Integrating HVAC system to HA via BMS interface


so here’s my problem: I have a Vent-Axia Sentinel mechanical heat recovery system installed in my house. It has some level of autonomous automation built in but otherwise it’s manual and I would love to have some more control over it and get more data from it.

Going through the manual, I found it has a BMS (building management system) interface connector.
After some googling, my understanding is that the BMS interface is there so that the system can be optionally hooked up to some centralized digital system.

Following that thinking, I’m wondering if I can somehow use the BMS interface to get data from (and possibly to) the MHRV box and get it to talk with my HA. Is that possible? Have anyone tried this before?


What protocol does it use? BACnet, 1-Wire, modbus, modbus +, etc?

That’s exactly one of my problems that I don’t know but since BMS is some kind of an industry-wide standard, it surely must be using a standard protocol. I googled BMS but the information I found is pretty generic mostly mentioning BACnet but nothing specific about Vent-axia systems. I was just hoping that somebody here already might have had some experience in using BMS to integrate some hardware into their HA.

No standard that I’m aware of. I work in the HVAC/R industry and E/BMS systems can utilize any number of protocols, even within the same product lines.

Perhaps contacting the manufacturer of the product will help?

Ok, thanks for that, I will get in touch with the manufacturer and will come back here with what they said.

I’m glad I found this tread! I also have a Sentinel Kinetic MVHR installed and this has been on my list for a while. Just looking back at the manual and I too just found the bit about the BMS which I was otherwise not aware of. Please keep this tread up-to-date with what you find out from Vent Axia.

Just looking at the installation and servicing manual and on page 20, I see the wiring diagram which shows the BMS slot. If the BMS does not work out, wondering if we are able to do something in ESPHome to control it that way? I am new to ESPHome so we would definitely need more help.

(Not my photograph: Taken from here)


only yesterday I got a good amount of info from Vent Axia, I think you will like it :smiley:

First of all their reply was this: “The BMS port was never really developed and doesn’t offer a lot of control but please find the attached information. Its only function really is to enable to system.”

I got two pretty useful documents from them but TBH I’m not sure how I can attach them here so I put them in my dropbox instead:

Using the info contained in these two docs my initial plan is to:

  • sense 5v signal on the “fault LED” output
  • connect across terminals for a remote boost function

I would also love to have it connected via HA to my fire alarm so that I can stop the fan if the fire alarm activates. Unfortunately, that won’t be so easy. Using ASCII commands sent over RS232 to only just start and stop the unit is serious overkill :slight_smile: I might do it in the future but it seems like a lot of work.

Finally I’m going to try to control the unit RPM using the proportional voltage 0-10V. That should be easy, as long as I will manage to find some DAC converter that will be able to give me that 0-10V and will connect to HA somehow. Any advice would be appreciated here.

All the best with your integration and keep us updated here, I will do the same :+1:

It appears for basic mode 2 functionality, you should be able to do this with ESPHome and some dry contacts

S/W’s 1-3 should give you mode functionality.
S/W 5 should give you fire / all stop functionality.

One thing that is not clear to me is what “With link Fitted to J4” means??

My picture actually shows J4 jumper. In my own unit pins 3 and 4 are shortened with a jumper. I believe that jumper can be removed and some kind of room humidity sensors can be connected to this 4 pin connector? Only a guess.

Excellent! Thanks for sharing. This is looking positive and keen to get going. Although, I am a slight novice and not really worked with ESP Home / electronics (apart from flashing smart plugs)… but will follow your lead and let me know if I can help anywhere.

Just so I am following, you think it is possible to be able to control the unit via HA and for the unit to also report its current status (I.E running in boost mode etc)?

This is also super!! I’m really excited about this now. So I understand, I think you are saying that this can be controlled with an ESP(8266) type chip and connect some of the wires to the connections. For example, I assume that when a ‘signal’ or an electric pulse is sent and received via say for example S/W1 - the unit will go in ‘Low Mode’ ? Can it report data to the ESP chip?

My understanding is that you cannot get any data from the unit, unfortunately. All we can do is install ESP or a similar controller with a couple of small solid-state relays connected to the Sentinel SW inputs. I actually think I will go with Shelly Plus I4 instead of ESP as it’s much easier and most of my house is already running on Shelly. If the SW connectors have common ground, then I shouldn’t even need any relays.

I was wrong about the Shelly I4 - it’s a sensor rather then a relay. Back to ESP.

Something like this maybe: 4CH WiFi Switch Tuya Smart Life Remote Control Wireless Smart Switch Modul DIY 4 Gang Relay Voice Control with Alexa Google Home|Home Automation Modules| - AliExpress

The way I read the litt:
in mode 02, switches 1 through 3 can provide control for LOW - NORMAL - BOOST Modes. The assumption is on what J4 pins need to be shunted?

So shunting switch 1-3 (in mode 02) should provide manual override for the respective mode.

Switch 5 will provide all STOP for fire, so this would need be connected to normally closed contacts in mode 02.

I’m thinking you should be able to test this without any hardware. Move unit into mode 02, shunt SW 5.
Make sure unit operates as normal, then once confirmed operation jump SW-3. That should force the unit into ‘boost mode’.

If the test works, then you should be able to use any device (Z-Wave- Wifi - Zigbee, etc) that incorporates dry contacts.

I just tried it and I don’t understand the results.

I powered the unit down (unplugged from mains), powered back on, on the startup sequence I have change control mode from 01 to 02. After the unit finished initializing, the fan remained off and the screen said: Control mode: fan off".

Pressing buttons, combination of buttons or pressing and holding them did not do anything. Shortening SW1 or SW2 or SW3 did not have any effect.

I did not touch J4, I left it with pins 3 and 4 shunted.

Did you shunt SW5 ? As I read the manual, in control mode 02, you must shunt SW5

Ok, that was my fault yesterday. In a rush I forgot about that SW5. After some testing just now I can confirm that:

  • After shunting SW5 and powering up the unit, it started in automatic airflow (I have internal humidity sensor fitted)

  • shunting SW1 to SW3 forces the Low, Normal and Boost modes accordingly for as long as it’s shunted and then it goes back to automatic mode

  • not sure about SW4. Shunting it also put the unit in boost mode but it did not go back to Auto, instead it remained in Manual and I had to power cycle the unit to get it to work in auto again. I have to refer to the manual again but right now I hardly found a time to do this testing abd write a post in between work, other diy and kids baths, dinner and bedtime :wink:

So far I’m delighted with the results as it looks like integration with HA will be easier than I thought.

I found it and it all makes sense now:

Fantastic, so for now you’ll have fire (all stop) control and mode control. Now how to get some sensor feedback from the unit… Hmmmmm

Since the input sensors are simple analog devices (return voltage; 0vdc = Off (0%) and 10vdc = On (100%)) you might be able to use an ESPHome to monitor the sense voltage from the inboard sensors (assuming you can get to the common and sense pins).

With that information you could map it’s value in HA.

Good idea. I just don’t know if I will have time to go that far but I might :wink:

I’ll be hunting for a 4 channel wifi relay this weekend.

Thanks a lot for all your help and hopefully more people will find this thread useful.

Next on my list will sensing signal from fire alarms but that should be easy es they are all hardwired and interconnected.


Please keep us updated on your equipment, setup and how to integrate. I’m not confident to try yet myself but I’m eagerly watching from a distance.