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Thread: microcontroller controlled. DIY HVAC retrofit??

  1. #1
    Variable Bitrate
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    microcontroller controlled. DIY HVAC retrofit??

    hello forum. i know, that stuff like that has been done before, using fusion brain or other microcontrollers, since i have seen some scattered posts..
    what i want to do, is make a HVAC system for my car, that will be controlled by an arduino, (prety much same as with fusion brain), and from there, i will contrroll the arduino via my carpc...
    the main problem is, my car does not have any AC at all.. it has an ancient, heated blower, that dosent even work so well.... so i am guessing, my best option would be to get rid of everything, and build a new system using other car parts... (vents, and everything)

    Could someone share some detialed info, on the varius parts needed,for a HVAC system??
    any previus expariance would be helpfull as well

    1)so far i have "Figured" , that i should use a servo, to controll, which vents get the air,
    2)controll the blower, via a PWM (i think so at least)

    but as for how to set the temperature, and what parts are needed for this job, i have no idea... :/
    edit: to heat the air, coolant from the engine is used?? this is true for newer cars as well??it seems prety primitive....
    Last edited by settra; 03-21-2014 at 06:56 AM.

  2. #2
    Raw Wave
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    Primitive? How so? There is so much heat generated as a byproduct of internal combustion, why not use it? Essentially it is free heating.


    I'd suggest you establish what AC etc you are going to fit - the compressor, cores, console, fans, and integration into the heating, etc - at least then you know what hardware you need to control, and how.

  3. #3
    Variable Bitrate
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    Quote Originally Posted by OldSpark View Post
    Primitive? How so? There is so much heat generated as a byproduct of internal combustion, why not use it? Essentially it is free heating.
    well yea , i agree on that. the only problem i can find, (and maybe it is so, because, that is what happens on my car) the engine coolant takes allot of time to heat up (certainly more than 10minutes), so the most days i use the car, i end up, just being cold ....

    so from what i hava found , all the magic, happens inside the HVAC "module assembly" or whatever. mine, either has space for the AC evaporator, or it dosent.... (my car model had versions with AC, so compressor and other parts, i could use from that).
    I think it works like that : (correct me if i am wrong) , 1) if you press the AC button (what does it ACTUALLY do? ) , the evaporator, (or AC radiator) gets cold.
    2) the air blower blows air, that passes from the evaporator, which makes the air Dry, and cold
    3) when you select how much heat you want, you actually open a valve, that lets coolant from the engine , to go through the heat core. so when the cold air passes from it, it becomes hot, and so you have your nice dry heat..

    so, in order to controll all that from the PC, you have to take control of:
    1)the motor blower (Easy)
    2)the AC button (i know it somehow turns on the air condition, but how?? the compressor is anyway always connected to the engine pulley...)
    3) use a servo, or a steper motor, to open or close, the valve that allows coolant to pass the heat core... is the thing that does that, called "actuator"??
    4) use another servo to control the air direction vents...
    3-4 and could be very strong servos, if the cars vantilation was designed with manual turning knobs...

    finally i was thinking: is there something like a "electric heated core", that you could use besides the "coolant" one, so you could get hot air, even if the car has just started?
    (in the microcontroller, this could be done by something like monitoring the engine temp, or use a raw "in the first 10minutes of run "

  4. #4
    Constant Bitrate
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    i lost my answer . i ll write it again .

    my car has a heater that fits all vw vehicles in north europe. it is an expensive part ( around 600 euros) and it is below the vehicle. on the other hand you could use a silicon rubber heater.

    both of them ( silicon and the aux. heater that i mentioned befoore ) consumes enough amps.

    here you can get an idea
    Last edited by Happy_Feet; 03-22-2014 at 05:23 AM.

  5. #5
    Variable Bitrate
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    the aux heater, heats water?? i was thinking more of something ,that heats itself (like a coil or something) and then , the air passes through it...
    what are the silicon rubbers?

  6. #6
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    in my car this heats the water so the engine would warm up in seconds. so the whole engine gets hot enough in less than 2minutes so the air coming from the engine is warm enough .

    the silicon rubber heater ( sorry for these guys -- αντισταση σιλικονης ) is a flexible resistance . i used that to build a egg hatching machine ( κλωσσομηχανη) .

    of course due to my poor knowledges these are what i understand. perhaps someone can explain better.

  7. #7
    Variable Bitrate
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    i see. but that way, the water heater, serves a whole other propuse

    well actually, what i am looking for, seems to actually be a thing : http://www.ebay.co.uk/itm/VW-AUDI-SK...item43c642a0d6

    serves the exact same propose with the heated core, but only difference, is it does it with electricity... but i am guessing the amps required for that thing to work, will be great, so its best to install both the coolant driven, and the electricity driven cores, IF (And that is a big IF) , there is enough space...
    that way, you could controll them like that :

    have a thermometer, that measures the temp, of the outgoing air.
    set a desired temperature, like 28 celcius.

    then, the microcontroller starts with, opening full the coolant valve. after some time, if the air is not hot enough, it start , applying voltage to the electric core.. when the temp gets more than the desired, it lowers the voltage of the electric core, and if its down to zero, it starts to close the valve...

    OF COURSE, you could go ahead and remove the coolant one all together... that might be ok, for a casual car, but pretty much, on all our cars, Amps are precious, so i dont know if its "fine" to spend them on heating... :P

  8. #8
    Raw Wave
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    The AC switch engages an electric clutch that spins the compressor. It's a typical 'split' compressor fridge or aircon system - condensor in front of the radiator; evaporator in - or ducted into - the cabin.
    There are various interlocks - eg, economy settings; clutch disengages if the cabin fan is off and maybe during idle else idle speed increases with aircon on, etc.
    Just google car aircon and you should find suitable descriptions.


    As to the initial cold, heaters are usually taken from the head before the (mechanical) thermostat so warmth should be evident within 1 minute, maybe 2.
    In colder places, plug-in warmers are common. Usually OEM is a sump oil heater whereas DIY add ons comprise a short tube with heater that is inserted in the lower radiator hose. These are powered from domestic AC supplies and are usually timer set (ie, to come on maybe 60 minutes before driving).
    And there are also the auto systems - those that run the engine when cabin temperature drops below some limit. (They can scare the crap out of you when, er, communicating with your partner on the bonnet in some dark snow covered carpark.)

    Many people use 12V hairdryers in their demister ducts for faster defogging, tho aircons are far more effective at demisting and probably quicker.

    Electricity for long term heating simply isn't viable. Not only might a typical 2.4kW local AC heater NOT be anywhere near enough to warm a typical cabin, but that heater alone would require over 200 Amps @12V. Plus it would suck over 4HP from the engine.
    Compare that to water/coolant that can easily provide 10kW or more of heating without effecting engine power of fuel economy.

  9. #9
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    mmm. i didint realised that an electric heater core, would suck SO many amps (i though something about 20 - 30A). but if this is the case, then i guess i should find something smaller, to use only untill the water gets hotter......
    a hair dryer is indeed a nice idea.. or something else that is small and gets hot :P

    so appart from the AUX heater, i still will need two servos, to move the mechanical parts... (air direction, and the coolant valve) (my car dosent have the option for recirculated air), any idea what torque should i look for??

  10. #10
    Variable Bitrate
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    so, as i sed , my car does not have the option, to choose, between recycling the cabin air, or drawing from the outside....
    i guess, for efficient heating, (And cooling), when the engine starts, it would make large difference, if it could just recycle the air from the cabin... correct??.. (Correct me if i am wrong).

    so i was thinking this: my "air condition air intake" is in the engine compartment, just bellow the windshield... i could, make an assembly , that fits directly on it, and has two large tubes for incoming air.. the one will suck air from the enviroment. for the other, i will have to cut a hole, that gets inside the cabin. i will pass the tube though that whole, so that it sucks the air, somewhere near the passengers feet.... so i have two questions:
    1) does this make any sense on doing, or am i talking crap? :P is there any point on doing it??
    2) in order for it to work, i would have to install something like a "Flow direction electric valve"... or something.... any idea, what item could do that job??

    i realize that this is a bit of topic, but with any luck, i might get some help on what to do

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