Watermaker in cold seas

[TeddieBear]

Hi,
Is anyone using an heat exchanger to warm the sea water up to maintain decent yields in cruising areas where the water is cold ?


Given a fresh water ouput divided by at least two folds with the sea temperature in the low 40s, i am considering using a water/water exchanger

coupled with the boat main heater, an Eberspaecher hydonic already producing hot water for the radiators.
I have seen several exchangers notably for pools with a price tag quite attractive vs. buying a more porwerful watermaker or just adding membrane units to increase its capacity.
However given the salty sea water input i am not sure what kind to consider ? tubes ? plates ? stainless or titanium ??
Thanks

[lamadriver]

I made a very simple one, a copper tuber in a copper tube. Basically i let the coolant that ran from the engine to the hot water tank flow through a solid tube surrounded by the intake water for the h20 maker.

See picture.
This raised teh temp 6-10C and made a bg differnce. We were operating in water temps between 2- 8c. .

you need to be careful as you dont want the water temp above 28c as you could melt / damage a membrace.

there is a formula about production decrease with water temp. the other real issue is the increase of pressure in the system. I blew an oring in a energy recovery system because the water was too cold.

you could also use a brazed plate hest exchanger (BPX from Xylem)but salt water is very cossoive and id be afraid of cross conamination.

[a64pilot]

One would assume that you could tap the water heater supply and T it off to the watermaker, using another heat exchanger that seawater flowed thru, maybe a small water heater?
It should not be hot at all, if you started water flow when the engine started, and you would have to be careful that there is enough water flow to exceed the watermakers requirement.

Obviously don’t start with a hot engine.

Having said that, I think I would try to live with the lower output myself, unless your having to run your engine to make water now, plus of course initially you would need to monitor it to ensure the water wasn’t too hot, you had enough flow etc.

Maybe find a scrap airconditioner and get it’s water cooled condenser out? Run engine coolant through the inside where refrigerant normally runs and Seawater through the outside where seawater has always run?
Lots, lots more surface area there as I think many have internal fins and it ought to solve the corrosion issue.

[TeddieBear]

Thanks for this interesting feedback.
I am also concerned by the potential corrosion of the plates of such heat exchangers, i heard some use titanium ? exchangers used for warming up domestic pools with a kind of salt system vs. chorine to keep the water clean ??
My goal is to take the water from say 40F/5 C to ca. 60 F max, not the optimum around 77F, but already a nice boost in production.



Coming back to the boat i understand using the engine or the boiler is tempting, but as a central heating system is available (see Hydronic Eberspaecher marine site) i would rather use the hot water coming from this diesel heater, just by adding a by-pass on the radiators loop. I am not keen on messing up with the engine set-up and read another thread on the forum, in case of contamination of the watermaker input water by glycol used in the engine exchanger (e.g. a tiny hole following some corrosion start) this could be lethal


PS just looked at the Xylem BPX literature
https://documentlibrary.xylemapplied...C-316A-BPX.pdf


quite interesting, but dont know about salty water ??

[lamadriver]

An eperspacher hydronice heater uses glycol not water in the heating loop to the radiators.

Im not sure i understand A64's comments. in what i described there is no T, its just heating via conduction . no way to leak , doesn't matter if you have a hot engine or not or if the engine is running. Mine was set up to work when the engine was running, creating heat. You could run it with the motor not running you just woudlknt boost the temp .

You motor all the time in the south any way , so if we were mtoring i ran the water make.

[kmacdonald]

If you do something like you suggest make sure the heat exchanger is suitable for potable water.

[a64pilot]

Originally Posted by lamadriver

An eperspacher hydronice heater uses glycol not water in the heating loop to the radiators.

Im not sure i understand A64's comments. in what i described there is no T, its just heating via conduction . no way to leak , doesn't matter if you have a hot engine or not or if the engine is running. Mine was set up to work when the engine was running, creating heat. You could run it with the motor not running you just woudlknt boost the temp .

You motor all the time in the south any way , so if we were mtoring i ran the water make.

You had one tube inside of another, of course it’s conduction but you could get a leak on the inside tube, and that would allow the antifreeze to mix with the raw water.
What I was suggesting was the same as one tube inside of another, but lots more surface area to conduct lots more heat.

Either engine or Diesel heater, it will be filled with antifreeze, and while non toxic antifreeze exists, is not often used.

I woudn’t worry much about the toxicity, millions of boats circulate antifreeze through their water heater now, without toxicity problems, but then most don’t drink water from the heater either, so who knows?

The T I was suggesting would route water from the get heater to the heat exchanger for the water maker, a lot of how much heat you need is of course predicated on the amount of raw water flow, my water maker flows 1.6 gallons of water per min., and that’s a lot of water to heat, low output water makers will of course flow less water.

[Tellie]

Yeah pre-heating the water is a tricky thing because watermakers don't like hot water and if it gets too hot you can certainly damage the watermaker components. Plus depending on the size of the watermaker as well depends, as mentioned above, the flow rate of the watermaker. A higher capacity watermaker will flow a lot of water that would be difficult to properly and evenly heat.

[Clivevon]

Hi. I know virtually nothing about watermakers or how much seawater intake they need to produce fresh water, so please excuse me if this is a stupid idea. But to avoid the risk of poisoning yourself or overheating the water feed to the watermaker, why not just have your seawater intake feed into a small tank somewhere inside the accommodation onboard & let it rest there for a while to warm up before feeding into your watermaker. You could install a small extra radiator beside it or under it to help warm up although not connected in any way to your heating water system?

[TeddieBear]

That would be a simple solution but unfortunately the raw water flow is far too important. I dont know the formula but the water output is only a (small ??) percentage of the raw water intake also used to continuously rince the membranes, etc otherwise quickly clogged with salt...
With water in the low 40s (5 Celsius) not too worried about overheating. Would be happy to just take the water to 60 F. I am amazed a single tube could do it and hence looking at actual exchangers.
I am concerned though with corrosion of the plates or pipes and by potential contamination/toxicity.

I understand the radiators loop operating with only pure water in it would be risky in cold weather, but as already mentioned above could use a non toxic anti-freeze instead of the commonly used glycol, for instance glycerol

not dangerous, only potentailly laxative well after drinking significant quantities !

Finding an exchanger with materials suited for drinkable water and resistant to salt corrosion seems a real challenge though.

[joelhemington]

Originally Posted by TeddieBear

Hi,
Is anyone using an heat exchanger to warm the sea water up to maintain decent yields in cruising areas where the water is cold ?


Given a fresh water ouput divided by at least two folds with the sea temperature in the low 40s, i am considering using a water/water exchanger

coupled with the boat main heater, an Eberspaecher hydonic already producing hot water for the radiators.
I have seen several exchangers notably for pools with a price tag quite attractive vs. buying a more porwerful watermaker or just adding membrane units to increase its capacity.
However given the salty sea water input i am not sure what kind to consider ? tubes ? plates ? stainless or titanium ??
Thanks

Maybe something like this would help https://www.watlow.com/products/heat...SAAEgJFevD_BwE

[Lepke]

Since I'm running a generator anyway I made a heat exchanger with an electric element. Since I flush after making water with fresh, I'm not getting a buildup.
Max temp for my Filmtec membranes is 113°F. I only heat to about 70°.

[PirateFoxy]

Originally Posted by TeddieBear

That would be a simple solution but unfortunately the raw water flow is far too important. I dont know the formula but the water output is only a (small ??) percentage of the raw water intake also used to continuously rince the membranes, etc otherwise quickly clogged with salt...
With water in the low 40s (5 Celsius) not too worried about overheating. Would be happy to just take the water to 60 F. I am amazed a single tube could do it and hence looking at actual exchangers.
I am concerned though with corrosion of the plates or pipes and by potential contamination/toxicity.

I understand the radiators loop operating with only pure water in it would be risky in cold weather, but as already mentioned above could use a non toxic anti-freeze instead of the commonly used glycol, for instance glycerol

not dangerous, only potentailly laxative well after drinking significant quantities !

There is anti-freeze intended for winterizing RVs that is non-toxic, although apparently the taste/smell is not terribly pleasant and can take quite a lot of flushing to get rid of. But assuming it meets spec for the heating system that’d be safe enough to use since the idea is to not have it IN the potable water in the first place anyway, it’s just in case of leaks.

[Tellie]

The problem is several fold. First the most important part, raw water intake flow to even a smaller watermaker is fairly voluminous. You would have to have a very large tank to store enough water that you could moderately and evenly heat. At just 2.5gpm for an average sized watermaker most sailors would be looking at, would mean that you would have to evenly heat at least 150 gallons an hour to make maybe 15-20 gallons per hour. Pretty tough task to accomplish on a small boat with cold incoming water to deal with as well. Second, running such a set up that could evenly heat that much water in such a time through a heat exchanger on a diesel engine? Why not just add a big radiator from an 18 wheeler to your diesel cooling system and see how long your engine lasts. You have to extract heat from your engines cooling system to accomplish this. In the conditions of already very cold water you are sailing in the engine already has to heat it's own cooling fluids to operable temps. Adding a huge radiator makes that a lot more difficult. I doubt many engine manufacturers would smile on that idea. Then what happens to this heated water when the watermaker is not being operated? Would you have a way to cut off the heat exchanger when the watermaker is not working? If you motored for a few hours and then decided to make water where is the temperature of the stored water after a three hour motoring? Pretty warm I would guess, far to warm for a membrane and critical components to many watermakers. It's a fun idea to kick around but extremely unpractical for cruisers. I actually have several customers that sail to the arctic regions, mostly research type vessels or extreme adventurers. No heaters on these watermakers. We do though however insulate the membrane vessels in extreme conditions. Here's the best solution. Heat up enough water for a cup of tea, let the watermaker run a bit longer and be happy.

[TeddieBear]

Originally Posted by joelhemington

Maybe something like this would help https://www.watlow.com/products/heat...SAAEgJFevD_BwE

electric heating is a possibility, but then it's a trade-off of additionnal power used for pre-heating the raw water vs. letting the watermaker operate longer.
I dont know how to do the maths, but that must be possible to calculate if there is an actual benefit or not.


As i believe large exchange surfaces are required to pre-heat a significant flow of low temperature sea water, and a diesel water heater is available for the radiators central heating system, i keep looking at water/water heat exchangers. By the way these fuel operated water heaters (Eberspaecher hydronic, but also Webasto, etc) can also be used for warming up the engine and for producing hot water on board.


I am making some (slow) progress and found exchangers with the appropriate capacity ratings and moreover suitable for potable water :
see for instance : https://rheem.co.nz/assets/Brochures...ure-110419.pdf


however since i have been told titanium plates would be better than stainless steel re corrosion resistance, i am still searching !