Cooling Tank for Aircon unit

[Pelagic]

I have a reserve water tank">fresh water tank of about 90 US Gallons that I never use.
Considering turning it into a freshwater cooling system for my small Aircon in the Dinning salon.
1 Steel Tank is integral to hull so skin cooled
2 Average Sea Temp 28°C
3 Tank Volume 90 USG.

Is there a formula to calculate if that Tank capacity would be sufficiently large enough to cool running aircon for 3-4 hrs at a time?

[Rumrace]

My air conditioning likely spit out 3 gallon of water out of the boats air. I made a cold air fan years ago with a Chevy heater core and a cheap bilge pump. Works but doesn’t remove humidity. In fact the cooler air seemed to make it more humid.
I have an optional additional 130L tank and a single head. We drain the main tank after a couple days. The 130 is really helpful.

[rslifkin]

It will work for some period of time before the water gets too hot. However, because the water will be warmer than the outside seawater, you'll get less cooling (and the system will use slightly more power too).

[valhalla360]

Yes, the skin will provide some cooling but I doubt it will be very effective.

A quick test might be to measure the temp of the outflow when using direct seawater cooling. I can feel the difference to it's quite a bit warmer.

1 BTU is the heat required to raise the temp of water by 1 degree Fahrenheit.

90 gallons will be about 750lb.

28c = 82F.

A relatively small 12000btu air/con will add about 16F per hour to a full 90gal tank...So after an hour, it will be up around 98F and rising.

I know our air/con was substantially less effective when the water temp was up around 100F.

Now if you plumbed it into your hot water heater to preheat your hot water, that might be a viable use.

[Pelagic]

Originally Posted by valhalla360

Yes, the skin will provide some cooling but I doubt it will be very effective.

A quick test might be to measure the temp of the outflow when using direct seawater cooling. I can feel the difference to it's quite a bit warmer.

That's what got me thinking.
There was negligible difference in Temp between the outflow and seawater.

I think I'll just mock it up and test how much temperature climbs in tank

[RaymondR]

Simms gives heat by conduction as.

Heat=kA(Th-Tl)/d

where H=heat in btu, k is the conduction coefficient with carbon steel quoted as 333 Btu-in./h-ft^2-degree F, Th temperature on the high side, Tl temperature on the low side, f the thickness in inches.

So the conduction is the product of the temperature difference, how well the steel conducts heat, the temperature gradient, the thickness of the steel, and the area subjected to the temperature gradient.

Should be fairly easy to calculate and the extra volume will give yo a considerable buffer as the volume heats up to provide the temperature gradient.

My guess is that you have more than enough cooling. I had a yachting acquaintance who did what you propose by plating in a volume between two of the frames on his Adams 40 to do what you propose to keel cool a 10hp genset and it worked fine.