how about a cheap, self contained, seawater cooled HVAC?

Discussion in 'Boat Design' started by Squidly-Diddly, Sep 10, 2016.

  1. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I've noticed even on the hottest days the water in many places is still downright cold. (West Coast of USA has the opposite of Gulf Stream, and even in the height of summer our rivers are fed by snow melt).

    Then you got the opposite. Even when the air is down way past "hard freeze" and pipes are bursting and wine and fresh meat and fruit is getting an unwanted freeze....even salty sea water barely goes below 32' F, and same with lake water below the ice.


    I'm thinking why not take a couple on automotive radiators/heater cores and a couple hoses and small pump, and maybe a solar or plug in pump and fan and get "free" HVAC.

    I'm thinking this would be mostly for when stopped and you want some AC but don't want to hear a motor, or you just don't need it enough to want to add a whole built in system, or as a "when your away" system to keep things inside from freezing hard or overheating.

    One prob for the "when your away" would be to make sure it shuts off if it starts leaking on the inside side, so it doesn't slowly but surely sink your boat over the week.

    Maybe use 'spare parts' for your existing motor/heater/AC, and some extra hose, and an extra fresh water system pump.
  2. CatrigCat
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    CatrigCat Junior Member

    I was thinking about the cheap seawater a/c but it's neither cheap nor will cool or heat the boat sufficiently. Maybe for a really hot engine room.

    First, if you don't want to sink the boat you can't pump seawater through the system. Even if you shut down the pump when there is seawater in the bilge, there will already be a lot of water damage to the interior.
    To avoid that, you will run a sealed system with a very big and very expensive keel cooler (small keel coolers won't work because of the small temperature difference).
    No more a cheap system.

    Second, seawater is not that cold during the summer.
    And if docked in a crowded marina, seawater is so warm that idling engines overheat.
    Seawater is cool when diving into but not cool enough to cool the boat's interior.
    FYI chilled water systems run at 7C. With (much) higher seawater temperatures you need a huge system to slightly cool the boat and that huge system will cost plenty.
  3. gonzo
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    gonzo Senior Member

    In the West Coast, water is usually cold, so it should work. You can simply sink a hose to pick up cold water from, preferably, below the thermocline and circulate it through a radiator with a fan behind it. They make "bus heaters" that will be good for the application.
  4. WestVanHan
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    WestVanHan Not a Senior Member

    SD: My dad did this 30 years ago when I was a kid. Basically a swamp cooler,and it worked well.
    Nowadays I can see a solar panel to run the pump,need little flow.
    I looked up SF and your August averages 15C which is 59F

    Cat: why are you commenting on an area you don't live and obviously know zip about? Today in Vancouver the sea temp was 11C
  5. CatrigCat
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    CatrigCat Junior Member

    Well, if seawater is cool enough that an air handler can pump out cool air, USUALLY the outside air is cool enough that popping a hatch will also cool down the interior.
    When it's hot outside, seawater is not cool enough for the air handler to work.

    IMO the best way to cool the boat when it's hot outside, is to pump seawater on deck.
    That is until the people from the marina complain that you should stop 'washing' your boat inside their marina. :)
  6. PAR
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    PAR Yacht Designer/Builder

    In the Caribbean, where the water isn't so cool they use a "swamp cooler", which is much as Gonzo described. A "J" tube was run to the bottom, which prevented picking up silt and this provided water, which was pumped up to a series of baseboard heater units. A series of small pancake fans pushed air over the fins and out a couple of vents, per length of baseboard heater. These heaters were stripped of their housings and usually placed in wooden boxes around the top of the cabin walls.


    A small pump and some fans, after you make enclosures around the cabin. It's not A/C, but does lower temperatures quite a bit and uses very little energy. The only bit of trickery, is to figure out the size of a restriction orifice, so the water can return to the sea, with enough resistance to draw off the coolness first. Most just played with various washers in the end of the return hose, drilling out the hole until it worked the best.
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    FAST FRED Senior Member

    IF the local water is cool the easy way to cool the boat is to pump cool bilge air above the cabin sole until the cool air comes out an overhead vent.

    With a sun cover you can get the interior very close to sea water temp for damn little electric consumption.

    If your bilge stinks , clean it.

  8. Squidly-Diddly
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    Squidly-Diddly Senior Member

    Good thinking, I used to live in a 1960s vintage American house w/out AC, but the Heater had a "Cool Fan" setting that seemed to pump air from some mystery spot even on the hottest days. Not strong like AC but if you kept the house closed it worked perfect.
  9. CDK
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    CDK retired engineer

    I once spent two weeks in a beach hotel in Tunisia where they had mounted central heating radiators against the ceiling and pumped seawater through the system.
    It was scorching hot in there, the whole project was a waste of money because the temperature difference was insufficient.

    Moving air with a fan also doesn't lower the air temperature but it improves evaporation and gives a subjective cooling effect.
  10. groper
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    groper Senior Member

    Indeed , you need at least 10 deg temperature difference between the ambient air and the coil for it to be able to exchange a significant amount of BTU s. You can offset that a little by using much bigger coils but it gets impractical below 10deg td. If your lucky enough to have real cold water handy, go for it. Where I live tho, the water temp is about the same as the air, maybe 3 or 4 deg difference , hence its not realistic here...
  11. W9GFO
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    W9GFO Senior Member

    I can see no advantage to restricting the water flow.

    If the objective is to warm the water, then yes, you would want to slow it down so that it has ample time to warm up. However, the objective is to transfer heat to the ocean from the cabin. In that case you want to maintain the largest temperature differential as possible, so that heat is carried away most efficiently. The faster the flow, the cooler the water will be, so the better the heat exchange. Slowing the water flow will reduce heat transfer from the cabin to to ocean but will increase heat transfer to a given volume of water. You don't want the cooling water to hang around warming up.
  12. Nate57
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    Nate57 Junior Member

    I once experimented with the swamp cooler effect by attaching bug screen across the opening of a wind scoop I had on the forward hatch of my monohull sailboat. then sprayed water (just from a spray bottle) onto it. The cooling effect inside was dramatic. Always meant to rig an automatic way to spray or dribble seawater down it (without wetting the indoors).
  13. CatrigCat
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    CatrigCat Junior Member

    Like the myth that removing a thermostat will make an engine overheat because coolant is flowing too fast to absorb heat.

    I've never seen an engine overheat when removing the thermostat.
    They all run way cooler than they should.

    But I've heard that it happens.
    It is because of badly designed cylinder heads with inadequate and/or partially clogged cooling passages.
    Removing the flow restriction i.e. thermostat, reduces the pressure in those partially clogged cooling passages making the coolant boil locally at normal temperatures creating steam pockets.
    The steam pockets further reduce coolant flow, locally overheating the cylinder head and creating even bigger steam pockets, eventually leading to a partially overheated engine with coolant flowing at temperatures well below boiling.
    It looks like coolant is flowing too fast to absorb heat but it is not. :)
  14. PAR
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    PAR Yacht Designer/Builder

    I've seen plenty of engines overheat from removing the thermostat. Automotive systems require the coolant be contained in the radiator, to cool, while the fresh replacement in the block warms up. Without the thermostat, eventually all the coolant becomes the same temperature, which will be hotter than desired. You don't think they would install a part if they didn't need it, do you? NASCAR racers don't run a thermostat, but they do run a restriction orifice in a thermostat housing, to provide time for the warmed coolant to get cooler in the radiator, before being sent back to the engine. This is simply because they have so much cooling capacity at 170 MPH, they can get away with it. Try this with your pickup truck, hauling a full load and see what happens, after several hours of continuous operation. I hear this all the time, but down here in the tropics, where cooling systems need to be in good shape, we see lots of transplanted northerners, having done this for years, needing new head gaskets and related repairs, because of this mistaken belief they're more clever, than the engineers that developed the cooling systems in their equipment.

    The thought with the restrictor orifice on the DIY coolers, was to keep the water in the exchangers slightly longer and it was common to see them. This wasn't a unit generated by anything more than fishermen and farmers, looking to get something done on the cheap. I agree it's dubious at best on this type of system, though (again) it was well regarded in the islands.

  15. CatrigCat
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    CatrigCat Junior Member

    Off Topic

    Removing the thermostat without installing a restriction orifice in the thermostat housing may cause water pump cavitation and/or the creation of steam pockets in places where the higher flow rates cause significant pressure drop.

    I don't know anything more so I cannot contribute to this thread any more. :)
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