I have been wondering about a solution to this for long so I've decided to ask it here. I'm a programmer, not an electrician but I know how to properly solder things and generally how to work safely with electricity and test voltage, current, amps accordingly. In my home I have a "heat recovery installation", some mechanical ventilation unit that basically ventilates the house with fresh air while removing dirty air and retaining the heat. Warnings that 240v is lethal are welcome, but I am fully aware of that. I suggest anyone not comfortable working safely with electricity not to do any of this and search for a professional electrician.
That unit I have is connected to a wall outlet in a non-standard perilex configuration. As far as I know perilex was supposed to be only used for 380v but apparently the manufacturer decided to use it in a non-standard way for switching a 240v line over three channels. Probably something like this:
I want to be able to control this device in a non-invasive way. Meaning, I rather don't open the unit and play around with the low-voltage controllers inside. I want to make a simple box that I connect in between the wall outlet and device that allows me to make it smart and switch over my wifi network between the three modes while also keeping the ability to override it with the current physical switch.
I want to make use of as much standard parts as possible and using a raspberry pi. I found a low-voltage measurement unit that I suppose I can use when using any standard, approved, safe "240-5v usb adapter" in between. I came up with the following idea (image below, black rectangle), which involves a raspberry pi, some kind of low-voltage measurement unit and a 240v relay module. My idea is to make a box with a perilex connector that I plugin to the wall and on the other hand have a perilex socket that I connect the heat recovery unit to. I choose to convert 240v to 5v as early as possible to do the least possible with the higher 240 voltage, which is generally more safe. I would be also fine measuring 240v instead too but I didn't find such modules yet. I'm not even sure I need to do voltage measurement, maybe I can use some kind of relay module that I can physically set with the switch and than read the on/off status from. The general is to be able to set the relay status from my wifi network but if the physical switch is changing mode 1/2/3, to use that. I could easily program that once I have the "read physicial switch mode 1/2/3" and "set relay 1/2/3" functions.
This is just from the top of my head, but I have no idea if this is a good and safe way of doing it. I already have a raspberry pi I can use but I am still searching for the other specific parts, if someone has any idea's that would be welcome. I also need to be sure that only one of the three relays is on at the time as I am not sure how the unit will handle it when multiple relays are on. I can program that but, if another kind of physical "OR" switch is available, I rather use that.
So, I am searching for raspberry pi modules I can use in this case and some wiring schemes as I have no idea how to wire those to raspberry pi (yet). Is my general idea correct? How do I properly wire it? Is there anything I can do to make it safer (like with diodes) and protect my low-voltage modules/device better? Is there a way I can ground my raspberry pi and it's units? Or add an temperature sensors for overheating protection? Is there a standard unit or plug-and-play solution that fits my needs better? Also, I now used an additional plug for powering the relay and unit but I rather use the electricity from the original perilex plug, how do I wire this? Is the wiring from the second example sufficient for that?
Also, if there is some module or way I can use an overvoltage protection before my "240-5v" adapters, that would be also great. Or maybe I would just swap three of these in between:
Additionally: The HRV unit (with bypass) is from Brink Climate Systems, type Renovent HR 2/2 RBP Medium from the year 2007 with a max air flow capacity of 300m3/h. Rated power consumption is 45 watt at 230 V ~ 50 Hz. The English manual can be found from page 43 here: https://www.brinkclimatesystems.nl/documenten/renovent-hr-medium-large-611925.pdf.
It does seem to have an unused RJ12/6 and OpenTherm connection which can maybe be used too.
Below some additional photos as requested in the comments:
And the (redacted) label from the front of the unit: