Advice on OEM Level 3 Heat Pump Monitoring for Vaillant aroTHERM Split Plus

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Hello everyone,

In the upcoming months a local installer will add a Vaillant aroTHERM Split Plus VWL 75/8.2AS (R32, split system) to run in a hybrid setup with our existing Vaillant ecoTEC plus condensing combi boiler.

As a software developer whose already enthusiastically measuring everything electric and who has dozens of sensors broadcasting measurements via (ZigBee2)MQTT, I’ve asked the installer about the possibilities to install an OEM Level 3 Heat Pump Monitoring Bundle. He was willing to add the components after I confirmed it’s for monitoring only (not sending control commands to the heat pump). First hurdle cleared!

But since heating systems are not my field of expertise and also Dutch being my first language rather than English, I’ve got a few things I’d like some feedback on before potentially selecting the wrong components and giving wrong instructions to the installer.

Questions:

1. Primary pipework for the heat meter

OEM docs say: install the heat meter on primary pipework before any diverter valve, volumiser, or buffer.

My understanding:

  • Monoblock: primary pipework starts at outdoor unit => heat meter goes directly after outdoor unit.

  • Split system (my case): primary pipework starts at indoor unit => heat meter goes directly after indoor unit.

If so, the circuit (simplified) in my case should become:

Outdoor unit - (refrigerant line) - Indoor unit - Heat meter (prim. flow) - Heat distribution system - Temp sensor (prim. return) - Indoor unit - (refrigerant line) - Outdoor unit

Is this correct?

2. Heat meter selection

  • Sontex meters are often used when looking at the publicly shared configurations (glycol compatible, common in UK monoblocks).

  • For my split system, glycol compatibility seems unnecessary to me. AFAIK there’s no glycol mixture flowing through the radatiors, only water. Everything being indoors.

  • Would an Axioma DN20 (up to 10 kW) therefore be suitable?

  • Any tips on the pressure drop factor (a bit worried about this) and/or powering the meter (battery vs mains)?

3. Extra temperature sensors

The bundle contains the option for an indoor wireless temperature sensor.
I would like to add an indoor and an outsoor temperature sensor.

Can I add e.g. existing MQTT sensor data as a feed for this?

Or is it easier/more reliable to order two of these wireless temperature sensors, one for indoor usage and one for outdoor usage?

Thanks in advance for any advice!

Really appreciate the work behind OEM and all the documentation. Together with heating systems and heat pumps in general it’s a steep learning curve for a beginner, but very exciting.

Also, huge thanks to Heat Geek and Urban Plumbers for sparking my initial interest by showing what technically well-thought-out systems can achieve while also being aesthetically pleasing. OEM brings this full circle, tying back to my own field of expertise: fantastic! :blush:

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Welcome, Wil, to the OEM forum.

I’m sorry I can’t answer any of your Heatpump questions, but I can offer a comment about the emonTH, the battery-operated temperature and humidity sensor.

It is primarily designed as an indoor unit, so unless you put it in an enclosure that permits a free flow of air and protects against rain, driven snow etc, it’s unlikely to survive for too long outside. But, if you put one inside and close to an outside wall, you can connect a second temperature probe which is weatherproof, and run the cable through the wall. (And you’ll get inside and outside temperatures with just one emonTH.)

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Thank you very much for your insights regarding the temperature and humidity sensor. Really appreciate it.

I like the idea of running a cable through a wall as a fixed/static solution. :+1: