All marine aircon needs sea water ?

[hellosailor]

"The compressors on automotive AirCons are typically engine driven, and the excess heat from the cabin is circulated out though the radiator in the engine compartment"
AFAIK, never. Not quite. The AC system in a car uses an external evaporator coil, which is normally placed in front of the radiator so it gets the first shot at the cool air coming in the grill. And there's either a large fan sucking air through, or masses of air from the highway being pushed through.

Water can absorb an incredible amount of heat compared to air, so using a water-cooled system allows for much smaller heat exchangers or much smaller quieter fans, etc. I've seen different numbers but all are way more than 10x better heat absorption for water.

[Mike Banks]

There are air-cooled units like the household types. Large and bulky if they are efficient--but the ones that use part of the already cooleed air to cool the incoming air are useless except for use a dehimidifiers, and only then if you have access to a marina power supply.

Seawater cooled is the way to go. Much smaller, more efficient, and I believe quieter. Good enough to run from a diesel gen-set without breaking the bank on those sweltering humid days you can not get by with fans while cruising

I would not have an air-cooled set unless I had it demountable on a panel to fit into a hatchway--for use only at a marina with power. It would need its own weather protection. Totally useless while sailing. I have seen them mounted into the bulkheads of boats with deckhouses--so that the water condensation dribbles on to the deck or is taken by a drain over the side. I still prefer the water cooled.

[boat driver]

Reading the discussion of units- try keel cooling-
discuss with manufacture of unit if they support option- or at least not deny warranty for unit-

The involvement involved determining the amount of cooling BTU needed for the unit and then approaching the closed loot design/install. I have observed external tubing looking like a refrigerator coil ( it was a stainless tube looking very similar to a commercial freezer unit part) with the refrigerant pumped thru it- (no water) as well as a number of units with a glycerol fluid. metal hulls can have the tubes welded internally and externally to do the same thing.

simply think outside the box as a geothermal system adapted to a boat.

My assumption to why the concept is not used more often is the added up front expense and more difficult ability to after-thought install in production boats.

The plus of this type unit- keeps unit in engine room, reduces maintenance of water, removes a seacock and no strainers to clean.
negatives- often needs some significant design and effort plus a haul out (if not installing new seacock in boat) and if external may increase drag on hull.

[SeaSon]

Originally Posted by Squanderbucks

I have two A/C units working off a single thru hull but it is not just a "T" in the hose. Tried that - doesn't work as intended. When running one A/C it will draw air from the one turned off and siphon air into the lines of the one working.

What I settled with is this: One thru hull and strainer, "T" after the strainer , near the secondary unit pump and each A/C has it's own pump I put a one way bronze flapper valve in the hose to the secondary units pump. That way when it is off and the main one is running the siphon is stopped.

I never run the secondary only or I guess I would need another one way flapper valve.

Putting the T after a single pump works well for 2 units and a single through hull. Either unit 'on' energizes the pump.

[Cavalier]

Originally Posted by hellosailor

"The compressors on automotive AirCons are typically engine driven, and the excess heat from the cabin is circulated out though the radiator in the engine compartment"
AFAIK, never. Not quite. The AC system in a car uses an external evaporator coil,

I should have said "a radiator" instead of "the radiator" as, clearly, it's not connected into the engine's cooling system.
However, note that the "radiating coil" that's normally located in front of the air-intake/radiator is actually the "condenser coil" not the "evaporator coil" as you stated. The evaporator coil is the cold one that sits in the air-handler and cools the air flowing into the cabin.