anyone tried 'seawater' cooled Air Conditioning?

Discussion in 'Boat Design' started by Squidly-Diddly, Dec 16, 2013.

  1. Squidly-Diddly
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    Squidly-Diddly Senior Member

    As was mentioned in recent MacGregor thread, AC takes a lot of juice, more than a outboard's alt will be able to supply.

    But even when air is 100 deg F, water tends to be much cooler, even chilly, especially a few feet down.

    Use small electric fan on a radiator, and maybe a small pump to operate it when stopped.,
     
  2. fredrosse
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    fredrosse USACE Steam

    Sea Water Tempwrature

    There are many instances where surface water temp is fairly cool, and could provide some level of air conditioning, but one would need fairly large heat exchanger surface to get the level of air cooling to reach human comfort criteria.

    Sea water temperature takes a big reduction a couple of hundred feet below water surface, far too deep for a practical air cooling system.
     
  3. waikikin
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    waikikin Senior Member

    The building at my work has seawater cooling/ac, & some small "air" split systems for isolated workshops.
    Jeff.
     
  4. CDK
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    CDK retired engineer

    What you need to reduce the cabin temperature is called "delta-t", the difference between two temperatures. Although it may feel chilly if you jump in, seawater around a boat doesn't qualify.

    If the power to run a compressor is not available, the only option is to evaporate water using a fan and a piece of wet fabric like a towel. There are also commercial units on the market using that principle. In absolute terms their performance is not impressive, but even a difference of 10-15 degrees is felt as comfortable on a hot day.
     
  5. FAST FRED
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    FAST FRED Senior Member

    Many folks in the hot areas will button up the boat at sundown and hose the cabin top and decks too remove as much of the daily heat from the sun with sea water.

    Then the boat is opened up , and the sea water temp is achieved below decks for night sleeping.
     
  6. PAR
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    PAR Yacht Designer/Builder

    This is a fairly common thing in the poor ends of the tropics and we call it a swamp cooler. A small pump is connected to a hose, to pickup sea water. The inlet usually has a "J" fitting, weight and possibly a float to hold it just off the bottom (a foot or two). This water is brought aboard and run through baseboard heater pipes, usually arranged in a ring around the top of the cabin walls. The really clever guys will encase these and use small pancake fans to easily blow air across the base board tubing. It works, require very little energy and can make a significant temperature difference, though you're still stuck with the humidity. Most use a 10' to 15' hose, as it's quite shallow here, but 10' down it's usually a lot better then the 98+ in the surface air.
     
  7. jonr
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    jonr Senior Member

    Search for "fan coil" if you want a radiator with a built-in fan (preferably multi-speed). Make sure it has a drain tray (for condensation).
     
    Last edited: Dec 18, 2013
  8. PAR
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    PAR Yacht Designer/Builder

    A typical fan coil will have a much higher electrical load than a swamp cooler and damn noisy too. I've never seen a relativity soft spoken fan coil.
     
  9. frank smith
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    frank smith Senior Member

    How about a old window air conditioner with the the compresses removed, and a couple of small wisper fans. You could experiment with the condenser or the cold air side. I think that might offer the best rate of heat exchange. and cost net to nothing . Hooked up to a wave pump , the fans could be driven by a solar cell array.
     
  10. PAR
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    PAR Yacht Designer/Builder

    Evaporator coils require a lot of air pushed through them if using just water as the refrigerant. You'd be much better off using the condenser coil in this regard. In both cases you now have a big hunk of coils and a noisy fan to contend with, which might not be desirable and electrical load will still be much higher then a handful of 3" pancake fans blowing across a linear baseboard tube.
     
  11. CDK
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    CDK retired engineer

    Spent my honeymoon in July nearly 50 years ago in Tunisia. The seaside "luxury" hotel had large central heating radiators in the lobby and dining room, mounted against the ceiling. Seawater was pumped up 24/7 from the beach at a depth of at least 30 ft.

    So I have first hand experience: it does not work!
     
  12. PAR
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    PAR Yacht Designer/Builder

    The key to making this type of system work is two fold. The first is obvious, the space needs to be tight, but the second and where most fail is the volume of air across the coils has to be relatively low.
     
  13. frank smith
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    frank smith Senior Member

    Par, right about low air volume. Pan cake fans like for cooling electronics I assume. Where would you mount it? I supposes it could be inside, but I think you would want some fresh air in the mix. Or would it be roof mounted over a hatch?
     
  14. PAR
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    PAR Yacht Designer/Builder

    The good ones build a rectangular box the length of the base board heater core, which is usually in 8' lengths, though can be cut or soldered to length. The fans are used two different ways, the most common is blowing air into the ends, across the fins to a centrally located vent. Another setup I've seen is fans located at the vent, sucking air in the ends. I wouldn't want to speculate as to which works best, but the fans at the vent seem to direct air better.

    Picture a 8' long 3"x4" plywood box, with the core suspended inside, usually on a few "L" brackets and a 3"x6" vent, mid way down the length of this box. Not a lot of noise, not a lot of cooling, but decidedly a noticeable temperature drop, if you keep the boat closed up.
     

  15. Nate57
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    Nate57 Junior Member

    Was sitting in a tropical bar one day with screened windows when the bartender decided to wash the screens by spraying them (from them inside) with a garden hose. What with a stiff breeze the result was an immediate reduction of interior temp of seemingly 20 degs. F. This was what I've heard of as the swamp cooler effect. The latent heat of evaporation transferring the heat or some such (my reefer prof would scold me). Shortly thereafter I experimented by sewing bug screen into the mouth of the wind scoop on my foc'sle hatch. Never got around to installing a small seawater pump and mister but by simply using a spray bottle it achieved fairly impressive results.
     
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