The valve is allowed to control the temperature of the room because it measures the temperature locally to it and is very good at maintaining a stable temperature in the room. The reason for not letting the room sensor do this fine control and the minute-per-minute control of the temperature and plunger position on the valve is battery life. To maintain a steady temperature in a room the valve needs to measure the temperature every minute, and then adjust its valve position accordingly using TPI (temperature proportional integral) control. It does this by measuring the temperature of the water as well as the room temperature locally to it. If every time it had to do this it also needed to communicate with the room sensor to get that temperature, then the battery life of the valve and room sensor would be seriously depleted, or the temperature fluctuations of the room would be considerably large if we reduced the temperature sample rate of the valve. For this reason with rooms with more than one radiator this is a very good thing and if one end of a large room is colder than the other then the valves will work independently to heat the cold end of the room but will throttle back the warm end of the room. However if the global temperature of the room were to over heat then both valves would be shut off and sent the temperature of 4º because the room sensor would pick up the global temperature for this room having gone above the target temperature.
The valves measure the temperature of the room and they have two temperature probes built into them. One which measures the temperature of the water (against the pin of the valve) and another temperature sensor behind the screen. This means that they are very good at interpreting the change in temperature in the room, as the valve recognises how it is being affected being next to a hot source. However we know we would be criticised if we reported this temperature to the app, as in some cases valves are behind large pieces of furniture or a heavy curtain for example. So we only report the temperature from the room sensor as this is placed at chest height in the room and is a much more accurate representation of the room temperature.
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