How to model GSHP with Radiant in Energy plus

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Yes, EnergyPlus does have a GroundHeatExchange:System object to define the ground loop heat exchanger. This requires other objects like a GroundHeatExchanger:Vertical:Properties object to define the heat exchanger geometry and performance as well as a GroundHeatExchanger:Vertical:Array object to define the layout of ground heat exchanger boreholes (there are other objects for different borehole or heat exchanger configurations).

Now that you know what EnergyPlus objects you are interested in using, search for those object class names "GroundHeatExchange:System", e.g.) in the ExampleFiles-ObjectsLink.html file that is in the ExampleFiles folder of your EnergyPlus installation. Most EnergyPlus example files have this heat exchanger serve the supply side of a condenser for a heat pump, but the GSHP-GLHE.idf example file has the heat exchanger as the condenser equipment for a chilled water loop. You could use this as a reference and replace the chilled water connections with radiant cooling system connections. Radiant cooling systems are defined by a low-temp variable flow option or low-temp constant flow option in EnergyPlus, both of which also have plenty of example files. Refer to this post for more details on radiant cooling system modeling and this post for finding and modifying example files that are useful.