Model Radiant Panels with DesignBuilder then with EnergyPlus

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Hi I model these systems all the time. here is what you have to do...

1. assign internal source construction to your ceilings where you will have the radiant panels
2. put all the ceilings you have in the surface group object for one zone
3. Fill out the ZoneHVAC:LowTempratureRadiant:VariableFLow, you might not have created these nodes previously so you will need to identify the hot water and cold water nodes with your own unique names
4. put your ZoneHVAC:LowTempratureRadiant:VariableFLow onto your equipment list for the zone
5. make sure your equipment connections are filled out for the zone, none of your nodes in ZoneHVAC:LowTempratureRadiant:VariableFLow will be in here
6. make two branches for your ZoneHVAC:LowTempratureRadiant:VariableFLow one for the cold side, and one for the hot side
7. add your branches into your branchlist for the demand side of your hot water loop, and the demand side of your chilled water loop
8. set up the boiler or district heating supply side of the loop (if you don't already have this)
9. set up the chiller supply side of the loop (if you don't already have this)

I do this in EnergyPlus and can help if you need more with this if you need more information.