'over_switch' Mode | How to setup VT for low temperature underfloor heating systems correctly?

[Linus86529]

Hello jmcollin78,

since this is my first time here, I first searched the existing discussion posts for a similar case, as recommended.

And I almost got lucky. Unfortunately, the discussion on “over_switch or over_climate? #924” only partially applies to my underfloor heating. Unfortunately, I can't find the answer to my questions there, or any tips I could follow.

Before I get to my question, I would like to add some additional information.

The water-based underfloor heating runs in “over_switch” mode, as described in the VT description:
'https://github.com/jmcollin78/versatile_thermostat/blob/main/documentation/en/over-switch.md#prerequisites'

The only and decisive difference between the description and my setup can be found at position 6.

Instead of the heater, I use a 230 V actuator (technical data: https://www.strawa.com/wp-content/uploads/2020/04/55-00507x_IS.pdf) that operates a valve. This allows warm water at a constant temperature of +40 °C to flow into the heating loops of the underfloor heating circuits – or not.

The actuator used has only two states: completely closed (0 volts) and completely open (230 volts).
It takes 180 seconds to move from completely closed to completely open.
The actuator therefore needs 360 seconds to complete the entire travel distance OFF → ON → OFF.

The actuator is also switched by a 230 V switch, as shown in the description.
In my setup, the switch is a “Wave 1 Mini” from Shelly for 230 V.

So what's my problem?

• 1.) Slow-moving valve actuators are installed in the control loops of the underfloor heating circuits (180s from OFF to ON or from ON to OFF).
• 2.) The flow temperature to the underfloor heating circuits is relatively low at a constant 40°C. - Advantage: low risk of overheating.
• 3.) In ‘over_switch’ mode, the ON-OFF interval is 300s (cycle_min: 5).
• 4.) The ON time is usually 60s for me.
• 5.) The OFF time is usually 240s for me.

Could it be that the VT is optimized for electric radiators with an output in the range of several kW in the “over_switch” operating mode?

What settings would need to be made in Versatile Thermostat so that the switch (Shelly) could remain permanently in the ON position, as it is the case in boost mode, for example? This would allow the target temperature to be reached in a shorter time.

Due to the low flow temperature, it would certainly not be necessary to have so many ON-OFF cycles as for a high temperature heating unit.

Finally, here are two images.

• The first image shows the progression while the underfloor heating was set to “Boost” for a duration of 01:43:29.
• The green frame marks the ON time of 3,900 seconds. During this period, the actuator had fully opened the valve. So far, so good.
• The red frame marks a sequence of ON-OFF sequences in which the valve could never be fully opened, if that was the intention.

• In the second image, it takes three hours to bring the temperature back to the setpoint using 36 ON-OFF intervals.

[jmcollin78]

Hello, for underfloor heating with a very long inertia, you should set the cycle to a large value (15 min or 30 min) and have a minimum activation delay like 5 min. This is explain here: https://github.com/jmcollin78/versatile_thermostat/blob/main/documentation/en/tuning-examples.md#central-heating-gas-or-oil-heating

Then VTherm will avoid to switch on/off too often and don't touch the valve for less than 5 minutes. Of course you can adjust this values to your case.

[Linus86529]

Hello @jmcollin78, thank you for your prompt reply.

Oh my god! I recall this brief section on central heating appliances for oil and gas.

About a year ago, I saw this section quite by chance when I was trying out your ingenious VT HA integration for my seven DECT radiator thermostats. All seven have been running perfectly in ‘over_climate’ ever since.

At the time, I read the lines, but I wasn't at all sure whether I would ever need these values and might have to change them.
When I integrated the first underfloor heating into VT last week, I unfortunately didn't remember this information.

Please excuse me for being a bit stupid and ‘stealing’ your valuable time.
Thank you very much for your valued help and this wonderful integration.

Kind Regards

[Linus86529]

Hello @jmcollin78, it's me again.

I followed your advice and set the value to 30 minutes max right away, (cycle_min: 30). And I was surprised by the result.

Even when the room temperature matches the target temperature, in my case 20.0 °C, the value of “power_percent” is not zero.
And the valve continues to open and close within the 30 minutes cycle.

• The sensor 'sensor.fht_kuche_schalter1_power_percent' is at 7%.
• The ON-time is at 126s (~2 minutes)
• The OFF-Time is at 1674s (~ 28 minutes)

I expected that once the target temperature was reached, the valve would stop operating completely.
And that the valve would only start operating again when the room temperature dropped below the target temperature by a certain amount.

Is there still an error in my configuration?

[Linus86529]

After reading this information here and here, then changing some parameters (highlighted) in the “TPI attributes” configuration accordingly, I will see if it meets my expectations.