Results 1 to 4 of 4
  1. #1
    Join Date
    Feb 2014
    Location
    Davis, CA
    Age
    34
    Posts
    2
    Rep Power
    0

    Question Pedal powered compressor



    Hi all,

    I'm not an expert on this topic but I have an idea for a hobby project that I hoped I could get some feedback on here.

    I'm interested in trying to make a pedal-powered ice-cream-and-frozen-drink maker that runs a compressor directly. I'd like to know the feasibility of this. Some back-of the envelope calculations:

    - A typical biker can put out about 200 watts (~1/4 hp) continuously
    - I'd be aiming to cool about 1 quart of liquid from room temperature to frozen. Given the specific heat and heat of fusion of water, this amounts to change of energy of 120 Watt-hours.
    - If the coefficient of performance of the system is 2, then one should be able to cool the liquid in about 20 minutes (120 W-h/ (2* 200 W)).

    So this seems theoretically possible, but one would need a compressor and refrigerant system that fits the bill. It would have to be a compressor that could be efficient when run by an external belt/crank giving about 1/4 HP. One can use gearing to increase RPM, but it would be best if the RPM required were < 2000 RPM. And the refrigerant should evaporate at a below-freezing temperature.

    Main questions:
    - I'm sure I'm missing some major considerations - what are they?
    - What compressor would fit this bill? I thought that maybe something designed for A/C of compact car might do. As far as I can tell, all compressors designed for small fridges (or countertop ice cream machines) are hermetically sealed combined motor/compressor units.
    - What refrigerant would make sense? If this could be done with propane, it would make the DIY aspect easier.

    Thanks for your help!



  2. #2
    Join Date
    Jul 2010
    Location
    NTH.QLD Australia
    Age
    55
    Posts
    1,755
    Rep Power
    26

    Re: Pedal powered compressor

    "Legging it" has taken on a new meaning in this post.
    If i had to provide stable cooling in your situation, i would use a 300 Amp/Hour battery to power a Danfoss 12/24 DC compressor and top up the battery by leg power.... driving an old 35 amp vehicle alternator.
    That way you can take a break to catch your breath.
    To the optimist, the glass is half full. To the pessimist, the glass is half empty.

  3. #3
    Brian_UK's Avatar
    Brian_UK is offline Moderator I am starting to push the Mods: of RE Site Moderator : and general nice guy
    Join Date
    Mar 2001
    Location
    Dorset
    Age
    69
    Posts
    10,441
    Rep Power
    50

    Re: Pedal powered compressor

    Don't forget that you also need to power a condenser as well.
    Brian - Newton Abbot, Devon, UK
    Retired March 2015
    Please support http://the100project.net/Home

  4. #4
    Join Date
    Feb 2014
    Location
    Davis, CA
    Age
    34
    Posts
    2
    Rep Power
    0

    Re: Pedal powered compressor

    Could the condenser be passive? That is, just a set of coils that the refrigerant passes through with a lot of surface area? I suppose a small mechanical fan blowing air over the coils would boost the efficiency a lot without a lot of additional effort for the biker.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •