MVHR control

I have a similar problem with my MVHR, but I do not have a "defrost valve" to control.
My problem ist that if the air humidity is too high and the outside temperature is below ~0°C the external intake filter will freeze over completely and no air at all is able to get through.

In advance: I use Home Assistant for "my solution"
I also used Shelly Mini's to "simple" control my MVHR by switching some external input triggers on/off. But now I use a Modbus TCP Ethernet-Adapter to get MANY datapoints and also control the MVHR through the included interface.

The default HA "device page" of my MVHR - there are tooooooooo many datapoints to use them all , but some are really useful.
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So I now have much more control over the available functionality of my MVHR and I also get several feedback-signals of the state of the MVHR.
=> I suggest you use a Modbus-Adapter too because it has many advantages
The MVHR itselfe will probably have the ability to control the valve!


Additional information how I try to "solve" the problem with my MVHR + ice - perhaps it helps you somehow with your whole implementation:
My Problem with ice: my system does not even have a defrosting functionality/valve - but it would not help in my case anyway:
I have the problem that the EXTERNAL intake filter (outside at the house wall) freezes over. There is an intake filter which seems to "accumulate" water and freezes completely over and then the MVHR does not get fresh air at all and "recycles" old air from somewhere inside - in this state there is no benefit to activate the MVHR at all and I wanted to disable the MVHR to at least save some power.

My "solution" for this problem:
v1) Because the simple "external temperature detection" is for my setup by fare not enough I tried to detect the difference of the temperature of my external weather station (Ecowitt Wittboy WS90) and the intake temperature of my MVHR - when the difference is >3°C (because the intake is blocked by ice and uses some internal WARM air as "intake") I shut down the MVHR completely until defrosting is "detected" (= by hand ).
The Problem is: the intake is already frozen over at this point

v2) I use the external humidity and temperature to calculate the "dewpoint temperature". If the external temperature is <= the external dewpoint temperature and the external temperature is < 0°C I shut down the MVHR BEFORE it freezes over.
=> This is still in the test phase

Example trace:
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Zitat von borsti0

But now I use a Modbus TCP Ethernet-Adapter

Which device/model do you use?

I use the Waveshare RS485 to RJ45 Ethernet Converter Module (~38€) as PoE-variant. There is basically no firmware support, software support and documentation from the manufacturer, but I was able to integrate it with Home Assistant anyway.
For "configuration" you must use the web interface or the software "Virtual Serial & Device Management" alias "VirCom".

Because I did not have ANY experience with Modbus and after several failed tests I also bought the Waveshare Industrial USB to RS485 Converter with original FT232RL 300-921600bps (~18€) to test to communicate from 1 device to the other using a Modbus slave and master software.

I used a combination of "qModMaster" and "Modbus Slave" to try out several modes, parameters, register datatypes, ...
After successful tests I also used the "Modbus Slave" software to try to access the registers of the simulated device with HA.
=> Only after these first tests I connected the RJ45 Modbus adapter to my MVHR.

My parameters of the Waveshare RS485 to RJ45 Ethernet Converter Module as "Gateway":
Attention: I increased the Baud Rate to 115200 baud => this parameter I had to change via my MVHR terminal, default was 9600 baud.
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Initially I mapped each register by hand in the yaml file, example with only 1x "binary_sensors":
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But I was lucky and found a Modbus integration directly for my MVHR-device and could remove these lines (and several more) - you have to read the Modbus help for HA to understand these and MUCH more available parameters.

borsti0 Thank you very much for your detailed explanation.

I have already looked at the Wavelink devices and consider them suitable. But it is always very helpful to hear about the real experiences of users.