Simple Air Conditioning Controller Project

[jucole]

A little while ago a beginner member posted a message requiring some help on the software side of creating a controller for his air conditioning unit and I've offered to help out.   So I thought it would be a good idea to start a fresh post.

I know very little about air-con or Arduino but I've been doing a little bit of reading, and I think it looks fairly easy.

The aim is to create an open-source air-con controller using an Arduino Uno to control his specific air-con unit but hopefully the finished project could be easily modified / extracted onto a simple PCB without the need for the Arudino dev board to perhaps control other air-con units.

The reason why I posted here is because I thought it might be interesting to others who might be doing something similar; also if anyone has done this type of project before could offer helpful advice - because we will probably need it ;-)



In the text below I will update with the latest specs / schematics and files as the project grows.


Specs:
Designed to fit Air-Con model: ??

Features:
Ethernet

Inputs:
1). Room Thermistor
2). Coil Pipe Thermistor?

Outputs:
1). Compressor
2). Fan Motors High
3). Fan Motors Low
4). Swing Motor

Schematics:
Arduino Uno + ??

Files:
??

[rastro]

I have a GE window A/C that has a IR remote.  My guess is that many A/C's in the last 5-10 years probably have this feature.  This would be the easiest way to instrument control through an arduino since there are existing library's for IR remotes.  The same is true for humidity and temperature sensors.  Modules for IR, temp, humidity are really available.  This reduces the need for customized circuits - i.e. off the shelf solution.   

The remaining problem is for the arduino (controller) to know the current operating mode of the A/C unit. 

[jucole]

I have a GE window A/C that has a IR remote.  My guess is that many A/C's in the last 5-10 years probably have this feature.  This would be the easiest way to instrument control through an arduino since there are existing library's for IR remotes.  The same is true for humidity and temperature sensors.  Modules for IR, temp, humidity are really available.  This reduces the need for customized circuits - i.e. off the shelf solution.   

The remaining problem is for the arduino (controller) to know the current operating mode of the A/C unit.

Yeah, good point!   once I know more about the A/C model we can look at the options, but I think it will be more of a bare-bones controller, but built as a learning experience.

[Andy932]

Hello im the guy working on the project the problem with the ir control is there is no feed back from what the unit is doing. So i m working on a control unit to replace the main control unit so i can have full control and also get feed back from the unit itself. In the end the ac unit will look like it allways has but with a network interface for remote control. I had built a control be for for it but i couldn't program it so i left it. Im now working on a newer more advanced but simpler controller for it. I will post a schematic once i get all the parts together for the new controller. If anyone has done ir be for pls let me know as I'm also looking into using the old ir remote as a later add on for local remote control.  Im going to start it of as just a basic replacement controller and then add on from there.

[Mechatrommer]

swing motor doesnt need to be automated, its just turned on or off based on user selection. it leaves to 2 motors to control, compressor and indoor fan. setting cut off temp (room thermistor) and hysterisis should be easy in software. but you dont pick temp (coil pipe thermistor?) as you please since some thermodynamic jargons such as dewpoint or coolant feezing or liquidifying (or what) during compression stage re-entry need to be avoided. liase with your mech.eng friend about this, he probably will give you graph or formulation for the automation, its been a while since i played with those graphs.

[Andy932]

Ok yer totally forgot about that with the cooling pipe. I will look into it sum more.

[rastro]

Hello im the guy working on the project the problem with the ir control is there is no feed back from what the unit is doing.

One possible feedback source is indicator lights on the unit's front panel.  These could be selectively read by photo sensors.  In the case of 3 fan speeds you would only need to monitor one light since these typically cycle through.  So you could treat that particular indicator speed as the "home" position and assume the other speeds are in sequence.

Draw backs:
1. The unit may not have light indicators - then back to hard wiring.
2. Clutter/kluge to the front panel - but if there's a remote you may not need to access the front panel.   

[IanB]

Hello im the guy working on the project the problem with the ir control is there is no feed back from what the unit is doing.

What you are trying to do there by replacing the wall thermostat is known in industry jargon as "direct digital control". It is possible, but not always the most effective way to go. You rarely want to replace the local control loop in a control system.

What is more often done is "supervisory control" where you leave the local control loop in place and send it commands to tell it what to do.  The equivalent here would be to interface to the wall thermostat. You would send it on/off commands and temperature settings and read back the measured room temperature.

IR could do what you need except for the read-back feature. But if you have a reliable link you don't necessarily need any read-back. You could trust that your commands are getting through.

[Andy932]

Ok this is wat i want the unit to be able to do. I want it to be able to send temps fan settings and other basic info to a web interface. From that interface i want to have vitrul display panel like the one on the unit so i can remotely change the temps and also turn it on and off and also set fan speeds. I also still want to be able to manually controll it if the network goes down. Basicly i will take the old controler out and put in a new local interface with a network interface with on board web host for the web interface. Thought id just clear that up. It will be built into a stock case so it looks like its the original controler but with a network port as extra. Atm i m just working on replacing the controler with my own i will then try to add on the network interface and other things if i can. But as iv never done any programing apart from the basic control a relay and blink a led any help would be great. Im looking into the network interface atm and if anyone could help me out with that then that would be great as i have no clue as how the Ethernet shield for the UNO works.

[paul23]

It´s going to depend on the type, age, style and manufacturer of the air conditioning system as to how you do this.  Inverter systems are going to be a massive task to do because they have quite complicated controls, it´s not as simple as switching a compressor on or off, there are many variables to control. 

If it is a simple on/off style system then that is easier.  Generally you will have 5 cables (or 3 for cooling only) between the units.  These would Compressor live, neutral, heating valve, fan, earth.  But not necessarily in that order.  Some models also have another thinner pair which is an ambient temperature sensor.  On these types of systems there is rarely any controls in the outdoor unit.

The controls are quite simple, a relay to switch the compressor, a relay to switch the heating valve, a relay to switch the outdoor fan.  The internal fan is usually 2 connectors, 1 to drive the fan speed and one to check the speed of the fan.  This is to stop the motor if the fan has seized or is spinning too slowly.  The louver motors are just small stepper motors, easy to control, but you must make sure you don´t try to turn the motors too far or you will destroy the motor,  the louvers can't physically turn 180º  without getting jammed and the motor won't stall, it will destroy itself.  That´s it for power stuff. 

There are normally only 2 sensors, 1 detects the coil temperature and the other room temperature.  The coil temperature is the most critical one.  It has 2 functions, in cooling mode it is there to prevent the indoor unit from freezing up, in heating it controls the fan speed to maintain the evaporator (which is the condenser in heating) at the right temperature or to stop the fan when the evaporator isn't hot enough (so you don't get cold air blowing out when the unit first starts).  It is also a safety device to stop the compressor if the evaporator gets too hot in heating. 

Other than the IR receiver and any flashes LED´s that´s it to the simpler models.  If it´s an inverter type, then forget about it, it would take all this page for me to describe how they work and even then you would have 100 questions, and it differs between manufacturers.

It would be very difficult if not impossible to do a universal controller because of the differences between manufactures, seriously they are not even similar.  A lot of the chinese one´s I guess you probably could get something that might work and if you are just sending IR codes then that would be possible, but hard.  Simple on/off style are pretty much extinct here now, everything is inverter and a lot more complicated.