Catigale wrote:Ive always dreamed of a simple A/C mod where a small motor picks up fresh/sea water at 50-60F, pushes it through a car type heater core, and a fan blows cool air into the boat. I think you could put this together for <$100 and run it on either DC or shore power.
This has been proposed several times before. I don't believe it will work. Small, single pass car type heater or A/C cores are designed to run at temperature differentials of 100 degrees or more. The temperature difference between the 50-60 degree water and 90 degree air may seem like a lot, but in terms of heat transfer, it isn't. In terms of cooling, you're unlikely to get out of it anything more than fan forced hot air, you'd be surprised at how much power it takes to force air through a heater core, and the pumping power to circulate the water will be totally wasted. In order to provide any kind of cooling from a temperature differential this small, you'll need a super efficient multiple pass water to air heat exchanger. These things don't come cheap and the power required to run the fan will be significantly higher than that to run a standard A/C fan; these typically run around 10A @12VDC on high. That's a battery killer.
If you search in the archives you'll find several such previous discussions, wherein those who didn't like my answer stated they were going to try it anyway. To my knowledge we've yet to hear back from any of them.
If you have shore power or already have a generator, buy a small A/C for <$100 and be done with it, just as these guys are proposing.
If you're limited to 12V only, I believe any kind of heat exchanger is out of the question, power wise. The key is to just keep the air moving. We've had good pretty good success with a combination of a windscoop in the forward hatch and a small 12V propeller type fan blowing air only. We sleep in the V-berth for exactly this reason; if you have to relegate folks to the aft, under cockpit berth, probably the windscoop won't help much unless you add auxiliary vents.
The fan I picked up for <$15 at WalMart and it draws less than 1A.
The windscoop worked fine in June in Bimini, at anchor when the boat was always bow to wind and there was always wind. It would not work so well at a dock when the wind comes from a random direction. With some attention to attachment options you can swivel it to face nearly any direction, but that can become a PITA if the wind is constantly shifting direction.
