Monitoring Energy Usage of heat pump (Heating and Hot water)

Hi there,

I have my mains power monitored with EmonPi and it is busy sending all it’s data to HomeAssistant which is working well. Ive have a Nibe F2040 and SMO20 installed away from my EmonPi kit and was wondering how to best monitor the energy usage for hot water and the heating circuit.

My consumer unit tells me the ASHP is on it’s own circuit.

The install looks complicated, and I’m wondering if anyone here could advise me where I might be able to attach the clamps of an EmonTX to send these values to HomeAssistant (via the EmonPi)

Here is an image of my ASHP hardware

Any help gratefully received!

Hi again, so i’ve not moved forward with this as unsure where I could add clamps to record energy usage for heating and hot water separately.

Does anyone know enough about installs of an ASHP to be able to advise?


I know nothing about heat pumps, so I’m groping in the dark here. What’s confusing me is you seem to be thinking that the heat pump will somehow have separate functions - one for heating and a second for hot water. I very much doubt that will be the case - I would think that the output of the heat exchanger is routed with valves rather than having what is in effect two heat pumps in the one enclosure, each with a separate electrical input.

Therefore, I think the only ways would be either to recognise the typical patterns of power input - and the snag there is nobody has yet managed to do this with any more than limited success, or to combine the electrical input with a knowledge of valve positions in order to deduce the separate energy usages.

Maybe @MyForest would be able to offer a comment?

Thanks, I’m not 100% sure either!

I can see, via HomaAssistant, when my heat pump is heating, I overlay my overall (household) energy use and can see a correlation, but I also see large spikes when the heat pump is not heating but instead working to improve the ‘heating top’ output value.

I’d like to be able to define the usage of each and have assumed that somewhere on that wall, there must be power source for heating, and a power source for hot water heater… Maybe incorrectly?

I’d think the hot water for the heating circuit, and the hot water for the shower etc are heated separately?

Thanks for the help! Hopefully can make some progress here

What I was getting at was the two might be heated separately but from the same source, and by knowing the valve positions you could allocate the electrical energy to the two functions. That’s a world away from using two c.t’s to measure two separate electrical inputs, which is what the plural “clamps” (you really mean c.t’s) and “values” in

seems to imply.

I see, that sounds more complex. Either way, I’d be happy to learn more about how to go about this!

Fascinating stuff

Hi @TheMiddle36uug

It may be that you and @Robert.Wall are just slightly missing each other as you are chatting.

Robert is indicating that you have a single heat pump and that it’s warm water goes to your hot water tank to heat the water in there, or it might go around your heating system to heat the house. I suspect that’s controlled by this valve which appears to have a black wire into your NIBE device on the left.


What you might be seeing is something Robert isn’t expecting, which is a top up from the mains electricity to boost your hot water even higher. Often that would be for an anti-legionella run, but it might also just be how your installer set up your heat pump. You’ve got a fused fused switches to the left of the broom handle that look like they might be the source of that power, especially this one because it has a thicker cable.


with mine, when it’s doing “resistive load” heating that wire would actually be warm to the touch. Which leads us to a trick…if you have a thermal camera it can show you where things are moving when you are interested.

Many of us in this forum like to keep the “domestic hot water” (DHW) fairly cool so we’re within the efficient range of the heat pump. For example mine is at 37 °C because my computer kicks in a Legionella run if the water hasn’t been hot for a few days anyway. You might find your NIBE SMO20 has a way to stop the “immersion” and Legionella activity. Specifically, my immersion is still reading “0” after 2.5 years because I’ve never used it. Even when my heat pump is inefficient, it’s still more than 100%. Even if you do decide to keep using it (which might be a good idea in your system) you would at least be able to correlate your change with the “whole house” power you are measuring.

Let us know if that helps or if it’s confusing and you’d like us to word it another way (or maybe just not worry you about it :slight_smile: )



Hi David,
Thanks for the reply! The red box is indeed fed by a black wire from the SMO20.

The thick cable from the fused spur is labelled ‘Immersion’ which supplies the NIBE HR 10 (to the right of the broom handle, lower box).

HR 10 is described as:

Auxiliary relay HR 10 is a connection box housing a contactor and a rotary selector switch. It is used to control external 1 to 3-phase loads such as oil burners, immersion heaters and pumps.

The other fused spur is label ‘Incognito’ which is the name of the company that installed the kit. The power cable from this spur appears to go to a box with a reset button that sits on top of the cylinder tank, out of shot of the picture.

Unfortunately, I don’t have access to a thermal imaging camera just now, but will see if the wire is warm to touch when the energy use is suggesting DHW heating is taking place.

Interesting comment about the temperatures, it looks like my system is running much warmer, so potentially some efficiencies to be made here…

Screenshot 2022-02-21 at 04.02.46

Screenshot 2022-02-21 at 04.01.34

The SMO20 is set to manage DHW demand in ‘smart control’ with very little in the way of helpful explanations. HomeAssistant is doing much of the automation around heating, dropping the thermostats a couple of degrees at night or if we’re out of the house, but nothing for DHW. I don’t know what the Nibe’s smart control for DHW is doing.
Screenshot 2022-02-21 at 04.06.01

I don’t have a schedule set up to switch the DHW mode between the above options, but that is possible with the SMO20, although there doesn’t seem to be any options to manage the actual temperature of the water, which as I write this at 0400 due to the god awful weather outside keeping me awake, the DHW temp sits at 49.2, for some reason.

Lastly, here is the chart from HomeAssistant showing household energy use and various stats from the ASHP. I’m looking to quantify energy use for DHW production, which would be indicative of the area highlighted by the red box, and likely attributable to ‘Hot Water Charging’ and ‘External Flow Temp’ increases.

Have I understood everything correctly? :crossed_fingers:

That’s some good sleuthing there Nick.

Around 14:00 the “hot water charging” temp keeps rising even though the flow temp doesn’t. Do you think it was heating via a solar diverter or the immersion or something else may be?

Your power consumption between 11:30 and 14:00 looks similar to when you were doing “S1 Room heating” later so it is tempting to suggest the heat pump was running for a while and the “hot water charging” go to about 47 then something else pushed it up to 53.

However, around 15:00 there is another push up in your “external flow temp.” to 53 with a corresponding power spike. It would seem odd for it to spend 30 minutes doing a de-frost when it’s 5 degrees outside.

BTW your flow temp between 18:00 and 23:00 looks pretty happy but then goes really high. And again during thee night. It’s a shame it’s not carrying on being gentle.

Would it also be fair to say the shower at 19:00 brought the “hot water charging” temp down and then the warmth in the room brought it back up to 20+ or is something else causing it to gently rise?

They’ve put some effort into describing what the modes do, except for “smart control” :slight_smile:

David, Thanks.

I’m keen to learn more and suspect the household heating is ‘ok-ish’ in terms of efficiency, but think there is definite room for improvement with heating the water.

We’ve no solar here yet, it’s on the way! At the start of the area marked by the red box the dive ‘hot water charging’ is me in the shower, and I’m associating the energy use after that with the ASHP re-plenishing the hot water supply. The brief spike >5kw is the kettle going on, which usually adds 3kw to whatever else is happening.

I’ve just had a Shelly EM delivered and plan on clamping CT’s on the hob ring and the ASHP ring, to give me definite ASHP usage. But at the minute I see a strong correlation between energy use and changes to the ‘external flow temp’ which allows me to judge ASHP energy usage. ‘S1 heating’ is heating occurring anywhere in the house, so, energy use without ‘S1 heating’ must be used to heat DHW? I’d still like to be able to quantify this, but might need someone with more smarts than me to do some clever stuff in HomeAssistant.

I think the temp increase you refer to must come from the immersion (hence the earlier train of thought around measuring the energy use at that fused spur you mentioned)

You said it is normal to keep DHW at 37, which sounds like a huge efficiency over the 53 that this system is heating to. I wonder how I might regulate that?

Yeah… no idea. I can check to see if the ASHP logged that it was defrosting, but I doubt it was. It could be the induction hob, although the spikes around 1730 - 1800 are definitely induction cooking. Given the rise in ‘external flow temp’ I minded to think it is the ASHP, but not sure why.

Agree… It’s like it pushes the ‘external flow temp’ super high before the heating turns off?

This is bath time for the baby! I wonder if the ASHP has prioritised heating (S1 shows sustained heating) over DHW for a couple of hours then started to replenish the hot water later in to the night? That would make sense, but is unhelpful since we’re unlikely to need DHW again until the morning.

What would you recommend? I’m tempted to move away from ‘smart control’ for DHW. We both work shifts so showering time can be anything from 0500 to 2200, and Hugo’s bath time is pretty much fixed at 1800 - 1830. I could schedule the DHW to switch between economy and normal modes (or even ‘Off’) but how much lead-in time does a system like this need, if for example it was powered off at night at switched to normal to ensure DHW for the morning?

Thanks for your help with this.

Edit to add:

Here’s the Hot Water Top, from the past week, I’d say the temps are definitely topping out to high?

Here is hot water charging, I wonder what happened on the 21st when the system decided not to replenish the DHW supply as quickly? Again, could have prioritised heating I suppose.

Hi Nick,

Ideally you could just set it in the main device, but I’m afraid I’m not familiar with the NIBE ones.

I’m afraid to say there’s a few of us sending commands over the web to MELCloud. Some of the others are using emonPi and friends to send commands over MBus to the heat pump directly. @TrystanLea is your person for that, but you might want to take a peek at the shop:

Honestly? I’d recommend playing with Hugo and not worrying about your heating system unless you really need to save the money. He’s only young once and no amount of fine-tuning the heating / hot water will be as rewarding as spending time with him. Put it in normal or even lux and try not to worry about it, especially if you are on brutal shift patterns.

If you feel comfortable lowering the peak temp, try that. If nothing else it’ll stop Hugo scalding himself. You’ll still probably want to bump it up high for Legionella once in a while, that seems to be a matter of personal opinion. I’m not suitably trained to advise you on that. Of course you’ll find the Legionella run surprises Hugo and he’ll use the really hot water that time! That’s what happened to our little one when we had mixer taps everywhere and we went to someone else’s house.

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Hey, thanks for the reply.

The Nibe kit has an API so sending commands to it is entirely possible but definitely no setting (that I have access to) for max temp. It’s due a service so i’ll ask the engineer to see about it.

You’re right, it’s not a priority (a lot of this tinkering gets done on night shifts during a lull at work) but our household electricity usage is high and we worry about the economic impact, and to some degree the financial aspect, given the cost of energy prices that are looming, so it would be nice to efficient.

If i do get the energy monitoring sorted I’ll post back.

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