holy grail solar air conditioning unit that isnt powered by honda generators and is

Discussion in 'Boat Design' started by hoytedow, Mar 12, 2012.

  1. WestVanHan
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    WestVanHan Not a Senior Member

    So then why don't you?
     
  2. ImaginaryNumber
    Joined: May 2009
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    ImaginaryNumber Imaginary Member

    I'm puzzled by these numbers. In the US PEX (or polyethylene) pipe/tubing is very commonly used for water transport. It probably isn't as flexible as rubber hose, but its density is just a bit less than water. So its weight hanging over the side of a boat should be close to zero. In fact you might need to weight it to get it to hang where you want it to.

    (Recent comments notwithstanding, thank you for your MANY informative and COURTEOUS posts)
     
  3. Nick.K
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    Nick.K Senior Member

    Always impeccable!
    Many thanks Daiquiri for your kind replies to my threads and many other interesting posts.
    Nick.
     
  4. daiquiri
    Joined: May 2004
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    daiquiri Engineering and Design

    Thank you for the last part of the post, very kind of you. :)

    In fact, you are correct about the weight issue... I had taken that hose as an example, which is actually a high-density hose (1750 kg/cu.m, vs 1025 kg/cu.m of the sea water), giving a total weight of 95 kg. One can as well choose this type of hose, which is much lighter, just 550 kg/cu.m, or 0.15 kg/m: http://www.hosecraftusa.com/model/PM1_Multipurpose_PVC_Hose . By the way, it comes in 500 ft reels (which weighs 23 kg), just what we need. :)

    It floats on the sea surface, as you have noted, and would require a weight to make it sink to the required depth. The buoyancy will try to lift this hose up with 42 kgf of force, so there will be a net upwards force of 19 kgf, and that's a minimum ballast weight necessary. The actual additional weight will have to be at least 20-30% bigger, around 25 kg, in order to give it a reasonable descent speed in the final moments. I say that 5 minutes (pretty long, imho) is maximum allowable time for the hose to fully extend, which mean that an average descent speed of 30 m/min is required, or 0.5 m/s.

    So we end up with around 50 kg of the hose+weight. Ah, I've discovered that reels are pretty heavy - 30 kg: http://reelcraft.thomasnet.com/item...atile-configurations-series-30000-/ca32128-l? , which is nearly double my first estimate. So at the end, the hose + reel won't be 130 kg if we choose this type of hose, it will be around 80 kg, plus all the rest of the pumping system (pump, piping, filters, heat exchanger, PV panels, batteries, charge regulators, wiring).

    Cheers
     
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  5. vadim_go
    Joined: Jan 2012
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    vadim_go Junior Member

    Interesting idea.
    How often do you guys anchor in more than 20-30 m? What is the temp of the water at the bottom of the usual anchorage?
    And what is the temp/humidity on the average day you sleep on the boat?
    Because if it is a sunny day with a dry breeze, even dousing the deck from the bucket will help. However, a steamy night around here (I would say, from Boston at least all the way south), you need to fight both the temp and the humidity. If we stay with the usual way, energy is used to pump a cooling medium outside, circulate the chilled/dried air inside and to pump the stuff that transfers the energy in between (freon or what's the name, excuse my lack of pro-knowledge). I think, by increasing the size of the coil, either one of the inside-outside units could be powerless. Is there a way to get rid of the compressor that is I believe the biggest energy consumer in AC system? Are there any compressor-less AC at least in theory?
     
  6. CatBuilder

    CatBuilder Previous Member

    This is the ticket to compressorless air conditioning...

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

    Unfortunately, they have not made one the right size for smaller boats.
     
  7. WestVanHan
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    WestVanHan Not a Senior Member

    I looked into Peltier modules-forget it.

    And there's that fridge that runs off of 140 decibel sound waves.
     
  8. Submarine Tom

    Submarine Tom Previous Member

    Hoyte,

    Great idea, great thread.

    Delta t is all it takes.

    You got it man.

    Good on ya!

    -Tom
     
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  9. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    LOL, right... Personally, never.

    If you want to keep it as simple as possible, ancient Egyptians had a method which worked: http://inexpensivehomebuilding.blogspot.com/2007/04/ancient-egyptian-air-conditioner-cheops.html :)
    A modern version of this system is done with water-spray nozzles. However, evaporative cooling works well only if the air humidity is below 50-60% at 35°C or blow 40-50% at 30°C. Otherwise it is not very effective. At 35 °C and 60% the improvement of human comfort with evaporative cooling is questionable. See the attached chart, with colors indicating the level of human comfort (green = ok, red = too hot, blue = too cold):
    Comfort.jpg
    It shows how small is the improvement when evaporative cooling is done, for example, at 35 °C and 60% relative humidity (upper arrow). you end up from red zone to another red zone. Much better when done at 35 °C and 40% RH (lower arrow).

    Some other creative ways to achieve air conditioning are mentioned in this site: http://www.builditsolar.com/Projects/Cooling/passive_cooling.htm . Whether they, and which of them, are applicable to boats is yet another question... :)

    Another possibility, but not on small boats, is the use of absorbtion chillers, like the ones CatBuilder has pointed to. It has been discussed here: http://www.boatdesign.net/forums/bo...tioner-sun-holy-grail-42158-8.html#post538274 and the included example shows why these machines are not suitable for small vessels (see the weight and dimensions).

    Cheers
     
  10. Brian@BNE
    Joined: Jan 2010
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    Brian@BNE Senior Member

    Another issue to consider is thermal conductivity of hose. You need something that isn't going to shed your thermal benefits on the way up.

    Thanks Daiquiri, your manners always impeccable and effort from pro's like you always add value to the threads.
     
  11. daiquiri
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Very correct. So again a more thick and heavy rubber hose (like the type in my post #5) becomes interesting, if one wants to avoid pumping water at too high speed (which would mean significantly increasing the electric power required by the pump).

    Whichever way one pulls the blanket, it's always too short. :)
     
  12. nimblemotors
    Joined: Jun 2009
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    nimblemotors Senior Member

    At the 2007 TED Conference, Adam Grosser presented his research of a new, very small, "intermittent absorption" vaccine refrigeration unit for use in third world countries. The refrigerator is a small unit placed over a campfire, that can later be used to cool 3 gallons of water to just above freezing for 24 hours in a 30 degree Celsius environment.[6]

    Hmm, doesn't sound too big for a boat.

    Another thought might be to use a batch process instead of a continuous, where you "store" the cold via a compressed gas and uncompress it to release the cold during the afternoon. how much can be stored and its weight I leave to the "physics" people to shoot down.

    I agree that humidity is actually a worse condition that heat in comfort and in tropical climates would be a bigger issue.
     
  13. troy2000
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    troy2000 Senior Member

    I'm surprised PAR hasn't weighed in. I don't remember whether it was in PM's or in posts, but in the past he's mentioned a method of cooling that he uses (while anchored, I assume). He suggests dropping a hose overboard and down to deeper and cooler water, and using a 12v pump to run it through a radiator. Put a 12v fan behind the radiator, and you're circulating enough cool air to make a difference, even in Florida.
     
  14. Submarine Tom

    Submarine Tom Previous Member

    Delta t!

    -Tom
     

  15. Jeremy Harris
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    Jeremy Harris Senior Member

    I stayed off this thread after my initial response because it seemed one (fairly new) member was intent on just trolling and being insulting to all and sundry, which was a shame, as this is a good topic.

    The relatively high sea temp in mid summer was cited earlier as the reason not to use near-surface water for cabin cooling, which is a good point but missed what I was aiming at doing. Much of the cabin heat comes from the roof of the cabin and the decks being heated to pretty high temperatures by the sun, often these will get over 60 to 70 deg C, enough to almost burn skin. If these radiating surfaces can be cooled down, even to just 30 deg C, then the heat input to the cabin would be reduced a fair bit. I know that 30 deg C is still uncomfortable, but it would be an improvement all the same. It would take little in terms of equipment and added weight to make such a simple system work.

    The additional cooling load then becomes less demanding, such that any AC type system has less work to do when it is really hot. Absorption refrigeration can be made to work OK with a solar collector and concentrator, and although not very efficient as a heat pump, if combined with sea water cooling for the condenser (maybe the comfort cooling water exhaust flow) it might be able to cope with the reduced load imposed by a cabin that's already been cooled to some degree.
     
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