I have recently purchase a Vent Axia PoziDry positive input ventilation system which is pretty much a ‘commission it and leave it’ system that doesn’t require too much interaction, except where you want to boost the output of the fan.
Vent Axia provide a remote control functionality for this which pretty much just amounts to a 15 metre cable with a 4-pin JST connector at the fan unit and a dumb toggle switch that makes or breaks the circuit:
The rub is that you can only purchase this part directly from Vent Axia and it’s over £100 for a length of cable and a toggle switch. It also offers no ability to integrate it with any other system.
So here’s my thinking, the 4 pin connector and enough flex cable to run from the loft to the nearest accessible location is significantly cheaper, but I need some way of closing the circuit via Home Assistant when I want to activate boost mode based on an automation of the average humidity in the house.
I’m probably overthinking this, but I just need a simple low-voltage relay to make/break the circuit, is that right?
Could a Shelly Plus 1 or something similar to this Zigbee relay work?
I have been looking at the Pozidri systems and was thinking exactly the same thing about the boost connector.
Any relay with volt-free contacts ought to be OK. Shelly plus 1 or shelly plus 1 mini was what I was looking at but the ZigBee one you link to looks fine to me as well.
From what I can tell they use JST-GH 4 pin connectors, but I couldn’t find any that didn’t have a 4 week delivery lead time to the UK.
What I ended up doing was to hack together my own connector using three dupont pins as per below (not the best photo, so I outlined the layout of the pins):
I then soldered them to a length of 0.75mm2 two-core flex. I wanted to be absolutely certain that no voltage could be passed back to the PIV (which passes 9.5v down to the volt-free contact), so the flex runs into a Salus SR600 volt free zigbee relay, designed for switching volt-free contacts on boilers. I managed to get one for less than £20 on a Black Friday discount.
As I need to include a manual override (for spousal acceptance factor) I’ve connected a standard toggle light switch onto the S1/S2 contacts of the relay. I’ve made a change locally to Z2M to allow setting the S1/S2 contacts - which needs to be done via a parameter change. I haven’t had chance to create a PR to get it merged into a release as yet, but it’s documented on this gist.
This setup works really well, enabling us to switch between boost modes locally and remotely and enables the triggering of automations based on factors like humidity, cooking, and VOC levels.
The main PIV unit itself is wired into a Scolmore ClickSmart+ Zigbee FCU So I can control power to the unit remotely if need be, and use the switch status and other factors (like temperature in the loft) to work out the energy consumption using PowerCalc.
