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Old 02-07-18, 01:20 PM   #11
ThMihov
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Good evening everyone
Ron342,i like the idea for detecting the blocked air flow,but for now,I'll keep it simple and use a temperature sensor,because the forecast about the next week is talking about temperature drops and rain/snow fall,and i want to make it work until then and log some data,but for future improvement it's really a good idea
Great exchanger,i like it very much.I was thinking to use two 6mm pipes in parallel in 20mm PE pipe.In that way I'll have big heating area with small amount of water,which means greater output water temp and faster heating,but before i begin to experiment with the heat exchanger,i want to make some measurements on this setup.If you have some free time,i'd like to hear more about your exchanger,setup and results
As for the hardware/software-I'll try to explain the things in simple and at the same time detailed way.The setup is a nightmare-Arduino board with a bunch of wires around it,without any labels,but...
In an hour I'll try to explain the idea for the control

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Old 02-08-18, 03:43 PM   #12
ThMihov
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Little late,but...better than never
So finally explanation of my idea for controlling the AC.
Since it is a DC inverter,simply applying voltage to the compressor,doesn't work,because there's a PCB which converts single phase 230V 50Hz mains to 3phase voltage 120V (according to my memory,it could also be e different voltage,but it's there about) with variable frequency,usually 20-130Hz.Making VFD from scratch,and in home for such an application (kW of power,high voltage and current) combined with all the necessary protections is hard and time consuming,so there should be an easier way.Than i realized that all the above is made in the factory and is sitting in front of me,in the AC's case.So how to use it?.Simple-fake the control PCB of the AC,so it "thinks" something that in reality is not true.More precise-the room temperature,and the discharge pipe temperature.Since i need only an on/off mode of operation (or full-throttle),not a real speed regulation,it's sufficient only to simulate the pressing of the power button of the remote control to switch it on or off.I made that by capturing the codes sent by the RC (power on,power off,temp.up,temp.down and mode (cooling/heating) with the IRLib for Arduino(https://github.com/cyborg5/IRLib) and send them in the appropriate time to the AC by an IR LED,which i temporarily installed in front of the IR receiver of the AC,but in the final version i'll remove the receiver and solder the wires directly to the AC's PCB.
The next thing is to make the control unit "thinks" that the temperature of the discharge pipe and the room temp are correct for heating mode.The way i solved that problem is by replacing the original room & discharge thermistors with fixed resistor.The original discharge pipe thermistor was NTC 10k,which i replaced with 4.7k,and the room temp thermistor was 25k (or there about),which i replaced wtih 33k resistor.I have checked thermistor's values with a cup of hot and cold water,and chose the values of the resistors,so that if the room temp is 15C and the discharge temp is about 55C.Now when the AC thinks that it's cold in the room,it runs at maximum power,and when the discharge temp it's not changing,it doesn't go in to defrost mode,since it's not detecting temperature/pressure drop due to the icing of the exchanger.So the next problem to be solved is how to really defrost when it's needed?Unlike the compressor,the four-way valve and the fan are simple devices-it only need mains to operate .So the most obvious way to control them is to apply or cut-off the voltage on them.I have made this by putting a relay in series with the valve and with the fan,so i can turn them off independently of the AC's control board.In that way ,for example when the AC operates in heating mode,the valve is powered.When i need a defrost,i simply cut-off the power of the valve and the outdoor fan,using the relays,wait until the exchanger temp reaches 6C,than turn on the fan to blow out the moisture from the exchanger and 10sec after that i turn the valve on again.That way the AC thinks,that it's heating the room,but it's really in defrost mode,and when the defrost is done it really starts to heat the tank .Luckily the control board of the AC is simple,so it doesn't watch for outdoor fan's speed and no additional circuitry is required to emulate the working of the fan.The last problem i've solved was how to determine when the compressor is running or not,since again because of the fact that it's an inverter,the outdoor unit is supplied all the time,and simple opto-coupler circuit for detecting voltage is not going to work here.So i've placed a current transformer to measure the AC's current and in that way determine if it's ON or OFF.
That's all for now,because it's bed time.Maybe tomorrow I'll put some code with explanations and some pictures.Good night
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Old 02-10-18, 04:56 AM   #13
Acuario
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Hi, sounds like you are making good progress. I'm interested to hear how you progress with the controller. I previously hacked an inverter but in a different way to you. One thing I'm interested in is if you have any problems when you remove the power feeds to the air guide and fan motor. Sometimes there is feedback to the controller to detect failures so the machine will shut down if the fan isn't running. Maybe the machine you have doesn't have that so you won't have this problem.

IR blaster controllers are easy to find for Arduino. If you used an ESP8266 you could make it WiFi controlled.

Good luck with the project. Maybe some of my posts will help you as I've tackled the conversion of an indoor unit to a fan coil using water and several coil heat exchangers.

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Old 11-04-18, 09:32 AM   #14
ThMihov
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Hello again,after an year in which i was busy with other things and i stopped working on my project.
Acuario,no i don't have any problems when i disconnect either of them.Maybe the built-in controller isn't too smart .I admitted that maybe there will be a problem when disconnecting the fan,and i was going to measure the pulses of the fan's sensor with my scope,and build a simple circuit with 555 timer to emulate them.After all,it's just a simple Hall sensor-it gives square pulses at it's output .Fortunately i did not ran into this problem.
As for the controller-a hate Arduino's language (but i love the fact that there is ready library for almost everything which is ideal for fast tests) and a bunch of wires,so i bought an Atgmega128A which have plenty of memories so i think i could fit all the code inside,and i'll write the code in C++ as usual,because i like to know what happens in every moment,which is not quite that in Arduino's language.Beside of thath i decided to change the temperature sensors to LM335 beacause they are accurate enough and simpler to use.
The major change i have made before few days was that i replaced the water tank with the coil in it, with PEX-AL-PEX tube 20mm in diameter in which i put in a 3/8" (9.52mm) copper tube.The lenght is 10m.It's poorman's tube in tube heat exchanger,because brazed plate heat exchangers for R410a costs a bag of money.The idea was to heat a small amount of water instead of the tank,which immediately circulates in the indoor's heat exchanger.I made a quick test and some measurements and math,but i'll post them later together with some pictures,because i must go out in couple of minutes
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Old 01-16-19, 12:13 PM   #15
pavel
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Hi, just a small advice to the controller: for my DIY GWHP I run main controller process and management web console on NanoPi Duo board, which is Linux capable small board for few bucks. The software is written in Node.js, so it's relatively easy to write even complex asynchronous algorithms. NanoPi Duo is then connected by I2C bus to all the peripherals:
- compressor replay
- compressor soft starter SSR
- EEV controller
- temperature, pressure and flow sensors
those peripherals are implemented in C++ on STM32F030 Cortex-M0 MCU.
If you are interested, just let me know.

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