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Old 28-05-2008, 16:44   #1
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Hot water heating off 2 engines in a cat

Has anybody built a hot water storage system that uses 1 storage tank but runs off either engine in a cat (2 x 30HP diesels)?

Not sure if it is possible or if the standard engine water pumps would dislike the longer travel distances particularly if storage tank was in one hull. Would I also need to put manual valves in to select which engine was connected to the tank so water wouldnt be running through both engines even when only 1 engine running?

Dont want to always have to run the same engine to heat water and not keen to put gas water heater in because a) expensive b) uses up my gas supplies.

TwT
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Old 28-05-2008, 22:23   #2
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The only way I can think of doing this is with two Y-valves or an A or B or Off type of manifold setup. Mixing the coolant between the two engines does not seem like a good idea because of the potential of cross contamination if something happens to one of the engines. It also does not seem like a good idea in case one of the engines loses its coolant, which would also mean losing the coolant for the other engine.

I don't think adding some hose is going to make much of a difference concerning additional resistance for the coolant pumps. At least it didn't for my coolant based onboard water heater and air heater.

I would just go with two Y-valves or the manifold setup. How hard could it be to switch them over?
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Old 29-05-2008, 08:40   #3
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Quote:
Originally Posted by Toys_with_time View Post
Has anybody built a hot water storage system that uses 1 storage tank but runs off either engine in a cat (2 x 30HP diesels)?

Not sure if it is possible or if the standard engine water pumps would dislike the longer travel distances particularly if storage tank was in one hull. Would I also need to put manual valves in to select which engine was connected to the tank so water wouldnt be running through both engines even when only 1 engine running?

Dont want to always have to run the same engine to heat water and not keen to put gas water heater in because a) expensive b) uses up my gas supplies.

TwT
I would ask some of the manufacturers if they have, or could build, a tank with twin heat exchangers. May even do this myself, haven't decided yet.

Mike
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Old 30-05-2008, 00:27   #4
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I would ask some of the manufacturers if they have, or could build, a tank with twin heat exchangers. May even do this myself, haven't decided yet.

Mike

Good thinking 99. Would reduce the cross contamination risk and make life much simpler. Assume yr building a cat then?

TwT
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Old 30-05-2008, 01:49   #5
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Yes a 12 meter Schionning Wilderness 2x 20Hp Lombardini saildrives. I am going to set one motor up with bigger alternator and pressure pump for a desalinator so this will be the main motor so hot water will probably be off only this one.

Mike
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Old 03-06-2008, 09:29   #6
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I would ask some of the manufacturers if they have, or could build, a tank with twin heat exchangers. May even do this myself, haven't decided yet.

Mike
Isotherm does - from their catalog: "Basic 40 and 75 are also available in versions with double engine water heat exchanger coils for connection also
to a water based heater system."

I've been thinking of getting one, and connecting it to the freshwater cooling systems in both my main engine and the genset. I figure if we're running the genset to charge the batteries while on the hook, it's more efficient to use the genset's heat exchanger to heat freshwater, rather than electricity or the main engine. And we get heat from the engine while motoring.

Another option if you have a wind generator is to replace the AC heating electrodes in your water heater with 12V or 24V DC electrodes. Make the wind generator shunt excess power thru your water heater...
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Old 03-06-2008, 11:09   #7
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Another option if you have a wind generator is to replace the AC heating electrodes in your water heater with 12V or 24V DC electrodes. Make the wind generator shunt excess power thru your water heater...
I'm not sure electric hot water heating is all that efficent use of your DC power. It comes at more of a premium but engine coolant needs to be cooled and heats water quite fast. You can keep water hot enough for basic purposes in the hot water tank. Since you have to run an engine some time it seems good to capture that heat.

Electric heat elements work best with shore power<g>. The traditional heat exchanger with shore power electric isn't a bad idea and covers a lot of common situations. We went another route and have hot water on demand using propane. If you think about when you really need hot water it helps decide the best route to go. How much do you need and when do you really need it?

Running collant lines a long way adds some complexity you may not want either. It could be more effective to just have two tanks with their own exchangers. One engine heats a tankful of water in a short period of time. Using two to heat it faster seems to me to be of less value. Our past boat heated 7 gallons of hot water in less than 20 minutes of engine time on a 35 hp engine. Would doing it faster be of much more value to you?
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Old 03-06-2008, 21:00   #8
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Running coolant lines a long way adds some complexity you may not want either. It could be more effective to just have two tanks with their own exchangers. One engine heats a tankful of water in a short period of time. Using two to heat it faster seems to me to be of less value. Our past boat heated 7 gallons of hot water in less than 20 minutes of engine time on a 35 hp engine. Would doing it faster be of much more value to you?
Just that in a cat you often only run one motor so was thinking less of quick heating and more of being able to heat the tank regardless of which motor was running without having to switch over.

There was also a good article in a local cruising mag about a solar powered water heater that could sit on a cabin top and be linked in with a holding tank - somebody in Oz builds a little switching / sensing smarts unit to drive the system. This assumes you have enough sunshine available to heat it and beautiful pollution free skies for the suns rays to reach the unit

TwT
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Old 04-06-2008, 11:01   #9
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I'm not sure electric hot water heating is all that efficent use of your DC power. It comes at more of a premium but engine coolant needs to be cooled and heats water quite fast. You can keep water hot enough for basic purposes in the hot water tank. Since you have to run an engine some time it seems good to capture that heat.
Well, I didn't mean it was something I would do - I threw it out as an option for those with wind generators with no latent mechanism for shutting it down remotely. Just laying out an option for others.

But I think the dual heat exchanger option is nice for those who have gensets and are at anchor the majority of the time. And you keep the cooling systems for the genset and the main engine independent.

Has anyone done such an install?
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Old 04-06-2008, 11:26   #10
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But I think the dual heat exchanger option is nice for those who have gensets and are at anchor the majority of the time. And you keep the cooling systems for the genset and the main engine independent.
I think you could assume the genset would get run regularly and might actually make enough hot water on it's own. To make it dual with one engine allows a second option. I'm not sure how many options you need for hot water.

The idea of a solar hot water heater could be quite effective. It's common to see them in the islands with shore buildings as the technology is low tech and the ability to make hot water is easy. For a cat you should have more space available. I'm just not sure how much area it would take. Mounting is a little trickier than a solar panel since you need to pipe water through it. Increased weight would require a stronger structure.

If you already have solar and wind power then you might be able to make the fridge run almost self contained but having enough to heat water seems unlikely. Being able to top off the batteries would be the starved resource at that point.
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