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  1. #1
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    Micro Air Conditioner for Motorcycle or mobile applications

    Hello Everyone this is my first post. I'm an Electrical Engineer, with some background in thermodynamics I guess.

    My Experience with A/C is minimal. I understand the basics, I know how the systems work, about energy transfer, phase change and so on. I've been lurking in this forum as well as the OverClocker Forums where people superfreeze their CPU's. It seems they have a lot of knowledge in the small a/c field, but my project has nothing to do with PC's.

    I'm planning on making a small air conditioner that will ride in the back of a scooter or motorcycle. It may not be as impossible as it seems due to today's advances in technology. I've been thinking of this for a few years and finally have some budget to try it out. There are many parts of this project, most of which I can handle.

    The structural part is Easy. The electrical part for me is easy since I can program and build dedicated electronics and monitoring. The power will be delivered by a batterypack or from the motorcycle if its large enough ( like one of those ADV rider style BMW bikes. The total power consumption should be about 150 watts

    I've calculated that the average Human needs about 400BTU's of cooling, and while outside in the sun, maybe more. This adds up to 115 to 200 watts of cooling? Correct me if I'm wrong. The design I had in mind can cool up to 400 watts max, so this range should be possible (300-500btu)

    For a compressor, I'm looking at these :
    http://www.aspencompressor.com/products/


    Or more likely this one since is cheaper:
    http://r.ebay.com/wptYdE


    They can provide up to 400 watts of cooling according to their COP.

    For condenser, I need the smallest possible due to limits of space, so I'm looking at something like these pictures:




    They are used for Overclocking computers. While their power handling is small, I've heard of them handling about 200 watts. Also, I will use a motorcycle fan, which can move air in magnitudes much larger than any PC fan ever can + wind flow as the vehicle moves.

    For Evaporator...I'm stuck. I'll either have to make my own, or use come type of cold plate and attach a heat sink where air will flow. Something like this:

    A Shorter version of this attached to a heatsink
    [IMG]www.imgur.com/Uh2zSUI[/IMG]



    Or a modified version of these where I may replace the heat pipes with my own copper pipes:





    some of the small compressors have a dryer in the line some of them require it to be added. Due to space limitations, I'm wondering what type should I get, or if I need a receiver( holds liquid and cleans it before capillary)/ suction holder? ( stops fluid from coming back to compressor?) since the unit will move about quite a bit.

    Also I'm completely lost as to what capillary tube to get, or expansion valve. I have 0 clue. I would just buy some different ones and guess, but they say 6-10 feet of this stuff. Even if I coil it around I dont know where I will fit it. maybe expansion valve is better for me.

    For Gas, I think I will go with Propane, or R134. I know the capillary and exp are different for gas as well as pressures, but The main point is that propane is easy, cheap and readily available everywhere, environmentally friendly, and comes with its own smell which is good for detecting leaks, or in case the leak is in the evaporator and the person using the unit can smell it.

    The fan for the condenser, duct works, air jacket for the person, etc are somewhat irrelevant. There is hundreds of pre-made applications I dont even need to design anything. Many off the shelf components for this section.


    Thanks to everyone in advance for any suggestions.

  2. Likes cikgunas, DavidDeBord, dart289 liked this post
  3. #2
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    This is the cold plate, I messed up the link and can't fix it because I can't find a way to edit my post:
    [IMG]www.imgur.com/Uh2zSUl[/IMG]

  4. #3
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    There are already motorcycle rider air conditioners available. They utilize solid state technology. How do I know? Your question prompted me to think that maybe solid state would be preferable, so I googled it. Actually, I used Bing. Searched "solid state air conditioning, motorcycle rider". Looked at the first of 4-5 promising looking results. Very interesting stuff. Too pricy for me, though. The whole idea doesn't seem feasible to me. Much, if not most of the heat discomfort when riding is when I'm dressed for the ride, but not moving, and even when not on the bike. Not to mention not wanting to be tethered to it.
    I realize that doesn't answer your question, but it may shed some insight as to why there has been an apparent lack of motivation to create one, or to market it well, considering that I just found out such a thing already exists.
    However, you've got my curiosity up, so I may chime in if I think of something. Good Luck!

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  6. #4
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    What is the purpose of the Clear RTV cement on the two copper lines by the condensor coil in the photo with the red hose ?

  7. #5
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    I've known about that motorcycle a/c. But solid state is 40% efficient at best. I would need 400 watts or more, which is crazy. And 1,500 I can build a few of those myself. I want to build it because of the challenge i guess.

    And the RTV? I guess it was meant to hold panels and things. What you see in that picture is the inside of what used to be a larger box unit.

  8. #6
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    Quote Originally Posted by Joel_Dude1450 View Post
    I've known about that motorcycle a/c. But solid state is 40% efficient at best. I would need 400 watts or more, which is crazy. And 1,500 I can build a few of those myself. I want to build it because of the challenge i guess.
    I can understand that.

    You may want to start with researching the electrical output ratings of bike alternators. That could give you an idea of how feasible your target energy usage is.

  9. #7
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    Steer clear of propane. Use either a piston or another form of mechanical metering device (ball valve maybe considering simplicity and price with this being your prototype) instead of the cap tube you purposed. Don't use a compressor just because it is cheaper unless you know is of quality. I suggest you start with a single speed compressor and one you prove the design maybe you can expand and investigate using variable drive. You could possibly mount the condenser to the exit side of the radiator. You may also want to reconsider your refrigerant choice depending on the design pressure of your system in regard to capacity and refrigerant heat capacity. I think a heart sink on the condenser is a good idea but my suggestion is to investigate mounting it on our around the existing cooling system. This could be more difficult depending on the manufacturer but it could also help simplify a large part of your design.

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  11. #8
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    Thanks to everyone for your input and ideas:
    The power supply needed is anywhere from 100-150 watts. Most small bikes cannot provide that, only large touring bikes have the extra wattage available. I will make a battery pack with 18650 batteries( laptop batteries) and it will last about 1 hr. It will also have a input if the bike owner desires to power it himself by any other means (12V).

    I like the idea of not using capillary tubes since I have no clue what to do with them or how to use them. I guess expansion valve would be better for this situation. Maybe have the liquid go into a receiver/dryer where it can be stored while its used? the only problem I see with this is that the coolant gas has to go up and down several times so I want to avoid that. I dont know yet.

    Piston or ball valve for metering? I've never heard of it for refrigeration, I'll have to investigate. I'll have to use R134, its readily avialable everywhere, cheap and the compressors I'm looking at are rated for that so I'll go with the flow, and those little guys can't do propane :'(

    I see your ideas for the mounting in the vehicle. The idea is that this is a self contained object that can be installed or removed without any mods to the motorcycle/scoot. some bikes are air cooled so they dont have radiators to mount on, or fans. Essentially, I can't rely on the vehicle at all to provide anything for the unit. This way it is more self-sustaining and easier to apply to a broad range of applications.

    I like the HeatSink condenser idea too, my company had these cold plates made a long time ago, its basically a copper pipe running trough a aluminum plate.



    I can then use a smaller plate and a heatsink, completely isolating the user from the gas side. The problem is finding a custom made plate, and since some heatsinks already have copper pipes running trough, then why not replace them with real gas lines? We'll see.

    The motor comes with a variable drive system, is not optional! but it can be fixed at a certain rpm. here is my question: would a variable RPM compressor be able to make different pressures? this would be useful to control the heat transfer, temperatures and whatnot right?

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  13. #9
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    A friend and my self have worked on this idea for years (we were both long distant motorcycle riders).
    Basically found that mechanical stuff ended up too expensive for the motorcyclist.
    Our rig we made for "sidecars" was basically an ice chest with a 12v pump with hoses to a fan/coil in the hack.
    And hoses to a cool vest for others.
    Worked across 2 gas stops +. Then it cost a bag of ice.
    The design cost was very expensive....... Beer
    Life is too short, Behappy!
    TFMM

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  15. #10
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    Figuring out the compressor & condenser will be relatively easy compared to the evaporator.

    behappy has given you a clue...... Water works.
    My suggestion would be to refrigerate a water solution (with an appropriate level of anti freeze) in a reservoir that had a pump to circulate this solution to a vest.



    Here's an example of what's now available on the market.... http://www.veskimo.com/

    Also here's some DIY discussion...... http://www.bmwlt.com/forums/riders-g...ling-vest.html

    Good luck in your endeavor & if you need someone to demo your products look me up.
    I'm a rider and I Hate the heat and dress for the fall, not the Summer. (Play on words/full gear all the time).
    Living in SoCal, I could almost test year round
    Eric

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  17. #11
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  19. #12
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    I prefer air because it will never leak. It weights nothing, is super simple to implement due to many vented vest in the market, cheaper to make, easier to attach-detach from device, can be folded to take no space, it can work even with leaks,

  20. #13
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    I have a question I need help with, I was reading about expansion valves(XPV), Orifice tubes and capillary tubes:

    1)XPV: mechanical device controls flow of refrigerant with a bulb and diaphragm.
    2) Capillary tube: The smaller and longer, the more restriction.
    3) Orifice tube: Same as CapTube except these are small and short. Used for car a/c

    I was using some calculators online and they gave lengths of 3-6 meters for some capillary tubes, yet smaller ones where about 11 inches. A Orifice tube is a mere 3 inches long, the tube itself inside is like 1 inch long. A XPV is literally like 1 inch long.

    For this application, I'm guessing a maximum temperature for the liquid after the condenser to be 110F and I want the air going out of the evaporator to be 80F ( 75 if possible). The compressor runs about 2.8cc of displacement, capacity up to 500W cooling, I will use 134a. here is the compressor specs ( they are close to the one I want to buy)



    So here are my questions:
    1) Would a capillary tube of small diameter be the same as a long one with larger diameter? Is there a drawback to doing this( using a really small/short one)?
    2) Can I just use a orifice tube from a car? ( I suspect they are a capillary tube with very small diameter so its really short) I can modify them, or integrate them into the system)
    3) Is there any useful XPV that I can use for this application or should I avoid them? if I use a XPV do I need a receiver after the condenser?
    4) The compressor has variable speed. Can I use this speed control to control the head pressure/ condenser temps,/ cooling temp/ etc ( I guess its all related)

    I know that the answers might be vague or incomplete, since I dont have all the information now and they all depends on variables, but any help is greatly appreciated.

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