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Old 12-29-2015, 06:55 PM   #1
City: va
Country: usa
Vessel Name: Saltwater's Dream
Vessel Model: 1985 GulfStar 44
Join Date: Jul 2014
Posts: 8
Question Reverse Cycle AC cooling tank

To use my reverse cycle AC units in the winter, I installed a tank so I take suction from it and discharge back to it and not from/to the cold river. For heating, I take heat from the water in tank and discharge back to the tank. (experimenting). I am now experiencing where the temperature of the tank is roughly 50 degrees and seems to have extracted as much heat from it as possible. The units freeze up and blow cold air. Looking for ways to add heat into the tank to raise the temp to 75-80 degrees. Tank is 3/8 thick plastic and am leary about using immersion heaters.

Is this a good idea or any other input to make this work? Only want to use this setup in winter and shift back to the river in May. The air conditioning heated it up as for that cycle, heat is added to the tank. Already experienced this.

Has anybody ever tried this?

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Old 12-29-2015, 07:05 PM   #2
City: East Coast
Country: USA
Join Date: Dec 2013
Posts: 1,668
If you use electric resistance heat to heat the water in the tank and then use a heat exchanger to extract it, you will use more energy than if you just used electric resistance heat in the first place.

There is no "free lunch". Smarter people than you and I have tried to increase efficiency of heating systems.

After two reverse cycle AC failures (my boat is in warmer water than yours but the raw water can still hit 40 degrees, I installed an AC with built in electric resistance heating, not reverse cycle. There's no raw water input in heat mode and no reversing valves, etc.

It's not as efficient as reverse cycle but I pay a fixed rate for electricity and replacing the AC units was getting expensive.

If you really want to try heating water in an external tank to run a heat pump, think about solar.

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Old 12-29-2015, 07:30 PM   #3
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City: Essex, Ct
Country: USA
Vessel Name: Bella
Vessel Model: Mainship Pilot 34
Join Date: Aug 2012
Posts: 1,996
Wesk is absolutely right. You can't repeal the laws of thermodynamics.

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Old 12-29-2015, 09:19 PM   #4
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City: On the Great Loop - cruising down the Tombigbee
Country: USA
Vessel Name: Seven Tenths
Vessel Model: Mirage / Great Harbour 47
Join Date: Dec 2012
Posts: 237
I know of one boater who tried with some success using the "warmer" water from the bottom of the Baltimore harbor but dropping 100' of 2" plastic tubing under his boat. He connected the tubing to the input/output of his AC unit and was able to heat his boat. He had to keep the thermal loop run all the time so it did not freeze up near the surface. I opted for a hydronic heater instead.
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