -- Some missing fields have been filled with defaults. See the audit output file for details.


The idf looks like this:

ZoneHVAC:LowTemperatureRadiant:SurfaceGroup,
Low Temp Radiant Var FlowCeilings;      !- Name


and nothing else follows after this, so the surface names and flow fractions are missing (below is cut and pasted from EP input output ref):

ZoneHVAC:LowTemperatureRadiant:SurfaceGroup,
Zone 1 Radiant Surfaces, !- name of surface list
Zn001:Flr001,            !- Surface name 1
0.75,                    !- Flow fraction for surface 1
Zn001:Roof001,           !- Surface name 2
0.25;                    !- Flow fraction for surface 2

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I am not sure how this works in OpenStudio but we model radiant ceilings a lot in EnergyPlus (the background engine). In EnergyPlus you need to name the ceilings which are radiant, they have a special construction called construction:InternalSource. These radiant ceiling surfaces need to be put into a surface group (ZoneHVAC:LowTemperatureRadiant:SurfaceGroup, if you have more than one surface per zone that is a chilled ceiling. In the surface group EnergyPlus asks that you specify the surface name of your chilled ceiling and the percentage or fraction that each surface takes of the overall area in the zone that is chilled ceiling. So if you have two chilled ceilings which have an area of 20m² and 30m² respectively then the fraction for the first is 0.4 and for the second 0.6, all fractions must add exactly to 1 for each surface group.

This surface is then put into the radiant ceiling object, ZoneHVAC:LowTemperatureRadiant:VariableFlow. If there is only one chilled ceiling in your zone you can just put the surface name in there.

If you have pulled the idf out and opened it in E+ then these are the two places to look to check for these things: ZoneHVAC:LowTemperatureRadiant:SurfaceGroup ZoneHVAC:LowTemperatureRadiant:VariableFlow

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@Annie Marston is correct. You need to:

1. Specify which type of surfaces are set to be the heating/cooling surfaces (in the ZoneHVACLowTempRadiant object).
2. Make sure that the type of surface you have selected has an InternalSourceConstruction assigned to it.

On translation to EnergyPlus, OpenStudio will assign all surfaces of the selected type in a zone with low temp radiant that also have an internal source construction to the ZoneHVAC:LowTemperatureRadiant:SurfaceGroup.

( 2014-11-14 16:17:08 -0600 )edit

Thanks, and where do I get this InternalSourceConstruction from? There is a category for this in the library but no constructions within it, nor when I search the BCL.

( 2014-11-17 07:40:04 -0600 )edit

You can create this yourself. It is similar to how you would create a construction, so layer your materials one by one, then you either need two layers of concrete, if you are modelling active slabs, or an air gap and a metal layer (or similar) if you are modelling active ceilings. There are a few more inputs into the internal source construction and those are best explained by the input output reference guide that comes with EnergyPlus (i am sure you can google it to come up too). This is without a doubt the best source of help there is.

( 2014-11-17 08:03:50 -0600 )edit