Reduce expansions tank "delta" - Control radiator valve change speed or spread open over time


Living in the Nordic countries it's quite common (due to regulation on energy consumption for households) that you end up with some type of heat pump, to power your radiators.

Many of these comes with an expansion tank as the "interface" between the pump and the pipes in your house, and is used for regulating the ups and downs in the circulated amount of water, combined with a circulation pump pushing the newly heated water from the heating system out to the radiators.

One issue when using the Tado smart radiator valves is that when schedules kicks in there quite the risk that all or most of the valves actively open or close at roughly the same time, causing the amount of water flowing through the pipes to change quite much in a short amount of time, i.e. the flow "delta" is huge.

The effect noticeable by this is that the expansion tank overflows, letting some of the water escape out the drain, but once the flow then changes it may end up with a too low water pressure/level to effectively flow the heating through the house.

Two possible suggestions I have for this is:

  • Make it possible to control the speed over which the radiator valves open/close. With the "traditional valves" I guess it's not a digital on/off (or 4-step as I believe the Tado valves provides) but a continuous state change from open to closed, smoothed by the temperature change itself. Making the valves open slower would mean less of flow change over a small amount of time, reducing the need for the expansion tank to vent.
  • Give an option to detect whenever there are many valves changing state at the same time, and allow to spread these open/close activations over a period of time instead. This would be extra useful in a combined room with multiple radiators, with individual feeds and valves, controlled by one temperature sensor.

As it stands now, I need to at least during the months where heating is toggled more frequently (spring and autumn) check the pressure in the heating system/expansion tank on a weekly basis. With one or both of above mentioned fixes it would reduce the risk of the expansion tank running empty meaning no heat can be transferred to the radiators any more.

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