Gas central heating HVAC system loop Open Studio

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Hello to all, I created a building with several thermal zones working with Sketch Up and Open studio. Using "Ideal loads" my simulation works - so far, so good. However, the simulated sensible heating energy is much too low. Thats why I would like to simulate the actual heating system, but as simple as possible. The building actually has gas central heating. That means, in a large tank in the basement water is heated with gas and in each room there is a water-based radiator for heating. In Open studio I chose unter thermal zones-->HVAC systems-->zone equipment--> low temperature radiant variable flow. In addition I added under thermal zones--> heating thermostat schedule my custom schedule. Now I have to create the suitable air loop and there are several points confusing me. What the air loop MUST contain? In the library I found under coil heating water-->HW Heating coil which seems to be necessary at the supply equipment sideI already found out, that I also need a setpoint manager at this side. On the demand equipment side there should be my thermal zone(s). Now to my questions:

1. All my thermal zones will have the same heating schedule and setpoint temperature and belong all to the central heating system. Am I correct in thinking that I can put all thermal zones in one air loop and switch them in parallel?

2. Do I need another plant loop for my HW Heating coil which contains the gas heating, maybe using the gas heating coil? Or can the gas heating coil be directly in the air loop before the HW heating coil?

Thanks for any help! Maria