Does a bit of condensation matter so long as it gets to dry out again fairly promptly? I.e., if there's some condensation when somebody has a shower but the MVHR doesn't go to boost but the trickle ventilation results in it going within an hour or so anyway, is that a problem? Would Gotanewlife's MVHR actually be working quite well without nudging? I suspect so.

Plenty of condensation in the bathroom here when I have a morning shower but it's gone by the time I've had breakfast.

Posted By: RingiYou have just admitted that your control system does not work, we can't expect "normal people" to nudge control settings.....

Weeeell, then neither does yours (one could argue) as you have to change yours twice a year; I change mine maybe 8 times a year but then I get 4 seasons . Also I haven't even had it for 6 months yet and as Ed alluded to (I think) it does seem like I don't need to use such fine adjustments especially as I am now increasing the hysteresis. It certainly IS a solution since it works for me! and I expect a majority of the MVHR using population could cope with it whereas only a tiny, tiny number would find a bespoke Rasberry PI controller manageable or perhaps no-one will if this thread is anything to go by. What is not a solution is a tiny pot, buried under an access panel, that can only set the RH to a target level plus or minus 10% RH.

Ref the condensation/mould thing and buffering, the more I think about it the more I think my particular en-suite is vulnerable due to the wonderful paint effect we stupidly went for, basically a plastic/vinyl coating, which covers the existing 3-5 cms of high breath-ability lime rich, weak, internal render......durrrrrr

Posted By: GotanewlifeWeeeell, then neither does yours

By control system works very well, just press a button outside of the bathroom if there is condensation! (To give a 10 minutes boost) Or do nothing and let it sort itself out over the next few hours.

Another update on a RPI controlling an MVHR unit - the good news is that I've successfully talked to the MVHR via the serial interface. The problem was with the non-RS232 standard signal voltage levels outputted by the RPi - the level shifter I used deals with the different system voltages but doesn't provide the uplift in signalling voltages. In the end, I used an old W2k pc and sent the ASCII commands, via a Comm port, in a text file using HyperTerminal - just as a quick work-around to establish that communication is possible. Using a MAX3232 chip and charge-pump capacitors (as Ed Davies has already recommended), it wouldn't be difficult to now get things working using the RPi. Comms is via 'proper' RS232 using a standard 9600 8N1 setup.

In the end, vent-axia provided useful support (I had tried them a couple of years back and they didn't seem interested, but they were prompt and useful this time). The less good news is they say the unit would need software revision to enable anything other than stop/start commands via the BMS interface (they would be willing to do that only if a big enough project came along). However, in saying that vent-axia have been helpful, that was up to a point - there's no response to a question about signalling and the wired remote (which is perhaps understandable).

For now then, on my set up, the RPi will control the MVHR just via the volt-free switches and the proportional inputs, i.e. switch the unit into low/medium/boost and control fan speed for normal and boost (within limits) - still very useful, but not 'full' control.

Of course, the option of buying a wired remote, looking at what's going on with an oscilloscope and then 'emulating' the wired remote is still a possibility in the future. In the meantime, it could be the case that the wired remote (which connects to the unit using the same BMS socket I've used) simply acts as an extension of the buttons on the unit's control panel. If anyone has any suggestions as to how to 'emulate' button pressing (ASCII commands seems unlikely?), I'm happy to try things out while I've got the unit rigged up to a pc.