Say 240v and 10A for the full 60 minutes, then on for 30 minutes and off for 30 minutes during the one hour period. Then try different combinations of on and off timing.
Difficult to make that happen, I don't have direct control over the current. I do however have the external heat pump dedicated kWh meter which reads to one decimal place (and more if (when) I get an LED pulse counter). I could for now log that at hourly intervals and then see how the various methods compare to what it shows. A new fun way to spend one's time on a soggy Easter Bank Holiday Monday.
Indeed it is. The heat pump does generally under-report, but not by a huge amount, and the two lines do move in concert. I do agree with your two thoughts on why it under-reports, use of integers with unknown rounding, and only measures compressor current. Being me, I might also add that there may be a wilful blind eye to ancillaries current use, caused by the marking one's own home work effect.
Are you doing any area under the curve type calculations? Or just in effect summing the instantaneous readings on the assumption they are reasonably representative of the seconds either side of them?
Midea 14kW (for now...) ASHP heating both building and DHW
What's the HP actually doing in the area I've hatched?
Nothing different to what it was doing prior to that, I think it's just bad rounding creating artificial "steps" in the data (look at the blue line, it climbs slowly & steadily)
As you can see, the heatpump lags behind the Shelly (not surprising given the imprecision of the current) and consistently under-reports. I am yet to see it over report for more than a few minutes. This can be accounted for in part by the imprecision of the current as an integer (and who knows which direction it's rounding, my hunch is it's simply dropping the decimal), the rest can be accounted for in the ancillaries. The external pump on the other side of close-coupled tee uses between 40-100W depending on the state of the TRVs upstairs.
As such, I'll stick to reading the power in from the Shelly for now!
One of the things on my list is to report the power in/out to different sensors depending on whether the ASHP is in DHW or space heating mode. I'm less interested in the CoP of the heat pump for water, and more interested in the space heating performance, obviously DHW skews the results given the considerably higher flow temperatures.
Welcome from an another relative newcomer and newbie. I have a Midea 12kW with 22 radiators and a plate heat exchanger. I can relate to your input energy curves from EM, and it’s good to see how it relates to the modbus data.
I think the explanation of the Midea unit making an adjustment to improve the inaccuracy caused by the integer current reporting is believable. In general I don’t have much difference between the Midea daily energy and my measurements.
My rather powerful Wilo secondary pump uses 150w on its slowest speed. I deduct this when calculating COP. Today I wondered whether a Grundfoss Alpha 3 would be better as it can adjust automatically to load and has variable flow speeds. Given the Wilo runs at a minimum of 2.5m3/hour and the Midea can only run at 1.5 there seems to be a mismatch that I should address with the installer.
I have been looking at Open Energy Monitor recently because emonCMS etc has similar feature and there is additional hardware support for DS18B20 which I’d like to fit across the heat exchanger ports.
From reading your posts it seems the Freedom monitoring does do much that you can’t do with HA.
Some of my worries are disappearing as at present the COPs I calculate by hand using the Midea controller and Emporia energy monitor are consistent with the published data in the Midea Engineering documentation. Mostly 4.5 upwards.
I’d be interested in getting details of the integrations you have used, or do I just hunt for the Node Red stuff.
My meaning was to apply the 240v and 10A in the different calculation methods to see if there are any differing results. The problem with using live data that is varying, is which results should be correct.
By putting fixed data, the result for which you already know, it is possible to see if any of the calculation methods differ, and possibly understand why. Using 60, 1 minute values of 240v and 10A should hopefully produce the answer 2.4kWh from all calculation methods. Conversely, 30 values of 240v and 10A and 30 values of 240v and 0A, should produce the answer 1.2kWh.
60 x 10A, 240V: all simple spreadsheet calcs give correct answer, 2.4 kWH, python integration methods (np.trapz, scipy.integrate simpson) both fail, both produce 2.32 kWh. KISS 1, python sadists nil.
30 x 10A, 240V + 30 x 0A, 240V: all simple spreadsheet calcs give correct answer, 1.2 kWH, python integration methods (np.trapz, scipy.integrate simpson) both fail both produce 1.18 kWh. KISS 2, python sadists nil.
I may have got the python code wrong, I don't think I have, but who knows with opaque methods?
Midea 14kW (for now...) ASHP heating both building and DHW
What's the HP actually doing in the area I've hatched?
Looking at the scaling of the graph, it is obvious that the purple line produced from Midea data is using integers. The displayed value goes up and down in multiples of 240W, which equates to a change of 1A at 240v. There may be a slight delay because the readings are being taken at 10 second intervals, and it is possible that there may be some internal integration being performed within the Midea controller.
For obvious reasons it would appear that Midea are rounding down the measurements taken, which helps make the performance figures look better.
@transparent We have relatively short microbore off 22mm pipework. An extra radiator was added with 15mm pipework off the 22mm, but it doesn’t get any hotter. The Wilo is a TOP Z25/6! It was a bit noisy at maximum speed, but I was in ‘don’t fiddle’ mode.
I think the installer didn’t want to take chances. He did say after running the system that maybe the pump could be smaller, but who I am to know whether it would work at -9C!
Everything I told him supported the view the original pipework was well designed. I even ran the Combi at quite low temperatures for a while. The pump in the Vaillant was powerful enough to heat all the radiators without cold spots at bottom.
I’d be interested to hear if anyone has experience of Intelligent Circulation pumps. I feel I need to understand the relationship between the input flow/return and output flow/return temperatures to better understand that side of the system. The indicators are the primary loop reached a stead delta T more quickly than the secondary at a low target flow temperature. The heat pump works near maximum capacity in the warm stage before easing back. My gut feel is the heat exchanger cannot deal with low flow temperatures. I think I need a bigger delta T on the secondary circuit though but I need the temperature sensors across the input and output ports to be more certain.
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