how to model a heating plate with constant temperature inside a building

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Hi there. For scholar purpose I would like to model a heating or cooling plate maintained to a constant temperature inside a building. Let say this plate is on a table inside a simple cubic building

I want this plate to exchange heat by convection with the thermal Zone (natural convection, no fan). The convective flux should be : $h_c(T_{zone} - T_{plate})S$. I would like to specify this in energyPlus. Specially I would like to be able ton provide the $h_c$ convective heat transfer coefficient.

How can I model this ? Reading the documentation I've seen nothing to set up a "surface" or "object" at constant temperature. Do I've to pass by an HVAC loop plant system ? Do I have to model my plate as a "floating surface" inside my building with my geometry preprocessor (then beeing not attached to any other wall ?)

In which type of object can I provide heat exchange coefficient ? I've learned about Internal mass and internal gain but I'm not sure this is good.

Thanks a lot.