Plumbing Both Engine and Genset Into Water Heater Heat Exchanger

[flippercarson]

Hello All,

We have a water heater on our sailboat with both an electric heating element and a heat exchanger which is connected to our main propulsion engine. We are full time cruisers and often spend considerable time at anchor.

I have always found it both wasteful and annoying that after a couple of days, we have to run our genset at anchor, to make electricity, to heat water, while we simultaneously eject hot water from the genset engine over the side as water heater has only a single heat exchanger coil.

I understand Isotemp makes a dual coil water heater, but apart from this, has anyone found a good way to plumb two engines (main and genset) into the same water heater, heat exchanger loop? I've considered installing a couple of three way valves to accomplish this, whereby I might "flip" the valves once at anchor so the genset would be plumbed through the heat exchanger instead of the main engine, but thought I would see if others have a solution to this challenge as I can't be the first person to try and solve this one.

Many thanks in advance for any useful ideas or suggestions.

Unhelpful comments and nasty people please just move on...

[Lepke]

I can use mains or one generator to heat my hydronic system. (I use a diesel stove with coils for heating the water heater tank.) The engines are separated by valves unless being run together. With the valves closed, each engine has it's own cooling system.
There's no reason you can't share the heat exchanger coil if your plumbing is right.

[Dockhead]

Plate type heat exchangers and separate circulation loop. Same system could get engine and genset waste heat into a hydronic heating system.

I considered this but ultimately decided it would never pay for itself versus a few dozen hours a year of extra hydronic furnace use, and I hate adding even more complexity to an already complex boat. YMMV.

What I am doing, however, is adding a bus heater for the salon into the engine coolant loop. That's minimal complexity and megawatt hours of luxurious heat whilst motoring in cold weather.

[BillKny]

When we replaced our generator we changed the plumbing so the genset cooling circuit heated the domestic hot water, and we disconnected the drive engine from the water heater.

The rational was that our need for hot water on passage was minimal, and the genset was run every other day or so at anchor making all the hot water we need for “free”.

Having both plumbed up seems overly complex for very little benefit.

[Searles]

A couple of solenoids controlled v/v energised by the gen set oil pressure sender via relays will heat the water every time you use the gen set , automatic system .⛵️⚓️

[Dockhead]

Originally Posted by Searles

A couple of solenoids controlled v/v energised by the gen set oil pressure sender via relays will heat the water every time you use the gen set , automatic system .⛵️⚓️

Wow, solenoids, relays, and electric valves! What a great idea! But couldn't we somehow make it even more complex? I bet we can think of something.

Originally Posted by BillKny

When we replaced our generator we changed the plumbing so the genset cooling circuit heated the domestic hot water, and we disconnected the drive engine from the water heater.

The rational was that our need for hot water on passage was minimal, and the genset was run every other day or so at anchor making all the hot water we need for “free”.

Having both plumbed up seems overly complex for very little benefit.

That was the conclusion we came to. Just that leaving it on the main engine was better for our use case because we like to arrive in harbour or at the anchorage with a tank of hot water for showers at the end of a long sail, and motoring in produces that .


However, for very little extra complexity other than sourcing the appropriate fittings for the genset motor, you could plumb it to be able to manually switch over. Presuming you are using the same coolant in main and genset and don't mind mixing them.

[CaptTom]

I use a solenoid valve to isolate the main from the water heater loop when the engine is not running. This prevents my water heater from heating the engine.

It's proven very reliable. Assuming compatible antifreeze, I'd consider using the same method to select between main and genset. I don't consider it overly complex, but I'd back it up with four manual valves to allow complete isolation if anything failed.

That said, my genset is oversized for my needs, and I like being able to load it up by heating water. It's not good to run them lightly loaded.

[Dockhead]

Originally Posted by CaptTom

I use a solenoid valve to isolate the main from the water heater loop when the engine is not running. This prevents my water heater from heating the engine.

It's proven very reliable. Assuming compatible antifreeze, I'd consider using the same method to select between main and genset. I don't consider it overly complex, but I'd back it up with four manual valves to allow complete isolation if anything failed.

That said, my genset is oversized for my needs, and I like being able to load it up by heating water. It's not good to run them lightly loaded.

How could the hot water heater heat the engine? The loop won't be active without the thermostat open.


Which is too bad, because I think it would be very beneficial to let the hot water heater heat the engine. Really good for the engine's health to have accelerated warm up, and the engine would just give that heat right back in a few minutes when it warms up. The problem is the thermostat however.

[rwidman]

I suggest buying that dual coil water heater you mentioned. That would be the simplest, automatic way of accomplishing your goal.

[sailingchiro]

I will leave it with one of my main engine but use the Gen-Set to electrically heat up the water if needed.

Electrically the water heats up in less than 30 minutes. Same for the heat exchanger of the main engine. Personally, I don't see the difference of running the Gen-Set to heat electrically or main engine to heat through water. Seems like we already have what we seek, redundancy.

Our main reason for the gen set is a/c, charge batteries, refrigeration, and heat water. And my wife's hair dryer.

[stormalong]

Originally Posted by Dockhead

How could the hot water heater heat the engine? The loop won't be active without the thermostat open.


Which is too bad, because I think it would be very beneficial to let the hot water heater heat the engine. Really good for the engine's health to have accelerated warm up, and the engine would just give that heat right back in a few minutes when it warms up. The problem is the thermostat however.

If your engine is very close to the water heater hot water will keep the engine warm. I do this in the winter. The hoses between the engine and the heat exchanger are about 18 inches long, simple conduction transfers enough heat that the engine block is warm to the touch.

[Flatswing]

Even if you are only running the generator to get hot water, you should run the electric element simultaneously since best to load the generator maximally & you might cut the run time by 1/3-1/2. However if you run the genny for any other reason such as making water etc. kind of a "long run for a short slide".

[Sailor647]

We found a simple solution to having hot shower water while cruising.

Our boat is equipped with a 9 gallon electric water heater that is plumbed into the diesel engine heat exchanger. We also have an Espar hydronic cabin heating system that heats water inline while the hydronic heater is running. (pic attached) The hydronic heater is not not directly plumbed to the water heater tank. So, if we are plugged in, moving the boat under engine power, or using the cabin heater in cold climates we have hot water.

While at anchor in tropical/warm climates, we have hot (then warm) water for about three days. After that, we put a solar shower on the cabin top and run the hose through the portlight in the shower. It's highly efficient at heating water even on cloudy days and can both get a hot shower daily. Sometimes the water gets too hot, so we cover it with a shade. Google solar shower.

[flippercarson]

Thank you all for the replies.

I'll sum up my responses to a whole lot of your suggestions here in a few points and I'm also posting a quick (and ugly) valving diagram.

1. Our Isotemp 55l water heater has a 750w element. To heat 55l of water from 75f to 180f takes approximately 5 hours and consumes just under 4kw of energy. That's a lot of genset run time and about a gallon of incremental diesel burn. For me, that's significant. Your needs and use may be different, but this is ours. If I can save a gallon every couple of days and significantly shorten my genset runtime and keep things quiet(er) I'd like to do it. I just hate running the genset. With the heat exchanger, in the hour or so it takes to charge the batteries, we can have our hot water and for no additional run time or cost.

https://bloglocation.com/art/water-h...e-energy-power

2. We have ample ways to ensure our Genset is already properly loaded. Adding runtime and fuel burn just for the sake of loading our genset isn't necessary for us.

3. I'd love to just purchase the dual coil version, but it won't fit in our engine room without modification as it's only available in the 40l and 75l sizes. Ours is a 55l. I might ultimately have to bite the bullet and go this route.

4. Here is a quick and ugly diagram of how I think the plumbing would need to go in order to keep the loops separate and functional. Any thoughts on simplification or something I've missed is welcome.

Thanks again.

[foufou]

Wouldn't a check valve in the place of the three way valve acomplish the same thing but automatically?