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  1. #1

    I'm not a Hvac guy, but,

    I want to use high pressure refrigerant as steam, to run a compressor (backwards) to run a generator. (to run my house, or charge a battery pack)
    Is there anyway to match all of this together? What rating on the compressor would tell me that its strong enough to run a (say) 20hp generator?
    I want to put the refrigerant steam into the drive side of the compressor to subsequently run the generator. How much pressure out of how large a line will turn the right size compressor.
    I'm sure this is not a normal question. Its diffinently in the DIY area. And, probably no one has all the answers, but I would appreciate any answer, even a pretty good guess, to help me get started.
    Thank you,
    Clockou

  2. #2
    Join Date
    Dec 2001
    Location
    Ocean Pines, MD
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    7,033
    Not a DIY site, especially not for a wonderment like this idea.

  3. #3
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    I'm not sure what refrigerant you are planning to use as the "steam", or how you would go about modifying a compressor to act as a "steam" engine to drive your generator, but if you are planning on driving a 20 hp load with it, the quantity of refrigerant "steam" needed would be huge, as would the size of the compressor.

    Even if you somehow managed to create a device that is fairly mechanically efficient, with a closed loop system, the energy requirement to cool and condense the refrigerant "steam" back to a liquid for reuse would exceed the output of the generator. No free lunch in the cold harsh reality of physics.

    If your idea is to operate the refrigerant "steam" side as an open loop system, that would be highly illegal with most chemicals used as refrigerants. The refrigerant cost would also greatly exceed the fuel cost of a conventional generator.
    If more government is the answer, then it's a really stupid question.

  4. #4
    Join Date
    Jul 2009
    Location
    Plant City, Florida
    Posts
    2,198
    Quote Originally Posted by clockou View Post
    I want to use high pressure refrigerant as steam, to run a compressor (backwards) to run a generator. (to run my house, or charge a battery pack)
    Is there anyway to match all of this together? What rating on the compressor would tell me that its strong enough to run a (say) 20hp generator?
    I want to put the refrigerant steam into the drive side of the compressor to subsequently run the generator. How much pressure out of how large a line will turn the right size compressor.
    I'm sure this is not a normal question. Its diffinently in the DIY area. And, probably no one has all the answers, but I would appreciate any answer, even a pretty good guess, to help me get started.
    Thank you,
    Clockou
    Instead of reinventing the wheel, why not get a Solar PV Panel to charge your batteries and a generator?

  5. #5
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,479
    Google "Refrigerant Steam Engines". Surprisingly, there's a lot of discussion going on out there. Mostly "pie in the sky" stuff, but a few thought provoking ones.

    I particularly like this one where it talks about using scroll compressors:
    http://www.redrok.com/engine.htm

    Theoretically, I suppose it's possible. Using a refrigerant instead of water allows for the the boiling of the refrigerant to create high pressure "steam" utilizing a relative low temperature heat source and condensing it with a cool medium as a heat sink.

    However, to attempt to build such a machine using a device designed as a refrigeration compressor would appear to have far too many stumbling block to be even remotely practical.

    In any case, you won't get much detailed help here...even if there is someone familiar with such applications...because this site doesn't allow such discussion in an open forum.

  6. #6
    Join Date
    Mar 2003
    Posts
    7,326
    Honestly, I doubt a compressor as manufactured today would do it. There is too much restriction to be efficient, think discharge and suction valves. What you would need is one with no valve plates, and a way to control the "steam" flow. the least amount of resistance to flow would be best to spin your generator. to me, a centrifugal type arrangement might be best as the wheels dont have high lift and spin rather freely in comparison. but then again WTF do i know?

  7. #7
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,479
    I did a little searching around and found that such "reverse compressors" already exist and are used extensively in industry. They're called "turboexpanders".

    Check out what Wikipedia says about their use in power generation applications.

    http://en.wikipedia.org/wiki/Turboexpander

    More interesting to us refrigeration guys though is how turboexpanders can also be used to replace expansion valves in a system...and generate power in the process.

    I read where a turboexpander connected to the compressor shaft can generate around 15% of the power required by the compressor.

    Cool stuff.
    Last edited by icemeister; 05-28-2010 at 05:25 PM. Reason: Ooops...Forgot to add link.

  8. #8
    Join Date
    Jan 2004
    Location
    PA
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    68,764
    Condensing back to liquid, wouldn't be that much of a problem.
    Finding a suitable compressor could be the main problem.

    But, as Stamas said, We can't help you.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #9
    Join Date
    Feb 2004
    Location
    New Mexico
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    5,723
    Turbine would be easier. And then why not just use water rather than refrigerant. But first, do the math and you'll find because of losses due to efficiency you'll have a net loss. Our electrical grid is only 32% efficient.
    Now, if you had a fast moving stream in your backyard you'd have something.
    "What Fools these mortals be"....Puck

  10. #10
    What you are describing is an ORC (Organic Rankine Cycle). It uses the same basic thermodynamic cycle as a steam powerplant (steam meaning water for the working fluid) although it uses a organic (meaning carbon in the molecule) working fluid. Some even use typical commercial refrigerants such as R134a. There have been special refrigerants that are designed specifically for ORC applications (R245FA for example).

    The cycle efficiency is dependent on the temperature gradient that you have (how cold the cold sink, or condensor, is versus how hot the heat source, or evaporator is). In very basic terms it is a refrigeration cycle in reverse. If you have a "hot source" of about 200F and a cold source of 70F (typical outside air temp) then the cycle efficiency will be somewhere around 5-6%.

    You read that right Five to Six percent efficient.

    That means that in order to generate 20 HP, you need about twenty times that from your heat source. This also means that you have to reject about nineteen times that to the cold source (this means a fairly large condensor is required).

    You could build one on your own, but it would be fairly costly and you really need to read up on it (and thermodynamics). I would suggest using a screw compressor, they have been used in some small applications as expanders. A centrifugal compressor would most likely need to be re-wheeled to be an expander (the blade angles are basically completely different, plus you need some kind of guide vane to guide the gas into the wheel). A screw compressor run backwards is much simpler.

    If you really feel the need after reading this to learn more, I would suggest RefProp, which is a thermodynamic software that can be used to design the cycle.

    Also, for those HVAC guys interested, Carrier built some small ORC's (~200 kW) using chiller parts. They are now built by UTC under the brand Pratt and Whitney (the power division). The marketing geniuses came up with the name "purecycle".

  11. #11
    Join Date
    Apr 2008
    Location
    Pluto
    Posts
    983
    Yeah yeah yeah... Keep giving him links so he can go blow himself up.
    Not as lean, not as mean, but I'm still a hardcore, ass-kicking, hard charging Marine! Oohrah!

  12. #12
    Join Date
    May 2004
    Location
    Rapid City, SD
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    7,415
    Gotta give the guy credit for thinking somewhat outside the box, it's a pretty cool idea.

    The nice thing about steam vs refrigerant though, is it's easy to generate steam with fire, and it's tough to give fire a horsepower rating, but generally fire would be easier / cheaper to create steam with vs refrigeration methods and the means to move it.

    While we can't help you (especially me, cuz I can barely wrap my brain around the refrigeration cycle when running the right way), I wish you luck if you're determined to keep pursuing this. Stay safe!
    "If you call that hard work, a koala’s life would look heroic."

  13. #13
    Join Date
    Feb 2010
    Location
    Cal
    Posts
    1,596
    It's on the market, I bought one from jc witney,It works great! 375.00 + shipping.
    I use it to power my dope grow lights and sell the remaining power back to the local utility and clear 1500 a day!

    Google "ACME perpetual motion machine". I believe Wlie E. Coyote holds the patent


    Go here for your best alternative process: http://www.toolbase.org/Technology-I...ned-heat-power
    Last edited by btuhack; 07-08-2010 at 02:04 PM.

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