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Adding auto-adaption to a Midea heat pump controller

cathodeRay · 2023-10-29T15:08:06Z

I'm starting a new thread for this, because although it has come up in many other threads, there isn't a dedicated thread for the topic yet. By auto-adaption I mean a way of controlling the heat pump that uses more than just OAT (outside air temp) to set the heat pump output, with a view to getting tighter control of the IAT (indoor air temp) in varying conditions that may arise for whatever reason, be it from solar gain to an overnight setback. I will be doing it over modbus, and the principles if not the details should apply to any heat pump that can be monitored and controlled over modbus. It may well be that I am in effect trying to do a DIY attempt at Mitsubishi's auto-adaption, or Homely's control systems, but I have nothing to do with either of those capers, even if my objectives are broadly similar. I am going to start with the idea that all the many factors that affect the IAT can be summarised in one proxy variable, the difference between the actual IAT (aIAT) and the desired IAT (dIAT). If the aIAT is above the dIAT, then the sum of all the factors heating and cooling the house add up to more heat is being added, or less heat is being lost, than is needed, and vice versa when the aIAT is below the dIAT. This approach greatly simplifies things. I don't need to know what the factors are, let alone measure them, instead, I just monitor the end result, the aIAT, and compare it to the dIAT. I can then adjust the one thing in all the factors that I can adjust, the ends of the weather compensation curve, which can be done over modbus, with a view to moving the aIAT towards the dIAT. At the moment, there is not a lot going on weatherwise, still relatively mild, with an OAT of arounf 10-12 degrees C, and my aIAT is just a bit above the dIAT of 19 degrees. Here is the chart for the last week, with some other variable also plotted: BTB - emoncms, please note how everything needed to make sense of the chart is on or by the chart. This chart suggests that, for the prevailing conditions, my WCC (weather compensation curve) is just a little too high. However, I can't tweak the middle of the WCC (which is where we are with the prevailing conditions), only the ends. The 'curve' is in fact, according to the Midea literature, a stepped linear line from the left hand to the right hand end, meaning I will have to adjust the ends. I am going to run this timed python script (the logic should be easily grasped) and see what happens, but before I press the red button (run it in the real world), does anyone have any comments? import minimalmodbus import serial from datetime import datetime import schedule import time import os import sys # I think these are needed to keep things running smoothly... os.fork() and sys.exit() # set up the wired controller connection instrument = minimalmodbus.Instrument('/dev/ttyUSB0', 1) instrument.serial.port instrument.serial.baudrate = 9600 instrument.serial.bytesize = 8 instrument.serial.parity = serial.PARITY_NONE instrument.serial.stopbits = 1 instrument.mode = minimalmodbus.MODE_RTU # set up the aIAT sensor connection (uses the same serial settings as above) instrument_MD02 = minimalmodbus.Instrument('/dev/ttyUSB0', 3) instrument_MD02.mode = minimalmodbus.MODE_RTU # set the desired IAT dIAT = 19 def 15minCheck(): # get a datetime for logging now = datetime.now() now = now.strftime("%Y-%m-%dT%H:%M:%S") # get the aIAT (it is reported as x 10, ie 12.6 as 126 so need to divide by 10) IAT = instrument_MD02.read_register(1, 0, 4)/10 # compare the aIAT to the dIAT and set (or don't set) the ends of the WCC accordingly if aIAT - dIAT > 1: # house is too warm, lower ends of WCC by 1 degree C instrument.write_register(265, instrument.read_register(265, 0) - 1, 0) instrument.write_register(266. instrument.read_register(266, 0) - 1, 0) with open('./modbus/auto_adjust_log.csv', 'a') as f: f.write(f'n{now},{aIAT - dIAT},-1') elif aIAT - dIAT < 1: # house is too cool, increase ends of WCC by 1 degree C instrument.write_register(256, instrument.read_register(265, 0) + 1, 0) instrument.write_register(266, instrument.read_register(266, 0) + 1, 0) with open('./modbus/auto_adjust_log.csv', 'a') as f: f.write(f'n{now},{aIAT - dIAT},+1') else: # house is close to where it should be, do nothing except logging this with open('./modbus/auto_adjust_log.csv', 'a') as f: f.write(f'n{now},{aIAT - dIAT},0') # do the check every 15 mins schedule.every(15).minutes.do(15minCheck) while True: schedule.run_pending() time.sleep(1)

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Air Source Heat Pumps (ASHPs)

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cathodeRay

(@cathoderay)

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Joined: 4 years ago

Posts: 2935

Topic starter 30/10/2023 2:41 pm

Posted by: @derek-m

↑

I am pleased to see that you are resisting the urge to 'tinker'. I think that you will find it could takes several hours for the IAT to reduce and stabilise.

It's called masterly inactivity...

Posted by: @derek-m

↑

One improvement that you may wish to consider is varying the offset dependent upon the size of the deviation.

Something along the lines of:-

If the deviation is <0.5C, do nothing.

If the deviation is =>0.5C, offset by 1C.

If the deviation is =>1.5C, offset by 2C.

I had had similar thoughts, thinking about recovering from an overnight setback, for example, when the deviation is likely to be greater.

I have just had a peek at the live minute data for the last 12 hours (auto_adapt went live at 0800 this morning) and the LWT and energy in have gone down a bit, whether due to the increased OAT and/or the auto-adaption, and the IAT has dropped by 0.1 degree C...

This is on a par with watching the paint dry. But that's OK for now, I just need to get a feel for what the increments need to be by trial and error.

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

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