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Old 17-01-2021, 18:51   #46
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Re: Using Generator Cooling to Heat Water

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Originally Posted by bclaude View Post
Good find, in my case I was lucky enough to have a Water Heater with two separate coils...
Now that's handy! You're right that it would allow you to run a smaller genset. Be it shoreside or on boats, generator salesmen always want you to buy a generator that has the capacity to run everything in your home/boat all at once. I never fell for that.

Do you do anything to prevent heat loss from the water heater back to the genset and main when they're not in use? I found this to be a real issue when on the hook. The engine coolant would circulate via convection and cool down the water heater. I plumbed in a 12VDC solenoid valve so the loop was closed unless the main was running. Presumably you could use a similar AC valve on the genset side.
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Old 17-01-2021, 19:06   #47
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Re: Using Generator Cooling to Heat Water

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Now that's handy! You're right that it would allow you to run a smaller genset. Be it shoreside or on boats, generator salesmen always want you to buy a generator that has the capacity to run everything in your home/boat all at once. I never fell for that.

Do you do anything to prevent heat loss from the water heater back to the genset and main when they're not in use? I found this to be a real issue when on the hook. The engine coolant would circulate via convection and cool down the water heater. I plumbed in a 12VDC solenoid valve so the loop was closed unless the main was running. Presumably you could use a similar AC valve on the genset side.
You are making a good point. There is a circulation pump installed on the main engine loop so I suppose this reduces the heat transfer back from the water heater to the engine block. As for my new loop connected to the generator I haven’t done anything to prevent heat escaping from the water heater back into the generator when the latter is not running. I now get hot water in 15 to 20 minutes as opposed to 1 to 2 hours before and therefore I am not hugely concerned about heat loss. Keep it simple is often the right thing to do on a boat. In our case we are headed for Patagonia and therefore anything that will slowly dissipate heat inside the boat as opposed to the ocean will be a good thing.
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Old 17-01-2021, 23:54   #48
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Re: Using Generator Cooling to Heat Water

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Originally Posted by Valmika View Post
Why not run both electrical and coolant heating elements? Seems like you would get hot water even faster then once its hot shut down the electric element and have the genset charging everything else.


Easy solution since you are not interfering with the electrical part of the installation at all.

Don't plumb it into the thermostat bypass as this will interfere with the operation of the thermostat in warming the engine up.

There is no more risk of contaminating the water supply than you already have with the main engine plumbed into the calorifier other than that of a second source of contaminants.
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Old 18-01-2021, 02:43   #49
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Re: Using Generator Cooling to Heat Water

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Easy solution since you are not interfering with the electrical part of the installation at all.

Don't plumb it into the thermostat bypass as this will interfere with the operation of the thermostat in warming the engine up.

There is no more risk of contaminating the water supply than you already have with the main engine plumbed into the calorifier other than that of a second source of contaminants.

If your fortunate enough to have a water heater that operates on the water bath principle there is no risk at all.
The principle is that the engine heats the water in an unpressurised tank via a coil in the tank, the hot water is produced via another coil within the tank, a pressure relief valve releases any hot water back into the tank with any excess overflowing to the bilge. A simple system that produces a very good quantity of hot water.
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Old 18-01-2021, 04:34   #50
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Re: Using Generator Cooling to Heat Water

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If your fortunate enough to have a water heater that operates on the water bath principle there is no risk at all.
The principle is that the engine heats the water in an unpressurised tank via a coil in the tank, the hot water is produced via another coil within the tank, a pressure relief valve releases any hot water back into the tank with any excess overflowing to the bilge. A simple system that produces a very good quantity of hot water.
In addition, of the fresh water system is pressurized to say 20 psi a leak in the heater coil from the engine is more likely to cause fresh water to contaminate the engine cooling then overflow through the expansion tank cap rather than the cooling fluid contaminate the fresh water system.
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Old 18-01-2021, 09:08   #51
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Re: Using Generator Cooling to Heat Water

Wow! An awful lot of issues being raised from the armchairs here.

It is a good idea, and it works a treat. We have a 3.6kW WhisperGen DC generator with a coolant loop through the water heater. It heats the water fast, and free. For us as a long range cruising boat this make a lot more sense than using a coolant loop from the drive engine. We have hardly any need for domestic hot water while on passage, and we use the drive engine rarely while underway, and never while at anchor.

While a leak from the stainless steel heat exchanger pipes inside the hot water heater is theoretically possible, it is highly unlikely, and a "poisoning" is even more unlikely. Ethylene glycol has a very distinct smell and taste, and in addition commercial coolants have a dye added that is quite obvious even at very low concentrations. Do not run your engine without the correct type and concentration of "antifreeeze." It is needed for corrosion protection even in the tropics.

You will not cause the engine to run cooler than it otherwise would. There is simply not enough heat capacity in the hot water system to soak up a significant proportion of the engine waste heat.

Someone suggested using the raw water as the heat source. This is not possible. Raw water exiting the engine before the exhaust elbow is lukewarm at best. If it was anywhere near as hot as your domestic hot water something would be very wrong. In addition, this would set up a whole bunch of serious and difficult corrosion issues.

A coolant loop like this will quickly heat the hot water tank to the temperature of the engine coolant. Typically 180F, or there about. This is WAY too hot for safe use from a tap. Every hot water heater SHOULD have a tempering valve on the outlet that bleeds cold water in to control the maximum temperature of the supplied water. Not just for safety, but it lets you routinely heat the tank much hotter than needed for tap water usage and thereby be able to supply a lot more hot water from the same size tank.
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Old 18-01-2021, 14:23   #52
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Re: Using Generator Cooling to Heat Water

I have the same generator as the OP, have it plumbed to my hot water heater for several years now. Wonderful setup, only complaint is the water sometimes gets too hot, and I have to barely crack the hot water on in the shower with the cold water 100 open.
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Old 18-01-2021, 14:41   #53
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Re: Using Generator Cooling to Heat Water

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Originally Posted by bclaude View Post
..I haven’t done anything to prevent heat escaping from the water heater back into the generator when the latter is not running. I now get hot water in 15 to 20 minutes as opposed to 1 to 2 hours before and therefore I am not hugely concerned about heat loss...
Fair enough, if you're running the genset regularly anyway. I try to put it off for as long as I can, especially in a quiet anchorage with other boats around. So for me, being able to avoid heat loss from the water heater is a good thing.

One thing I didn't do, but probably should, is add two valves to isolate the entire water heater loop from the engine. That's one less thing to worry about when draining the engine coolant for whatever reason; just close the valves. And if you do that, you can always manually close one to prevent heat loss on those (rare, for you) occasions when you might care.
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Old 18-01-2021, 18:31   #54
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Re: Using Generator Cooling to Heat Water

Exactly the setup I have on Botany Bay and it works extremely well.

Hot water heater had to be replaced so installed new one with dual coils.
Went for the 1200W heating element for use on the 230v circuit
Generator is a Westerbeke 6kva@50hz/8kva@60hz
200A at 24V charger installed which can easily load generator to 80% all by itself (Victron 8KVA inverter charger actually, input limited to 80% if generator max)
plumbed hot water heater to generator and hot water heater is below the generator (makes purging air in lines easy), both input and output at hot water heater have ball valves so 4 ball valves, two for main engine, two for generator.

What I find is when batteries are being bulk charged the water gets quite warm within about 30min, once load on generator drops below 60% a solid state relay brings the hot water heating element online which brings load back up to 80% and tapers from there as the batteries charge. (Nominal charging current is about 160A until batteries get to 90% SOC and transitions to acceptance).

Very important to have a hot water heater with a "tempering valve" installed which limits the output temperature to something reasonable. The advantage of running the hot water heater at engine temperature with a tempering valve is that it makes the 12Gal hot water heater appear to be significantly larger than it is and as the temperature moves around the hot water at the tap stays the same.

I have been extremely happy with this configuration.

The only "issue" I have had is that both the generator and the main engine stay slightly "warm to the touch" due to hot water thermal siphoning up from the hot water heater into the engine blocks. This is great in that it keeps the engine warm and dry but it does result in a small amount of heat loss due to the heat being transferred back to the engines when the engines are off. Not sure if the amount of loss is enough to consider an automatic valve in each line. I find that I just close the ball valve to the main engine when I am not moving very often, I close both sets of valves when I am in the slip during the summer, during the winter I often keep them open just to keep the engine room slightly warm.
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Old 18-01-2021, 20:02   #55
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Re: Using Generator Cooling to Heat Water

On my previous boat I had a "forward biased" check valve in the thermostat bypass pipe. It was not in there to "check" anything but rather to provide a very low pressure, pressure relief valve so that when the thermostat was fully closed the impeller pump would not be highly loaded. The impeller pumps unload themselves anyway but I wanted to maintain full flow through the water cooled exhaust manifold at all times.

If you wanted to prevent thermo-syphoning through the calorifier water circuit this might be a simple solution.
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Old 22-01-2021, 15:09   #56
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Re: Using Generator Cooling to Heat Water

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Originally Posted by Emmalina View Post
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 !
I thought of this once but was adviced against doing so as the warm spot in your freshwater tanks creates a place for bacteria to grow...
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