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Old 05-01-2021, 16:35   #31
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Re: Using Generator Cooling to Heat Water

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Originally Posted by Manateeman View Post
The FDA will not permit you to use ethylene glycol in any coil or plate heat exchanger. You never see it in food processing plants. Your lungs “drink” hot water when you are in the shower.
It’s very, very difficult to detect in process water but it accumulates in your tissues so even tiny levels build up over time.
I know, it is used in some boats but why take a chance with such a toxic chemical. Why do you think it’s prohibited in food processing? I don’t think anyone looks at issues like this in yachts so there is no data.
No data does not equal no cases.
You get sick and do you think anyone would connect the hot water system on your yacht with your illness? Remember Legionnaires Disease? It was a long time before anyone looked up on the roof and did a test.
Ethylene glycol is a great way to kill someone painfully. I’m not going to get into the pressure / pinhole discussion in which I don’t concur with you. Let the owner decide what risk he is willing to take. My post was intended to provide additional facts and not simply opinions. It’s a toxin. The FDA is aware of the danger in a heat exchanger application. It can accumulate in your body and you and your Doctor might not discover that the source of your illness is on your yacht.
High downside risk, not much benefit. But...
Happy trails to you.
Mark and his “please don’t pee into our drinking water sea” manatees
So I don't think you're getting the fact that not only does almost every cruising boat out there already do this with their main engine but the OP also already does this with his main engine so he's obviously aware of and already accepted this "risk" if it exists!

No data might not equal no cases, but when the vast majority of the fleet is doing it and has been for decades you would expect to at least be able to point to one case if it was indeed an issue. I'm not aware of even one case, are you?
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Old 05-01-2021, 17:51   #32
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Re: Using Generator Cooling to Heat Water

How about just wrapping a copper water line from the fresh water pump around the exhaust manifold on the gen set before it reaches the hot water heater??
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Old 05-01-2021, 18:14   #33
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Re: Using Generator Cooling to Heat Water

I was once on the hard so I plumbed my raw water cooled fridge in to my fresh water tank and it got the water toasty warm !
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Old 05-01-2021, 19:53   #34
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Re: Using Generator Cooling to Heat Water

sounds like a really good idea. our gennie is only single cylinder but gota put out some heat and so might as well use it.

we have engine hot water plumbed already so should not be too hard to connect the gennie as well

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Old 06-01-2021, 03:38   #35
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Re: Using Generator Cooling to Heat Water

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Dumb question Sailmonkey, I suppose that the thermostat is normally closed and therefore the thermostat bypass hose is the coolant hose right ahead of the heat exchanger. That is where I was going to connect my loop. Are you suggesting something different?


This is the hose I was speaking of, located between the water pump and the thermostat housing.

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It’s a smaller hose, but used to make plenty of hot water on our boat before I nixed the water heater.
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Old 15-01-2021, 10:42   #36
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Re: Using Generator Cooling to Heat Water

One alternative comes straight from water heating solutions common to off grid housing: use the waste heat from the engine exhaust (main, genset, or both) as your primary source for heating water. For all practical purposes, the energy is free (having already been paid for by the combustion process).
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Old 15-01-2021, 21:42   #37
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Re: Using Generator Cooling to Heat Water

I think you are overly concerned about the antifreeze risk.
Agreed that antifreeze is toxic, but it is important to recognize that toxic impacts on people depend on a combination of the toxicity of the substance in question and the dose. The risk of a toxic dose of antifreeze is extremely small, far below the risks we all run in day to day life, such as driving a car or falling overboard.

Thousands of boats use heat water with the engine cooling fluid (i.e. water + antifreeze)
I have never heard of a health damage in practice. Have you any documented cases?
If so, please post to educate us.
Heating water with a diesel generator is no different.
Traces of antifreeze too dilute to smell will do people no harm. Washing dishes and showering with traces of antifreeze is not a danger.
Any more than a tiny trace is obvious, particularly if used to cook food or make coffee etc.
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Old 15-01-2021, 22:06   #38
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Re: Using Generator Cooling to Heat Water

notice folk talking about risk with anti-freeze when making hw

admittedly we don't use anti-freeze here, but i think you need to realise that the hw running from the engine through the hw system is the salt water that cools the engine fw via the heat exchanger. it's not the fw (which circulates through the engine and contains the anti-freeze)

at least that is how it is in our boat.

consequently there is no risk of coming in contact with the anti-freeze

cheers,
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Old 15-01-2021, 22:42   #39
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Re: Using Generator Cooling to Heat Water

The waste heat from engine exhaust is much hotter than heat transferred from the engine coolant, and warms up instantaneously for all practical purposes. It would be a far more efficient source of heat to scavenge for heating the vessel's hot water tanks. Temperature control is a trivial exercise: circulating pump control via a thermostat. When the tank is up to temperature, it might be necessary to prevent over-temperature problems in the heat exchange circuit, but at most that would entail including a thermostatically controlled bypass. It's a simple engineering exercise.
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Old 16-01-2021, 04:45   #40
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Re: Using Generator Cooling to Heat Water

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Originally Posted by chrisr View Post
...the hw running from the engine through the hw system is the salt water that cools the engine fw via the heat exchanger.
Quote:
Originally Posted by Robert Jansen View Post
The waste heat from engine exhaust is much hotter than heat transferred from the engine coolant, and warms up instantaneously for all practical purposes. It would be a far more efficient source of heat to scavenge for heating the vessel's hot water tanks.
Interesting. I've never seen a water heater hooked up this way. I've only seen jacket water (closed loop) used. Is using raw (exhaust) water common somewhere? I'm very curious how that would work. We don't appear to be talking about raw water cooled engines here, unless I missed something.

In most wet exhaust systems, the exhaust/water/steam all exit together through an exhaust hose. That hose is too large diameter to be any use in a water heater loop.

There are also systems which separate the water downstream and allow it to drain (via gravity) below the waterline, to reduce the splash sound of the exhaust. But I'd be surprised if there's enough pressure there to run it through a water heater loop, unless the water heater were precisely placed between the level of the exhaust separator and the waterline. And such a system could introduce the danger of hydro-locking the engine.
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Old 16-01-2021, 04:56   #41
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Re: Using Generator Cooling to Heat Water

Quote:
Originally Posted by chrisr View Post
notice folk talking about risk with anti-freeze when making hw

admittedly we don't use anti-freeze here, but i think you need to realise that the hw running from the engine through the hw system is the salt water that cools the engine fw via the heat exchanger. it's not the fw (which circulates through the engine and contains the anti-freeze)

at least that is how it is in our boat.

consequently there is no risk of coming in contact with the anti-freeze

cheers,


I’d need to see proof of that. The seawater isn’t hot enough after passing through the engine to heat water beyond lukewarm. And that would take hours.
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Old 16-01-2021, 09:54   #42
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Re: Using Generator Cooling to Heat Water

I did a quick search. see:


https://polarpower.com/products/gene...eat-exchanger/


The solutions appear to be off the shelf.


This is just one of many results from searching waste heat for water heating.



Using exhaust waste heat to heat water takes advantage of the 75% of the fuel burn that goes up the exhaust as waste heat. That should be all the information you need to inform your decision.
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Old 17-01-2021, 17:29   #43
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Re: Using Generator Cooling to Heat Water

Good find, in my case I was lucky enough to have a Water Heater with two separate coils, one connected to the main engine and the other one left unused. There was no need to add a separate heat exchanger. I modified the plumbing of the Onan Generator such that the coolant gets diverted to the water heater 2nd coil before it goes into the heat exchanger. The double coil are such that the main engine and generator cooling circuits remain completely separate. As a matter of fact they each require a different type of coolant. The Onan quickly reaches 74 Celsius in operating temperature before its thermostat opens and runs at that temperature through its load range. We get hot water in about 15 to 20 minutes as opposed to between an hour or two. So far the water pump of the Onan seem to deal with the enlarged circuit just fine. The electric power freed up allows my to use deeper cycles on my batteries and use the freed up power to charge them in bulk mode for longer periods and still load my generator to about 75% of its nominal capacity which is what Onan recommends. Someone made a good comment stating that the dealer recommended to run the generator at high load using the electric water heater and if necessary the air conditioning. Dealers push us to buy big gen sets and once we own them they warn us against not loading them enough... How about selling us a correctly sized generator and offer as an option a kit to make good use of the cooling heat that would otherwise get wasted to the sea? So far we are very pleased with the setup.
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Old 17-01-2021, 17:40   #44
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Re: Using Generator Cooling to Heat Water

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Interesting. I've never seen a water heater hooked up this way. I've only seen jacket water (closed loop) used. Is using raw (exhaust) water common somewhere? I'm very curious how that would work. We don't appear to be talking about raw water cooled engines here, unless I missed something.

In most wet exhaust systems, the exhaust/water/steam all exit together through an exhaust hose. That hose is too large diameter to be any use in a water heater loop.

There are also systems which separate the water downstream and allow it to drain (via gravity) below the waterline, to reduce the splash sound of the exhaust. But I'd be surprised if there's enough pressure there to run it through a water heater loop, unless the water heater were precisely placed between the level of the exhaust separator and the waterline. And such a system could introduce the danger of hydro-locking the engine.
You are right and I would not want to run hot salt water in my water heater, I don’t think the coils would last very long. In my case I run coolant from my generator into a dedicated coil in the water heater.
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Old 17-01-2021, 17:50   #45
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Re: Using Generator Cooling to Heat Water

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I was once on the hard so I plumbed my raw water cooled fridge in to my fresh water tank and it got the water toasty warm !
That’s a really interesting idea. My wife and I just spent a week on the hard without fridges running and I was considering adding a fan driven heat exchanger so that next Time we would have a fridge working on the hard. Frigoboat offers this as an option. I like your setup much better. I suppose you use two keel coolers, one in the water tank and the other under the waterline? I suppose the first cooler in the line is the one in your water tank and the 2nd is the one on the outside of the hull just in case your tank water does not give you enough cooling?.
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