A Beginner's Guide to Heat Pump Monitoring Reloaded (v2)

cathodeRay · 2023-04-01T19:06:55Z

The guide is dead, long live the guide. After months of torture by Home Assistant python sadists, I had to accept that playing Home Alone with Home Assistant was not for me. It's a pity, because Home Assistant (HA) appears to have so much potential, but as the core of a heat pump monitoring system aimed at beginners, it is just not ready for prime time. For coding experts and tinkerers with all the time in the world, I am sure it is just the thing, but for beginners — by which I mean interested lay folk with basic DIY and computing skills — it has three major, and in my view fatal, flaws. The first is that it tries to be all thing to all people, and the result is extreme complexity, which is not the beginner's best friend. The second is that the official documentation is often, but not always, almost impossible to make any sense of, and the unofficial documentation, the forum, is in large part a charnel house of dead threads, where the shattered bones of the long departed lie scattered on the floor in silent testimony to the unanswered question. I know in advance that the high priests of Home Assistant will say that I should WTFM myself, but frankly, my dear, I don't have the time. The third, and perhaps most serious flaw of all, is that it is unstable, and can trash your precious data at any time. With a lot of grubby hands on work, you might get your data back, but you will not be able to add it back into HA's database. Yes, you can, indeed should, have backups, but you will still lose any data collected after your last backup, up until the time of the crash. When I first set out on this long and winding road, I set myself a deadline of having a working system by today, the 1st April, as a sanity preservation device. I am relieved to be able to say I have met the deadline, and emerged, just about, with my sanity, though not necessarily all of my hair, intact. The steps I am going to detail in this thread will enable a beginner to set up a working heat pump monitoring system at the very least for Midea and Midea clone heat pumps, and very possibly other brands, including but not limited to Samsung heat pumps. If your heat pump uses — jargon will be explained shortly —modbus over a RS-485 interface, then there is a very good chance this guide can act as a generic guide that you can adapt to enable you to monitor your heat pump the way you want to monitor it. The key elements of the new approach are firstly that it uses a wired as opposed to a wifi connection, and secondly it uses, and only uses, very basic python code — I should know, I wrote it — to collect data over that wire, and then log it to csv (comma separated variable, the data items are in rows, each column separated by commas) text files that can be viewed, manipulated and charted using any spreadsheet. If you can work on a spreadsheet with basic formulae, you will understand the python code. Unlike a complex database, which is easily corrupted, csv files are extremely simple, making them both robust and easy to work with. The jargon: modbus is the language, or Morse code if you like, that allows two way communication with the heat pump, and RS-485 is the telegraph system that transmits the Morse code. As the user, you don't need to know the intimate details of RS-485, you only have to get and connect the physical wire and adaptor that makes the connection possible. For modbus, all you need is a table that translates the item of data you want into the Morse code, or register address, for that data. Modbus data is in effect a stack of data, a spreadsheet one column wide, where each bit of data can be identified by its position in the stack, or row in the spreadsheet. If you know its position, or row number, you can get, and in some cases set, the data. This last step, of setting the data via modbus, offers the possibility of not just monitoring your heat pump over modbus, but also controlling it. This has a number of potentially very useful capabilities, notably but not only adjusting the heat pump output depending on the load (call for heat) demand at any one time. The number of physical items you need is small, a mini PC, a USB/RS-485 converter that plugs into your mini PC, a cable to connect this converter to your heat pump controller and a small resistor — and that's it. This bundle of fun can be got easily on ebay for around £50 or perhaps even less; I will give details later. The only tools you will need are some small screwdrivers, plus whatever you need to route the thin cable through your house from your mini PC to your heat pump controller. The necessary minimum list of software you need, over and above your mini PC operating system, is even shorter: two python scripts that I will make available, and some sort of spreadsheet. Although the two scripts are written for Midea heat pumps, they should, as noted above, be adaptable to other brands of heat pump.Rather perversely, given my rants about HA, I have decided that at least for now, I a...

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Air Source Heat Pumps (ASHPs)

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robl

(@robl)

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Joined: 4 years ago

Posts: 205

03/10/2023 11:33 pm

I did made a heat meter - I used the tsic716 sensor (tho the one you point at is a lot cheaper, and similar accuracy, which is great). I connected two of them directly to an ‘mbed’ running Arm C code, bitbashing the sensors. The mbed is overkill - it doesn’t take a lot of processing power, although a low power lcd display would be nice. The same part measured flow (a square wave o/p sensor, frequency proportional to flow), and also electrical power - from a mid certified meter with an isolated optical pulse output. The mbed then calculates COP, displays it (add on 3 digit led display) and logs it (the mbed is a low power uP board, has an rtc, flash memory, both very handy for logging). Proper software engineers would hate the code- no interrupts, just does one measurement after another - takes a second or two to do the lot, fine as the heatpump and pumps run at constant speed.

What will HA run on? If it’s on a raspberry pi or similar, Googling ds18b20 and raspberry pi indicates there’s been a few projects connecting them directly - with a pull up resistor on the data line. Am I looking at the right part - it’s a one wire digital o/p part?

The sensors really need to be well connected - I ended up soldering short lengths of thin copper pipe to my flow and return pipes, that had the sensors pushed in, and insulating the whole lot. Just strapping the sensor on will almost certainly limit your accuracy. If you don’t want to solder, can I suggest fixing the sensor to the pipe with several layers of copper tape, then covering with at least 1cm of insulation, making sure there are no air gaps cooling them down.

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cathodeRay

(@cathoderay)

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Joined: 4 years ago

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Topic starter 04/10/2023 7:20 am

Posted by: @georgeedjones

↑

I’ve been hoping you’d do an update

I've been waiting for the heating season to start, once the heating is on I want to check and double check my monitoring system works as it should do, and then I will post the details. There are also some anomalies that need to be sorted out eg collecting the data and calculating the COP using different methods gives similar but not the same results, and I don't know which, if either, is right.

@robl - sounds interesting, but I have to say that one of my guiding principles has been simplicity - I want to have a system that anyone with enough interest and the ability to use a screwdriver without stabbing themselves can use. That effectively rules out Home Assistant (too complicated to set up, even in its 'green' incarnation) and raspberry Pis, arduinos and all similar hardware (again just too complicated for a novice who doesn't want to spend days leaning about such things). I don't want something that relies on proprietary or quasi-proprietary software (another reason for ruling out Home Assistant) because all too often the developers will introduce breaking changes and/or insist on arbitrary system requirements, and likely as not they will store the data in hard to access databases (I use csv files, very robust and accessible). The whole package also needs to be affordable - off the top of my head, I think I spent £50 or thereabouts in total.

In brief, I have a small fanless PC running linux (for historical reasons, it could also run Windows) with a wired modbus RTU connection to the Midea wired controller, USB connection at PC end, screwed wire connectors at Midea wired controller end. A simple, and I mean simple, python script uses the python minimalmodbus module to get data over modbus once a minute from the wired controller, and logs it to a csv file. Another simple python script then converts that minute data into hourly and daily data, and logs the hourly and daily data into their own respective csv files. For charting, I use a mixture of spreadsheets (another reason for using csv files, spreadsheets can chart then out of the box), highcharts.js and plotly in python. And that's it.

The obvious downside to this approach is that it is totally dependent on Midea data. If Midea cook the books (not an absurd notion at all, remember dieselgate), then my monitoring results will also be cooked. That said, I have taken some precautions to confirm that Midea aren't roasting the data before making it available, but I can't rule out a bit of gentle simmering.

Full details to follow...

Midea 14kW (for now...) ASHP heating both building and DHW

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