Monday, 8 June 2015

How hard can it be?

I wonder if I can hack and re-write the controller for my air-con?

I am not asking for much, and for the air-con this is a simple job. I have a 5m x 5m x 2.4m cuboid room with door and window closed, one person, and one computer. It has one job - keep the room around 21.

It is a powerful unit, and this is the first springtime I have had it trying to do its job.

It seems, when heating the room, if I set it for 21 it will set the room between 21 and 22, roughly. That is fine.

However, when it gets warmer, it switches to cooling mode. In this mode, even saying to cool to 23 it will make the room between 19 and 20. I have to set it to around 24 to work sensibly.

The problem then is that it can decide that it is now too cold, switch to heating, and make the room 25 or more, which is getting silly.

If it is overshooting, which I can understand, then surely the code can understand that, and can act accordingly. Heck, it could even learn how the room behaves if it tried.

P.S. Set to cool to 24 it actually allows the room to go to 21.7 and a few seconds of cool air back down to 21.5 so a really good narrow target, just way off what I set!

15 comments:

  1. You can solve one of your problems by switching from "Mode: Auto" (shown on the left) to "Mode: Cool" or "Mode: Heat" as appropriate, which will prevent it from swtiching between cooling and heating.

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    1. Yes, but that would defeat the whole point of having a computer, which is no doubt many times more powerful that those on which I first played space invaders, running it for me!

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    2. In my view you're wasting your time and energy with a non-problem. I would never use an aircon in automatic mode, precisely for the switching hysteresis issues you describe. I don't need a computer to work out if it's too cold or too hot for my liking, and I switch the aircon to heating or cooling accordingly.

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    3. To be honest that is very defeatist. Yes, I could constantly consider if too hot or cold and set heat or cool - heck, why even have a thermostat in the first place. It is not rocket science to handle this in software, and would mean I am just comfortable with no need to adjust anything.

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  2. This is relatively normal for a combined unit - they do tend to heat to slightly above their cut-off point, then cool again and repeat bouncing back and forth.
    I've noticed the climate control on the landie doing something similar.

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    1. At this time of year, I expect a lot of the time it would not be heating or cooling as the temperature is mostly within the target.

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    2. I disagree actually, temperature will fluctuate due to clouds passing over which block the sun for a period, during which the temp will drop slightly :)

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  3. So are you going to reverse engineer it's communications protocol and then build a new controller for it?

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    1. That was one thought - only possible issue is the extent to which it beeps every time it gets a new command from the remote. That would, I am sure, be easy to disable with wire cutters...

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    2. If it's not an entirely consumer-y unit (I suspect you went slightly overkill, like I did for mine) then you can cut out the middleman, and go straight to the controller inputs, with a controller of your own devising. Should a serial line inside of some flavour (might just 2 wires, my daikin one was), and as it sounds like you have a wall-mount unit, it may be buried under the fascia, as multiple controllers is meant to be the realm of installation engineers, not end-users.

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    3. You can skip the IR bit if you prefer, and go straight to the wire protocol that the controller speaks to the head unit. Sounds like you have a wall unit, so you'll probably have to take the plastic off to find it, but likely there's a simple serial interface that the IR receiver/controller (and optionally other/external wired controllers) hook into. I suspect the insufficiently smart brain is in the IR receiver, and although I wouldn't be stunned if the temperature sensor was in the remote, I suspect it's also in the receiver. You get to replace all of that with your preferred combination of brains, connectivity and sensors to feed the brain.

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  4. Part of the problem is due to the airflow. When cooling it blows out cool air but sucks the air in at the top of the unit and this is normally where the temperature sensor is located. If the fan is set to a quiet low speed then you get the cool air sitting at the bottom of the room and the thermostat reading the warmer air near the ceiling.
    When heating you have the opposite effect when the fan is low in that the warm air coming out goes directly up making it think the air temperature is higher so it switches off. You will find wall units often don't have a very slow fan speed setting when in heating mode because of this.
    Your issue might be a combination of these factors and you might find it works better if you experiment with the fan speed and air direction.

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  5. Just put a fan heater in the room heating and the AC cooling then you will get a stable temperature. !!

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  6. Easy enough. I did this with an £8 thermostat PLC from eBay, on my fridge that was playing up. Check out:
    http://www.instructables.com/id/Home-automation-101-fixing-a-fridge-freezer-with-a
    Shouldn't take more than an hour once you've got the covers off.

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  7. All air con units have crap control software in my experience. The one at work is all over the place in terms of temperature.

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