Using Waste Heat

[Dockhead]

My main engine and generator (Kohler 6.5) produce vast amounts of waste heat. I think the genset alone is supposed to produce something like 20kW of waste heat at full output.

Sailing in a cold climate, I'm constantly in need of heat, both space heating and domestic water heating. Although I have a 10kW Eberspaecher (Espar) central heating furnace on board, it seems a shame to waste all that heat coming out of the generator and main engine cooling systems.

I do of course have a loop in the calorifier which heats domestic hot water with the main engine's waste heat. This is a great thing since the crew often want showers just after getting into port or getting the anchor down, etc.

Nevertheless, I find myself very often making hot water from electricity, from the 1.5kW immersion heater while running the generator.

And the only way for me to make space heating is to run the Eberspaecher, burning diesel fuel and putting hours on that relatively finicky device, while I may be dumping 10's of kilowatts of heat overboard from the main engine cooling system -- at the very same time

I don't want to overcomplicate these systems, which require enough fiddling as it is. In years past I have rationalized the making of hot water with generated electricity by saying to myself that the little bit of incremental burned diesel fuel is much cheaper than the cost of hacking up the piping system, adding heat exchangers, or whatever else I would have to do for a theoretically more elegant solution.

So it's a tough balancing act.

What do you guys think? Some possible solutions I have thought about:

1. Install a truck heater fan coil under the companionway steps and run the engine fresh water loop through it. This would let me do space heating with engine waste heat without a lot of complication. Crude, but relatively simple.

2. Install two plate-type heat exchangers in the engine room, and run both generator and main engine cooling loops through it. Transfer heat from these to the main central heating loop for both space heating and domestic hot water. Elegant, but fairly complicated.

3. Buy a calorifier with three, rather than two loops in it, and run generator coolant through it besides just from the main engine. Let the calorifier (need to manage the flows) act as a heat exchanger, picking up heat from main engine and generator by the central heating loop. Need to modify control system of central heating system so that the pumps and fan coils will run independently of the furnace, or maybe just rely on the presence of heat from main engine and genset to make the furnace switch down to a lower output level.


Any of you cold-water sailors struggle with these issues? As I said, I'm juggling the imperatives of simplicity and serviceability against efficient use of heat, and I'm not coming up with any clear answers.

[Jd1]

The way my heating system works is the engine coolant goes through a heat exchanger (I don'y have a generator but it's coolant could go through a second heat exchanger). The heat exchanger feeds a hot water loop that has an Espar diesel heater in it. That same loop feeds the hot water tank and a string of small water to air heat exchangers that are all over the boat (about 6 or so).
I have a choice of running the Espar to heat the water going to the heaters and the hot water tank or I can use the engine heat to do that. I just finished a mod that runs the circulation pump automatically when the engine is on (previously this had to be done manually and was always forgotten).
The system works very well with hot water being generated automatically and the boat being heated if I so decide. If I stay somewhere overnight without running the engine, I can activate the Espar to both heat the domestic hot water as well as heat the boat. The boat heaters are operated by a thermostat.
The install of this system is NOT simple with hoses and wires going all over the boat ... but it works a treat.

[Dockhead]

Originally Posted by Jd1

The way my heating system works is the engine coolant goes through a heat exchanger (I don'y have a generator but it's coolant could go through a second heat exchanger). The heat exchanger feeds a hot water loop that has an Espar diesel heater in it. That same loop feeds the hot water tank and a string of small water to air heat exchangers that are all over the boat (about 6 or so).
I have a choice of running the Espar to heat the water going to the heaters and the hot water tank or I can use the engine heat to do that. I just finished a mod that runs the circulation pump automatically when the engine is on (previously this had to be done manually and was always forgotten).
The system works very well with hot water being generated automatically and the boat being heated if I so decide. If I stay somewhere overnight without running the engine, I can activate the Espar to both heat the domestic hot water as well as heat the boat. The boat heaters are operated by a thermostat.
The install of this system is NOT simple with hoses and wires going all over the boat ... but it works a treat.

Very cool -- that's one of the approaches I had in mind, but had never heard of anyone actually doing it.

I'm about half way there already since my existing Espar system does run fan coils as well as domestic hot water. I will probably be changing out the fan coils this winter, with something with thermostatic controls and quieter fans.

So does the coolant circulate through the Espar furnace without resistance, when the Espar is turned off? Or do you have to bypass it?

Do you have an additional circulating pump in the system, or do you use the standard Espar one?

Do you have a diagram of your system?

Thanks and cheers. I see you sail in a similar climate to mine.

[Jim Cate]

Dockhead, I can't make any comparisons, but we have used your "system one" for years on Insatiable II. In our case, we have no hot water tank, but do run the main engine primary coolant loop through an automotive heater. We don't have a gen set nor do we motor all that much, but when we do it provides "free" cabin heat. Have had no problems other than the usual complications when changing coolant... air locks until fully bled, just the same as if there were a hot water system instead of a heater.

We rely upon a diesel pot burner for our serious heating.

Cheers,

Jim

[s/v Jedi]

Your option #2 is the way. You should be able to use the Eberspacher circulation pump when the engine or genset is the heat source. I have seen several boats who have this and rave about it, incl. those who consider the polar regions their hang-out

[Dockhead]

Thanks for all the useful comments. I'm especially pleased to have something from Nick besides a snide comment about sailing in cold climates

How about something like this:



I would use the main engine freshwater coolant loop for all heat exchange operations.

The big advantage of this is that it would be much simpler to install, and would not require me to maintain a Micky Mouse separate cooling loop going into the calorifier.

The downside would be that waste heat from the generator would only get into the central heating system indirectly.

Another downside is that all of the heat handled by this system would go through the main engine, which would absorb a lot of it if it is cold (it weighs a lot).

On the other hand, that would be at the same time an advantage in that the main engine would be kept warm for easier starting and less wear on startup.


The other way would be to cut the existing loop from the main engine through the calorifier, make a separate short loop through the calorifier (with its own header tank I guess), which would then need three heat exchangers instead of two.

Either that, or cut the generator loop only through the main central heating loop, with no direct heating of the calorifier. I probably reject that since in summer I may want hot water heating without central heat.

[IdoraKeeper]

I have found that capturing heat from the engine when running works well, usually makes more heat than I need... Once shut down the residual dissipates too rapidly to be of much use.
If you can find a way to plumb in the genset coolant and then let the thermostat on the Espar run the furnace you will get some of what you want. There will still be waste heat in the engine space.

[djmarchand]

To give you an additional piece of data which might inform your decision: a diesel converts the heat energy in its fuel to three principle forms of energy in approximately equal amounts: work produced by the crankshaft, thermal energy in the exhaust, and thermal energy in the coolant system. So if your genset is producing 3KW (which I'll bet is closer to your average load) then about 4KW of coolant heat are available (the generator itself is about 75% efficient so it takes more kw input than output). Some decent KW, but not nearly 20 KW as you suggest. And the thermostat controlled bypass will probably not allow all of the engine heat to go through the external heating loop. Some will go to the main heat exchanger.

So with that said, here are some comments on your three solutions. I presume from your comments that you have an existing diesel hydronic system.

1. Simple, but you probably need to pick the genset or the propulsion engine alone. Otherwise it gets much more complicated. You don't want to mix coolant from one engine in the other.

2. Elegant and workable. Run the coolant from the propulsion engine first to the calorifier and then to the plate heat exchanger. Finding a calorifier with three coils will be difficult (one for the hydronic loop and one for each engine). If you have to pick one, then run the genset coolant through the calorifier.

It will cost at least three thousand dollars for the main components and lots of labor and hose to hook up. You can buy a lot of diesel to run your hydronic system for that.

Diesel has 18,000 btu of heat content per lb (sorry, I will use English units) and a typical hydronic system converts 80% of that energy into hot water. The available 4KW from your genset is about 12,000 BTU/hr.

So to match the 12,000 btu available from you genset takes 12/(18*.8) = .8 lb/hr of diesel or .11 gph or 2.7 gallons per day. At $6/gal (I am using a relatively high number for Europe) that is $16 per day. If it costs you $3,000 to install the system then it will take about 200 days to pay for it. Unless you are wintering in N Europe it will take years to pay it out.

3. Not a good solution. You would have to combine your potable water with the heat circulating water. The heat circulating loop is often filled with glycol solution for freeze protection, so you could never do that. Probably takes a pump, check valves and as you said adaptation of the main heater controls to work.

David

[DeborahLee]

I taped into the engine cooling system. I put a "Y" valve in after the hot water heater and installed a school bus heater. I am like you I couldn't see burning more fuel for heat when I was already producing quit a few BTU's. With the "Y" valve I can shut it down during the summer months. IF the gen set is water cooled you should be able to valve that in when using it. You might want to google "Red Dot heaters" they have several different models in size and BTU's.

[Dockhead]

Thanks.

It occurred to me that this installation could be much simpler if I could find a multiple circuit plate heat exchanger. I don't know if such a thing exists, however.

[sailorchic34]

Just a quick note that the engine hot water pump is a very low head pump. So it may not have enough oomph to get water all that far from the engine. So if it does not work at first you may need to add a second heat exchanger with a pump for the space heating /water heating. Using larger pipe / hose will help reduce the head loss too. Hose has a rather large friction coefficient compared to pipe.

To get maximum heat from the engine you could use the main coolant hoses to a second heat exchanger inline with the main engine tank. Of course keeping the hose runs short would be important too. Then pipe off the second heat exchanger to the verious heating units with a pump and small expansion tank (could be overflow tank like on engine). That would give the most heating for the buck

[tom1263]

Not so easy, because there don't exist a special warm water boiler with enough connectors for cooling water circuit's, for more then one diesel engine.

Air handlers and all other stuff isn't the problem...

[Bash]

Originally Posted by Dockhead

How about something like this:

Attachment 66018

I had a system like that on my last boat, minus the generator. I added a "summer valve" that would bypass central heat manually if I just wanted to heat hot water when it was warm.

One trick with such a system is to run the water lines under walkways whenever possible so that you have nice warm floorboards in the mornings.

[Dockhead]

Originally Posted by tom1263

Not so easy, because there don't exist a special warm water boiler with enough connectors for cooling water circuit's, for more then one diesel engine.

Air handlers and all other stuff isn't the problem...

That's my Variant 3!!! Using the domestic hot water supply as a heat reservoir and exchange medium! So it's not just a crazy idea!

I know that calorifiers with three coils do exist, or can be made on special order. Might be cheaper and simpler than something with plate heat exchangers like Variant 2.

Hmmmm.

Edit: It's slightly different, upon closer examination -- the domestic hot water supply actually circulates through the fan coils. I've seen some heating systems (old fashioned, in Europe) which work like that. But I guess it works.

[tom1263]

I saw such a system from "webasto" on the "Boot" at Düsseldorf, i mean it's a normal warm water heating system for bigger boats. The advatage of a system with calorifiers is, you storing heating energy, whether you need, or not.