Gas central heating (water-based) with Group: Radiative/convective units

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Hello to all, I am trying to simulate a residential building which has a gas central heating (which means the radiators are water-based and the water is heated in a central gas condensing boiler). The radiators are classically mounted on the walls under the windows. Now I am unsure which of the Energy Plus options I should choose for the simulation. The group radiative/convective units contains among others 1. ZoneHVAC:HighTemperatureRadiant, which is according to InputOutputReference for electric or gas radiant heaters and not for hydronic radiant systems and therefore does not seem appropriate 2. ZoneHVAC:LowTemperatureRadiant:VariableFlow (or constant flow), which is accoring to InputOutputReference for hydronic radiant systems and therefore looks like the right choice. But then I wonder how gas consumption is calculated for this water-based heating system. Furthermore, at least in OpenStudio I can only choose ceilings and/or floors as radiant surface type (why?).

My questions: Is (2.) ZoneHVAC:LowTemperatureRadiant:VariableFlow generally first the right choice for my system? How/with which settings can I simulate the gas-consumption for heating? (Is there a way to do in OpenStudio?)

I have to say that the heating system is not supposed to be the focus of my simulations at all. It is actually only a necessary partial aspect. That's why I want to find a solution that is as simple as possible, even if it only provides a rough estimate.