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Air Source Heat Pumps (ASHPs)
Last Post by cathodeRay 6 months ago
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cathodeRay
 cathodeRay
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Topic starter 16/01/2024 12:35 pm  

Posted by: @scrchngwsl
↑

I've had success with this £6 sensor attached to a Raspberry Pi

Yes, I came across Raspberry Pi solutions, but it means adding a whole new layer of complexity which I think I could manage technically (can solder without burning holes in things), but I do like simplicity. The modbus setup I have is one cat5e cable connected via a RS485 to USB adaptor to a USB port which also supplies the voltage needed to run the XY-MD02 sensor, with the Midea wired controller (and any other sensors I may add) daisy chained to the modbus cable. Python's minimalmodbus module then collects the data. It is simple robust and reliable.

The XY-MD02 sensor (paid £11 on ebay) is about 3" x 2" x 1" and looks like this: 

image

 

As you can see, it is clearly not weatherproof, and even direct sunlight could I suspect cause false readings. I did think about some sort of cowl for it, but again it may lead to aberrant readings if there isn't enough free flow of air. Finally, after yet another search online, I have come across a couple of 5V modbus enabled temperature/humidity sensors that claim they are waterproof to IP67. They are either obviously from China, or likely from China, given the delivery times, but one way or another I'll get one and hook it up. I will then - hopefully - have the true OAT.

 

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


   
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cathodeRay
 cathodeRay
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Topic starter 16/01/2024 12:58 pm  

Posted by: @mikef
↑

How can this be a coincidence?

It is certainly interesting that the numbers should be so similar. Looking at the last week's use, to 0700 yesterday (Monday), it is still in the same ball park, 1.13. I am currently taking daily readings from the external meter, and will post results once I have a weeks data. It will be interesting to see how the current cold weather affects things.  

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


   
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cathodeRay
 cathodeRay
(@cathoderay)
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Topic starter 16/01/2024 1:01 pm  

Posted by: @derek-m
↑

I hope that the above makes sense.

Thanks for such a detailed description in words. It really does help my understanding of what you are doing. 

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


   
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