PID control?

jonander

Hello,

I decided to purchase TADO for my home thinking it will be a perfect system to control my heating at home as I was told TADO uses a PID control algorithm.

First of all, I'd like to say that my building uses a central heating system, but each apartment can control the heating individually. This is because each apartment thermostat controls (using a relay output) a SIEMENS STA23/00 valve which lets the water flow into the radiators.

It takes the valve some time to fully open and close: 3 minutes approx from fully closed to fully open position, and around 10 minutes from fully open to fully closed position. Therefore, the thermostat shall start modulating the relay output (using kind of a PWM signal) long before reaching the temperature set point. In other words, you should use a PID control or you will always overshoot the set point.

The previous figure is taken from the SIEMENS actuator data sheet that you can find here (https://hit.sbt.siemens.com/RWD/app.aspx?RC=HQEU&lang=en&MODULE=Catalog&ACTION=ShowProduct&KEY=S55174-A110)

Point is that, it seems that TADO is unable to manage this properly, because it is always overshooting, so I don't understand how the PID control works in TADO thermostat. Anyone is having this kind of problems with a similar system? Will Tado learn about the system reaction times so that it can adapt the control algorithm? TADO support has confirmed that they are using a PID algorithm and it is fully compatible with my system, but I am starting to consider that it is not.

To make things worse, a couple of days ago TADO started to keep demanding heat even after reaching the set point.

How is this possible? As far as I know, even a wrongly adjusted PID algorithm will not demand heat once the set point is reached.

Thanks for your help.

Regards

Johanaza

Hi dear,
Did you find your answer, I have the same question.

Hunter

The wavy lines are confusing, often a single or even double wavy line is seen with no boiler activation. For me that means no additional heat input, so I guess that the single line is not opening your valve and the overshoot is a PID overshoot due to your radiator residual heat. The horizontal line that could be interpreted as a valve closure could just be graphing artefact. The whole wavy thing adds little and I am not sure even if it’s as simple as 3 lines is boiler on, I think it may be more complex and more to do with boiler timing bursts. I see this level of overshoot at first start up when the system was cold, looks normal ish.

Alternatively the valve opening algorithm may be firing to give a purposeful overshoot to limit boiler firing periods, that may be tuneable from support.