Installing monitoring on an old system

we have a ground source heat pump system installed in 2007 and an air source system installed in 2014. I am thinking about installing a monitoring system to enable me to check the efficiency of the installations and hopefully find away to reduce costs.

We do not have a smart meter and currently get our supply from Octopus. We also have a small PV installaton (4kw). Our consumption at present is around 18000kwh per annum on an Economy7 tariff.

I would be interested in any information regarding the feasibility of installing a monitoring system.

Hi @mikejd, welcome to the community!

It’s super-feasible and you can choose how detailed you want to get.

In your case I think you probably want to monitor the main electric feeds to both heat pumps and their flow/return temperatures.

You possibly want some monitoring on your import/export and solar.

The actual monitoring gear you use will depend on where you can safely get access to the +/- sections of the cabling, usually in/around a consumer unit. For each supply you want to monitor you need to clip a CT (current transformer) around either the positive or negative cable, but not both.

You will need a plug socket nearby to power the monitoring device(s) and to allow the device to work out what the voltage is and in which direction is monitoring.

For the flow/return temperatures, the basic option is attach some DS18B20 temperature sensors to the relevant pipes, there is help on how best to do this in the documents section.

Have a look at the shop at: emonTx, emonPi and emonBase. These have varying numbers of inputs for the sensors you will use.

Make a list of all things you would ideally monitor and work out where the best location(s) are to have the minimum number of devices.

In the fullness of time you may want to go into further detail, adding heat meter(s) if you think you may have a problem, but the best thing is to just get started. (If you have any old raspberry pi’s laying around you can use them for gathering temperature data and with the addition of an inexpensive board from the shop can turn one into an emonBase.)


I don’t know what you mean by this. Certainly, you can’t use a c.t. on direct current (from your PV panels) - it will not work.

Do you actually mean Line and Neutral (the cable cores are coloured brown and blue respectively) and by “both” you mean not a flat grey twin-core plus earth cable? I think you do.

I do.
I knew I’d get pulled up on something in that post :joy:

I guess I would need separate systems for the ground and air source as they are in different parts of the building. Can you monitor room heating and water heating flows separately? Would the PV generation be separate also?

I have 4 devices which I have changed the layout/use of over time:
2 emonTx - solar, import/export, battery
1 emonPi - heat pump
1 emonBase - collect the above together (was doing with the emonPi but did this to lighten the load)

What you can measure on one “sensor node” (e.g. emonTx, emonTH) depends very much on what the sensor node is capable of, but more importantly on the physical constraints, such as where you are able to locate sensors, obtain power or run cables. The new emonTx4 with the extender board can monitor the power in 12 circuits, but it cannot (yet, maybe never) measure temperatures. There’s no point in having the extender board if it’s too hard or too expensive to bring the cables for the last 6 to the same place as the first 6.

For @mikejd’s benefit, an emonBase is a Raspberry Pi with just an ISM band radio receiver added. It runs emonCMS, it can handle inputs via radio, LAN or serial USB, or temperatures and pulses with a direct connection. It can’t measure power.
An emonPi is a 2-channel emonTx and a Raspberry Pi in the same box, so it can do as the emonBase but with 2 power channels on top.

I’ll have to try to get my head round this, and try to work out where things can be installed. I’m sure I will have lots more questions.
Incidentally, I have an early model Raspberry Pi, I think model A or B, which has never been used. Would this be suitable for this application?
Thanks for all the info so far.

I’m using a B with the additional board (an older version of rfm69spi) for my emonBase.

A while back I set up my oldest RPi (2013?) to handle 11 DS18B20 temperature sensors although I’m not running that at the moment.

A B should be OK, an A might be a challenge.

I’m running the Nov 22 version of emonCMS on a 2B. It’s a bit slow presenting a graph of 8000 points, otherwise it’s fine.

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@christian I have been looking at the connections I would need to make and I have attached a couple of documents showing the installations.

For the ground source pump, I think I would need CT connections to the heat pump circuit and the PV circuit, plus temperature sensors to the flow and return. I then need a emonTx and an emonBase. There would be a power socket close by.

For the air source pump I can see where to put temperature sensors on the flow and return but the cables appear to be run behind the plaster board. It may be possible to install a CT sensor inside the pump housing but I am not sure. I would need an emonTx here with radio connection to the emonBase. I would need to sort out the power supply.

Does this look workable?

That sounds reasonable but if you’re planning on getting that kit I’d check with the guys in the shop.

Have you seen this guide to placing your ct-sensors? (please be safe!)