Uneven Heating in over_climate mode with 2 TRVZB

[fatSquirrel42]

Hello,
Versatile Thermostat works very well for me, except in one room. It is the largest room in my apartment, measuring approximately 9m x 4m. There are two radiators in the room, one at each end. One is a “normal” horizontal radiator. The second is relatively narrow but very tall.
I have a Sonoff SNZB-02P in the room, which is used for the room temperature for the VTherm. It is located in the middle of the room between the two radiators. There is a Sonoff TRVZB on each of the radiators. The room is set up as an over_climate VTherm, in which the 1 temperature sensor and the 2 TRVs are registered.
My problem is that one radiator is always significantly warmer than the other at the same valve_opening_degree. As a result, one end of the room is always very warm and the other cool, because Versatile Thermostat tries to reach 21 degrees on the SNZB-02P.

Does anyone have any suggestions on how I can solve this problem? Is it perhaps possible to set an offset between several valve_opening_degree?

[caiusseverus]

I think in this case controlling both radiators by the same VTherm may not be the right solution. The radiators are in the same room, however their size difference means that the power output is not going to respond the same - 50% output of the large one will result in a much larger heat output than 50% on the small one so that will result in the temperature gradient you are seeing.

There is no facility to control the two radiators differently within one VTherm, other than the maximum closing degree which holds the valve open. That probably won't give you what you want.

I think you may have to set up one VTherm for each radiator, albeit using the same temperature sensor. You can then use more aggressive tpi coefficients on the smaller one to make it give higher output for a given temperature.

This is one example where the added complexity of external control makes things difficult - with normal TRVs you would just set them both to a temperature and they would automatically regulate their output without any issue, albeit less precisely.