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...  

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.

(1) energy in: I have two sources for this data at the moment, the dedicated external Eastron non-modbus kWh meter that supplies the heat pump, and the Midea wired controller cumulative totals. Over short intervals (hours/days) the two can differ somewhat, but over longer periods (months) they are faily close, within about 2.5% of each other, with the Midea numbers almost always being smaller than the external meter numbers (meaning Midea based COPs are marginally better than those based on the external meter, but only by about 2.5% over the longer term). 

At the moment I read the external meter manually. It does have a pulse LED and pulse counters do exist but it seems they might be prone to flakiness and they are not simple, it means adding layers of cost and complexity. Eastron do make a modbus enabled version of the kWh meter I have (SDM120) but that means changing the meter and at present I am not convinced it is necessary, since I already know that the Midea wired controller cumulative kWh numbers are close to the actual numbers (see above). Given that, I plan to use the Midea kWh in numbers, maybe with a small correction applied, and consider that they have been verified against the external meter. Should an opportunity arise, I might fit a modbus enabled SDM120, but it is not a priority right now.

(2) energy out (raw data needed is flow rate, LWT/RWT delta t and specific heat of circulating fluid): the first question is where to measure it. Midea will be measuring it inside the heat pump itself, where the values will be at their highest, and best. Arguably, the most meaningful place to measure it is at the outlet (rad circuit) side of the heat exchanger, since that is the net energy delivered to the house, in the same way that horsepower at the road wheels is a more meaningful measure than horsepower at the flywheel in a car. But the rad circuit has no flow meter and no viable proxy, for example from the circulating pump, to use to estimate flow. This means that to measure energy out at the rad side of the heat exchanger would mean adding a third party energy meter at that point, not cheap, and not easy (space is very tight, and there isn't a convenient straight run of pipe in the vicinity where it could be fitted.

As it happens, there is a very basic analogue flow meter in the primary circuit, and it confirms that the surprisingly static Midea reported flow rate on the primary circuit is probably correct, meaning I have an albeit rather crude Mark 1 eyeball based external verification that the Midea reported flow rate is correct, or at least good enough. That means that all I need to measure energy out at the input side of the heat exchanger is a couple of temperature sensors, one on the flow pipe, and one on the return pipe. Taken together, the analog flow meter and these two temperature sensors will give me a Midea independent figure for energy out.

Now, I imagined that modbus enabled temperature sensors would be widely available, but it seems they are not, or if they are, I am not looking in the right places. After a lot of digging around, I have come up with the following proposal:

(a) temperature sensors: the well known and affordable DS18B20 sensor. This comes in various form factors, the stainless steel enclosed one perhaps being the best suited to pipework attachment using cable tied, and can be got from UK sellers on ebay for about £3 a pop.

(b) the DS18B20 output is analog (a resistance that varies with temperature?) and I need to convert that to a modbus value, and there seem to be remarkably few adaptors that can do this. The only thing I have found that appears capable of doing so - it has the right voltage in requirements (I have USB power available on my modbus cable, ie 5V) and the right modbus setting (9600 baud etc) - has to come from China. It is listed (on ebay) as a "DC5V 12V TTL232 RS485 MODBUS RTU Module PLC DS18B20 Temperature Sensor Module" and I plan to use the bare (no sensor version) 5V RS485 version, and will attach the DS18B20 sensors myself (although the listing doesn't show this, I am pretty sure they can be daisy chained, and each given a unique address). On the other side of the module are VIN (voltage in), GRD (ground) and modbus A and B connections. It looks like this:

I wonder if anyone has any thoughts or comments before I set about ordering the hardware? Have I missed another simpler (note that I personally do not consider HA simple...) way of doing this? Is my proposal flawed? If it is, I will surely find out in due course, but if someone knows that it is flawed in advance, then I can start to look for another way. And please, can I ask, don't forget the title of this thread: it is a beginner's guide. That doesn't mean an idiot's guide, instead it means someone who knows how to use a screwdriver and a soldering iron, but has never done so before (and so is a beginner) when it comes to heat pump monitoring. 

By dragging with the mouse, I can zoom into areas of interest. Here's data from the 5th April, a useful period to look at as it was cold overnight and warm during the day:

Plenty to be getting on with, to be sure!  

"Der Zugriff auf die Parameter oder Änderungen sind nur qualifiziertem Servicepersonal gestattet, das die
gesamte Verantwortung übernimmt. Wenden Sie sich im Zweifelsfall an Clivet."("Access to the parameters or changes are only permitted to qualified service personnel who have the assumes all responsibility. If in doubt, contact Clivet.")

The last word is the key, because Clivet is an Italian company. A search finds about the establishment of a new work by Clivet:
"In 2016, thanks to the industrial partnership with the Midea Group, Clivet has ..."