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# Gas central heating HVAC system loop Open Studio

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

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The ZoneHVAC:LowTemperatureRadiant:VariableFlow object represents a radiant heating system where water is used to supply/remove energy to/from a building surface (e.g. radiant concrete slab or radiant ceiling panels). To model a typical hydronic radiator I would suggest using ZoneHVAC:Baseboard:Convective:Water.

As far as the air loop, you don't necessarily need an air loop if the zones are only conditioned by hydronic radiators and there are no ventilation requirements. But to answer your question, yes, you can serve all of the zones with a single multi-zone air handler, which can either utilize a water heating coil (from either the same boiler plant serving the baseboards, or a different boiler plant) or a standalone gas furnace (Coil:Heating:Fuel).

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Hello Eric, thanks for helping me. I used the baseboard:convective:water and the plant loop "service hot water" which is the only predefined plant loop in OpenStudio. Can I use the preset water:heater:mixed also for heating the baseboard:convective:water?

( 2021-12-13 06:45:39 -0600 )edit

Water heaters / service hot water loops are intended for domestic hot water, not heating hot water. While it is possible that you could get the baseboard system to "work" using a water heater, a more realistic system would be served by a boiler instead of a water heater.

( 2021-12-13 10:18:15 -0600 )edit