Heat pump monitoring pre-provisioning etc

Hello, I’m working out what exactly to order to monitor my 5 kW Arotherm. I already have a Sontex 789 installed, but don’t have any OEM kit so far. Is pre-provisioning still possible if you don’t have the Sontex in hand?

Is it possible to add further temperature sensors to the emonHP? This is not critical but I’d like to add an indoor temp if possible.

Last question, I am thinking of using only a single SDM120 electricity meter to monitor birth the heat pump and the controls (on the same circuit I believe) with CT clamps measuring the immersion heater. I haven’t been able to find much info on what the accuracy penalty is likely to be, but I think not very much for a resistive load?

Thanks very much!

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Hi Fiona

I’ve got the following.

Sharky 775 (equiv of your Sontex)

Raspberry Pi 3 with heat pump hat on top (MBUS & Temperature RaspberryPi HAT | Heatpump Monitoring - Shop | OpenEnergyMonitor)

The hat allows mbus connectivity to the heat meter as well as 4 DS18B20 temp sensors, so use one of these outside temp? Possibly indoor temp if you can run a cable to the right place?

Also plugged into the Pi, i’ve got the modbus USB adaptor that talks directly to the SDM120.

I’ve also got separate CT clamps (via emonTX/emonPi) monitoring the immersion. But really, my plan is to go HOT water (55+) and not really have to worry about legionella immersion cycles.

For indoor temp, it’s a bit cumbersome, but i’ve got zigbee temp sensor feeding into Home Assistant and them passing onto emoncms.

Does that help?
Any questions let me know.


Hello @frh, we can definitely help with the provisioning, doesn’t need pre-provisioning, just makes things easier. The heat pump HAT on a Pi as @Zarch has is a good configuration if you want additional temperature sensors. Do you have a spare Pi already or will you need a new one? Did you already have an emonPi or emonTx?

Buying a CT monitor just to do the immersion is more expensive than just getting a second SDM120, but if you want to monitor other circuits it may well end up cheaper.

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Thanks @TrystanLea and @Zarch. I’m starting from scratch (apart from Sontex heat meter) and really not sure what I need!

Is the heat pump monitoring kit self sufficient or would I also need an EmonTx/EmonPi? If it’s just the immersion CT clamp and temp sensors adding complications then I could forgo those and stick with the second SDM120 meter and external temp from the internet. And Internal temp should be mostly constant.

The raspberry pi with the heat pump hat looks like a good setup, but the heat pump bundle has the advantage of being in stock. :slight_smile: Thanks again!

Hello @frh

Yes it is self sufficient, no additional EmonTx/EmonPi needed as long as you dont need CT sensors.
The heat pump bundle without the heat meter but with 2x SDM120 meters and the MBUS reader (included) is best if you want the simplest solution, with our help with provisioning and setup remotely - that’s part of the reason it’s more expensive as there’s a fair bit of our time included.

One downside is that there is no wired temperature sensor option with that bundle for additional temperature sensors (beyond the flow and return temperature sensors provided by the MBUS heat meter itself).

If your keen for the heat pump HAT option with a couple of additional wired temperature sensors I could put together a custom bundle for you. We don’t have a nice enclosure for that as it’s usually more of a DIY approach but we can do the rest of the setup for you if that’s useful. How much would you like to get involved with the configuration side of things?

I’ve put another 4x of the HAT’s in stock (the stock count wasn’t right on that one): MBUS & Temperature RaspberryPi HAT | Heatpump Monitoring - Shop | OpenEnergyMonitor
that needs a Pi running emonSD, Modbus reader & SDM120’s to make a complete solution. We dont sell Pi’s individually but I can make a custom bundle for you. I will PM you a few more details.

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Thanks @TrystanLea very kind of you to offer a custom bundle. In the end I think the emonHP will be the right thing for me at this point. I want to keep things pretty simple (not much time for DIY on mat leave!) and get a monitor on the heat pump this winter. Other adventures in monitoring will have to wait for another year or so. I’ll order the emonHP later today. :slightly_smiling_face:

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Hi @Zarch and @TrystanLea, a further question on placement of the electricity meters. Is there much value in measuring the indoor and outdoor units separately if it’s possible to measure them together? It would in theory be interesting to know the power used by the controls and the pump separate from the monobloc, but in practice not sure if that’s actually useful. Also curious what @johncantor thinks on this?

Hopefully I’ll get the electricity meters installed in the next couple of weeks and get going. Thanks for all your help!

I’ve done this Fiona.

I put a CT clamp on only the controller feed.
I’m not seeing a great deal to be honest.
The controller pulls 1W most of the time and around 15W during hot water runs when it kicks in the external pump on the water cylinder.

So likely less than 100W all day on my setup.

But I do include the controller on my overall ASHP usage.
The separate CT clamp on the controller just allows me to count that separately.

The loads might be split different on other models, but i’m not seeing a great deal on my Arotherm

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It depends on the heat pump, some heat pump controllers can use quite a bit of power. It’s definitely worth monitoring the power used by both the outdoor unit and indoor controller + pumps. Usually this requires two meters since often the indoor and outdoor units are on separate circuits. However, if they’re on a single circuit e.g EcoDan then it would be fine to monitor everything all together.

Since installing a few months ago my Samsung outdoor unit has used 222kWh while the indoor controller (+single primary pump) has used 25kWh, so about 11% of total consumption. My controller uses 5W on standby and 30W when running which is mostly the pump power. Some heat pumps have the primary pump located inside the outdoor unit (e.g Vaillant), therefore the power for this will be included with the outdoor unit.

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I guess its slightly unusual situation that the circ pumps and control has a separate supply to the compressor and fan. There can be a slight benefit having them separate if you are drilling into circ pump operation, however, mostly, all together will do. I have before put both cables through one CT. This does seem to work, and gives the total power of the 2. If you do have 2x CT, you can add them up on emoncms


Thanks all, much appreciated.