Can you use the heat from fridge/freezer to warm shower water.

[Grattaway]

Sure it can be done on a boat and certainly on land is not uncommon
We use shell and tube heat exchangers for our refrigeration operation and have one site where process water is heated by the same process.
Some large fishing boats do the same thing to raise water temp that feeds into hot water systems and where you have large freezing operations it make sense.
I have also seen such a set up warming glass houses

would I do it on my boat - probably not as generally not big enough/consistent enough load to make investment worthwhile. You also need space and have now something else to maintain. Maybe if I was rebuilding or starting from scratch then the likes of an Ozefridge could be designed in -certainly nothing wrong with the concept -or the question

[Sailorichiban]

Hello all,
Perhaps the waste heat from air conditioning would be more effective.
Or how about wasted heat from a generator’s discharge?
I can recall when I needed the maximum possible amount of heated water using electricity and the coolant from the main power plant. Of course there was usually the hot water kettle too!
Good luck to all!

[SV THIRD DAY]

The BTU rating of the compressors put off about the same heat as a 100W lightbulb....so that's just not going to make you enough hot water for a decent shower...even a boat shower.....and especially a shower with a friend.

[nmccubbin]

The starting point for the calculation should be the rate of heat leaking into the fridge/freezer, because that is what the refrigeration equipment must put out
A typical well built system leaks about 200 BTU/ hour
A minimal shower is about a gallon, say 8 lbs water, so it could be heated about 50F in an hour
Seems to be enough brute heat, BUT the performance of the fridge would drop with the warm cooling water, severely reducing the real benefit.
At the least, a relatively large, custom, heat exchanger.
Before spending money on hardware, have an engineer with experience in marine fridges do a proper calculation.
It is a lot easier and simpler to heat the water with an engine heatex.

[OneBoatman]

The simple answer is yes, you can retrofit most any normally air cooled refrigerator or freezer by placing a water-cooled condenser in front of it' normally air cooled condenser is similarly used with a water-cooled heat pump. A water cooled condenser is always designed with double walled pipe to ensure separation of the refrigerant and water is maintained in the case of a leak. You then are able to generate "free hot water" when the refrigerator or freezer or both are running. On a typical recreational boat there is the problem that if you are running the refrigerator full time and you are not using hot water and
replenishing the reservoir with cold you lose efficiency to condense refrigerant as the water gets hotter so the air-cooled condenser must remain to ensure the job gets done. Real money is saved in application like diners, cruise ships, and military ships where there is typically much higher demand for the hot water being made and fresh water is fed to the condenser keeping a happy thermodynamic cycle.

[Cheechako]

Originally Posted by nmccubbin

The starting point for the calculation should be the rate of heat leaking into the fridge/freezer, because that is what the refrigeration equipment must put out
A typical well built system leaks about 200 BTU/ hour
A minimal shower is about a gallon, say 8 lbs water, so it could be heated about 50F in an hour
Seems to be enough brute heat, BUT the performance of the fridge would drop with the warm cooling water, severely reducing the real benefit.
At the least, a relatively large, custom, heat exchanger.
Before spending money on hardware, have an engineer with experience in marine fridges do a proper calculation.
It is a lot easier and simpler to heat the water with an engine heatex.

Interestingly, the under settee refridge unit on my 47 footer had both water cooling and air cooling. The air fan seldom came on. I would think that would work fine for gradually heating some shower water in an insulated tank.

[DShant]

As several people have mentioned here the heat gain for the water wouldn't be great from your fridge but I have always been surprised that more new boats don't route the generator and engine exhaust heat through the hot water tank. My 1972 sail boat had a engine heated water tank. It's not exactly hi tech, pretty simple and efficient.

[Bill_Giles]

I don’t think that it is quite that simple although a brilliant idea. If you surround the fridge coils with a water jacket then it will get warm. But that will stop the fridge working. If you pipe the warm water away then you will need to store it and then circulate new cold to get the fridge operational again. when the stored hot water is used then the water will need to be diverted to the coils again.

I think that such a system might work but would be overly complicated.

[RHCAT]

My NZ built Cat came with salt water cooled Fridge (325lt) Freezer (165lt) running 2 BD35 Danfoss compressors for the former and 1 BD50 for the latter. I have had significant issues with fouling of the sea water filter and compressor heat exchange piping so decided to draw the cooling water from the single fresh water tank (approx 700lt).

There is considerable heating of the fresh water, particularly in the heat of the Brisbane summer while Marina based dodging cyclone season, that necessitates emptying the hot (35deg C - great shower temp in our climate) water by washing the vessel down and having a longer shower than the usual splash. 🙂 The lower our tank level the faster it heats up, obviously, and I change it out to reduce compressor and pump running times.
Marina town water added to keep the tank full helps stretch the dump time - btwn 2 - 3 mths depending on many factors.

Not having to rely on salt water for cooling is great when on the hard stand living on board getting lightning strike damage repaired over 4 months. The Frig-O-Boat refrigeration continuous run pump is giving much greater service life on the fresh water too.

So yes, it is possible to use refrigeration cooling to heat shower water. Drinking water is unaffected due to the distance from tank to galley tap, unless it’s on for an extended time.

OP - PM me if you need more info. (See you’re also Brisbane based)

[foufou]

On the other hand the heat from the back of a photovoltaic panel might help. Direct sunlight is about 1.4KW/sq meter. Photovoltaics are about 20% efficient, so 80% of the sunlight might be converting to heat. If you could capture that from a couple of square meters you would get some benefit. YMMV