Is it Possible to use Fridge Condenser to Heat Water ?

[pdbms]

Rather than waste the heat from the fridge and freezer, can I create / purchase a heat exchanger to heat hot water for showers / galley?

If I do it this way, what happens when the hot water system is up to running temperature, do I then need a bypass to an air cooled condenser?

[downunder]

I believe it is?

Outback Marine at Gold Coast use such a system for their Argus 35 vessel.

Talking to their principle they have used the system in earlier vessels.

They will be able to point you in the right direction. Forget principle's name at this moment.

[sailorchic34]

Well supermarkets have been doing this for years.

Roughly figure 1200 btu/day per cubic foot of refrig. This is just ballpark but sort of average /close anyway. SO 6 CF fridge would reject about 7200 BTU per day, which in theory is available to heat Oh about 8 gallons per day in a perfect world.

The main problem I see is that as your heating the water with say 300 btu per hour the tank will be loosing heat at a hundred or two btu's per hour, due to more surface area. It works with large compressor racks but with a little BD50 theres probably not enough capacity to make it efficient.

[hellosailor]

Between the cost of the engineering, the cost of monel (presumably) heat exchangers custom built, the space lost, the need to have the shower back-to-back with the fridge and freezer (or have longer line losses), the space for the highly insulated storage tank...I suspect the answer is "If you have to ask, you can't afford it."

Possible? Absolutely! Economically feasible? I don't think so, unless you've got a whopping huge reefer to supply lots of waste heat, and you like lots of hot water.

[downunder]

Link to Outback marine system

Outback Marine Refrigeration

Their website has a lot of good information on marine electrical and refrigeration design

http://www.outbackmarine.com.au/shop...al-Systems.481

[Cheechako]

the water will get too hot and shut down the fridge overtemp I would guess. I tried this when on the hard in Trini using a 5 gal bucket cooling my AC unit (water cooled ac) the water was hot in about 5 mins and shut down the unit!

[downunder]

From outback marine website:

Using familiar Danfoss DC compressors, Veco have developed condensers sets that are efficient to run and are built to last. With the best gear and in house enclosure manufacturing capability, Outback Marine can supply a solution ranging from a DIY component kit to a fully integrated refrigeration system.
A recent development was an entirely new marine refrigeration system that would use otherwise wasted energy to heat the vessel’s hot water system. Unlike conventional water cooled marine refrigeration systems which pump condenser heat overboard, the otherwise wasted energy is recovered to heat the boat’s on-board hot water system. The system will heat water to around 40º C, which is considered sufficient for most showering requirements. A digital control panel is supplied to supervise refrigeration and hot water temperatures. This innovation by itself does not at first look like a big deal, but considering that with a solar panel array, the system eliminates the need for an on-board 240 volt generator or LPG. The benefits can be outstanding

[sailorchic34]

That sounds interesting. I could not find much info on their site about the heat pump option. I'd like to see how they get usable heat out of a cycling BD50 in a water source application. Plus it would be interesting to see the total amp draw (compressor and water pump) compared to a typical air cooled or water cooled unit.

There would also be problems using engine jacket heat to heat the hot water as then the water temperature could be too hot for the compressor.

[Richard Kollmann]

There are ways to recover heat but it would require an extremely large refrigeration unit to make this worth while or make this small amount of heat usable. A simple heat comparison would be taking heat from a pleasure boat’s refrigerator using a BD 50 compressor operating an evaporator temperature at +12 degrees F. This BD50 condensing unit would produce around 150 watts of heat energy or 511 btu of heat energy per hour. When engineers calculate office space heat recovery for A/C designs they use 300 Btu added heat load for each person working in that room. A like comparison to condensing unit heat might be to recover the heat generated from two people moving around in a boat’s cabin and try to heat water with it.