Micro Cogeneration for a Large Sailboat

[Dockhead]

Hi guys:

I stumbled across this site looking for information about home-built generators.  I spent many happy hours browsing through threads, and was amazed at the wealth of knowledge on here.  We sailors also share a lot of technical knowledge and experience among ourselves, and since power production on board is one of the biggest technical things we have to deal with,  a lot of people have a lot of knowledge and experience.  But I have to say, you guys are in a class of your own!!

So I thought I would describe my system and see if any of you has any insight.

My boat is really off-grid as I keep her on a mid-river mooring in the Hamble, South Coast of England, with no shore power, and usually stay at anchor when out cruising.  I spend about 90 days a year on board and 50+ sea days, so it is a well-used second home for me as well as a boat.  Our summer cruise this year took us through the Chenal du Four and the Raz de Sein into the Bay of Biscay and South Brittany.  Next year we hope to make it to the Orkney Islands and on to Iceland.

I generate electrical power with a Kohler 6.5EFOZ, which is a heavy duty low-speed continuous duty genset which produces up to 6.5kW of single phase power at 230 volts and 50 hertz.  It is powered by a 1000cc three-cylinder Yanmar running at 1500 RPM.  The genset lives inside a sound enclosure inside a sound-proofed engine room, so is easy to live with - inaudible from outside the boat and just a pleasant murmer inside.

My house electrical system is 24 volts nominal.  I have a battery bank of 420 amp/hours, deep cycle Trojans
which I charge with a Victron Multiplus charger inverter, capable of charging at 70 amps (x 24 volts), and with 2500 watts of inverter power.  This is a nice unit for off-grid life because all the AC power on board runs through it, and you can set it so that it limits the power draw from any given source, shore power, or generator.  When the demand on board for AC power exceeds the limit you set, then the Victron will supplement the shore power or genset power with inverted power taken from the batteries.  It effectively "peak shaves", which allows you to live comfortably on a limited AC power source like, for example, the shaky shore power we get sometimes (sometimes only 6 amps in France!). 

My batteries are also charged with a 100 amp (* 24 volts) Leece-Neville school bus alternator on my main engine, which is externally regulated with an Adverc regulator.  This is nice, because whenever we move, if any motoring at all is involved, we arrive with topped up batteries.  Also I can invert a couple of kW of AC power while the main engine is running, without drawing on the batteries, which is also great.

So the situation with electrical power on board is already pretty good.  With five people on board, in the summer time with no heat going, I often don't need to generate power more than once a day for two or three hours.  And we use a fair amount of electrical power with a huge proliferation of portable devices on board (phones, tablets, laptops), kitchen appliances, lighting, AV, washer-dryer, etc.  – we're not roughing it.  I think it's costing me less than electrical bills to a utility would cost, as the genset only uses 1.5 liters per hour of diesel fuel at half load and costs almost nothing to maintain (oil and filter every 100 hours is about it).  Despite paying around 1 quid per liter for the fuel, about $6 per U.S. gallon.


So far so good.  The real problem is heat.  Up here above 50 degrees latitude, we may need heat in any month of the year, and are for sure heating nine months out of the year.  We do have a hydronic central heating system based on a 10kW Eberspaecher (Espar) diesel fuel burning furnace, with three fan coils.  But besides diesel fuel, this system uses a fair amount of electrical power, meaning we can't get away with just one generator run a day when we're heating. 

This system also heats domestic hot water through a coil in the calorifier (marine hot water heater).  Domestic hot water is also heated by a second coil through which coolant from the main engine is run, and from a 1.5kW immersion heater.  I often heat domestic hot water with this immersion heater run off generator power, which is wasteful, but I usually prefer this to firing up the central heating system if I'm not space heating.  On the other hand, sometimes it's good to add some load to the generator, which doesn't like to run lightly loaded.

And yet at the same time, I am dumping vast amounts of waste heat into the ocean whenever I use the main engine or generator.  As a rule of thumb, for every kW of mechanical power produced by a diesel engine, you are producing 1kW of heat into the cooling system, and another 1kW of heat which goes out the exhaust.  This offends my sense of engineering elegance, and so I want to do something about it.

Namely, I want to get main engine waste heat into the heating system, or into a separate system of space heating, and I want to get generator waste heat into heating as well.

Here are a few variants I've thought of:

1.   Simple.  Tap the generator cooling circuit and install three-way solenoid valves (three port, two position)  in the main engine coolant loop which runs through my calorifier, so that  I can switch that loop over to my genset when I'm generating.  Install a booster pump in that loop to be sure that I'm getting circulation through the generator (I don't know where to tap it, so that it will circulate by itself, and I'm not sure the fresh water pump is strong enough anyway to get the coolant all the through the calorifier, some 6 meters away).  Install another booster pump in the central heating loop which goes through the calorifier, to boost the transfer of heat out of the calorifier and into the central heating system, when the calorifier is already hot from the main engine or generator.

This has a drawback in that a small amount of coolant will be commingled between main engine and generator, which you are technically not supposed to do.  But I use exactly the same coolant in both, frequently changed, so I doubt that this will actually do any harm.

I am hoping – in this variant -- that the calorifier will serve as a kind of heat storage and heat exchange system between the engine, generator, and central heating system.  I know that depends on the surface area of the loops inside the calorifier, which I don't know, and on the flow of coolant through the various heat sources (but I would plan to boost them all).

One sub-variant of this:  Mount a school bus heater in the return side of the main engine cooling loop, and position this under the companionway stairs.  This will allow me to directly space heat when the main engine or generator is running, using whatever heat is left over after heating domestic hot water.  This will only heat one space, the main saloon, and not the whole boat as the main hydronic heating system does, but it's a simple solution, and simple is good.


2.   More elaborate.  Install a plate-type heat exchanger in the main engine coolant loop which runs through the calorifier, and run generator coolant through this heat exchanger.  The heat exchanger would go on the supply side of the loop so that it would heat the calorifier first (otherwise it would be heating the main engine).  Add booster pumps to both loops.  This would prevent the commingling of coolant.

3.   Most elaborate.  Install two plate-type heat exchangers in the main engine coolant loop which runs through the calorifier.  Run generator coolant through one, and run the central heating main return pipe through the other.   Install three-way solenoid valves in the main engine coolant loop so that the engine itself can be bypassed (otherwise the whole system will be constantly heating up the engine).  Install three booster pumps – in the central heating return pipe (to make up for resistance of the heat exchanger and extra pipe), in the engine coolant return pump (when the engine is bypassed, there is no other way to circulate coolant), and in the generator coolant loop.


This variant will transfer heat from main engine or generator to the central heat return pipe, so not depending on the calorifier to work as a heat storage and heat exchanger.  I am guessing that this will be much more effective in getting heat into the central heating system, and with a separate switch for the pumps, I might be able to heat without the Eberspaecher furnace working at all.  Even if the furnace is working, it will automatically modulate down, using less fuel, if it is getting warm enough water from the return pipe – it only needs to add whatever heat is not enough after the heat which comes from engine or generator. 

I like the fact that this variant is calorifier-centric – all heat goes through a loop which goes through the calorifier.  That will make it efficient in heating domestic hot water when no space heating is required, which is a priority.

But I'm not sure about the mini-loop that will result when the main engine is bypassed.  I guess I will have to put a header tank in there.  I'm not sure how that will interact with the main engine cooling system.

The other drawback of this variant is that it will be fairly complicated and expensive to implement.  I doubt whether it will pay for itself compared to just running the central heat a bit more.  It is not a requirement that whatever I do should pay for itself, necessarily, but it would be nice.

What do you guys think?

[thomasonw]

Hello.   Funny how a few of us 'boaters' end up here - but there are a lot in common between our goals.

In your quest to pull heat from the generator, you also might look into the archives on some folks efforts around exhaust heat exchangers.  if you are able to reroute your exhaust system (safely, keeping in mind fire hazards) you might be able to pull some more heat before the cooling water injector.  (I am assuming you have a wet exhaust system)

On your three 'options' a couple of things I considered in my setup:

1) I really do not like to run the mains engine coolant all over the place.  Every tap, pipe, bend, etc. is a point of failure that I like to keep down.  Now, we are a 'trawler' type boat, so a bit more dependent on our engine, but still - myself:  I am using a heat-exchanger located next to the mains to keep those critical sections as tight as possible.  Then take it into the existing hydronic system to be routed to either space heating radiators, and/or the domestica water heater loop.

2) You might also want to consider failures and health issues.  There is a school of though that one should NOT have only a single walled heat exchanger between engine coolant and domestic drinking water sources - and yes, those coolant taps on hot water heaters breaks this...    In my case I have a two step system - so to speak:  the 1st being the localized heat exchanger next to the engine that couples from the engine coolant into the hydronic system, and then a 2nd isolation at the hot water heater coolant ports.  By monitoring water levels in each of these closed loop systems I hope I can notice a single failure before it starts killing us..

Some simple snap-type thermostats and if needed small hot-water rated boosting pumps is all that is needed.

We typical spend 8 months a year away from the docks, so having a simple and robust system is critical to us.  Well, that, plus backups ala the electric heating element!   Will be interesting to see what you come up with, and do hope you post it back here!

-al-

[Dockhead]

Hello.   Funny how a few of us 'boaters' end up here - but there are a lot in common between our goals.

In your quest to pull heat from the generator, you also might look into the archives on some folks efforts around exhaust heat exchangers.  if you are able to reroute your exhaust system (safely, keeping in mind fire hazards) you might be able to pull some more heat before the cooling water injector.  (I am assuming you have a wet exhaust system)

On your three 'options' a couple of things I considered in my setup:

1) I really do not like to run the mains engine coolant all over the place.  Every tap, pipe, bend, etc. is a point of failure that I like to keep down.  Now, we are a 'trawler' type boat, so a bit more dependent on our engine, but still - myself:  I am using a heat-exchanger located next to the mains to keep those critical sections as tight as possible.  Then take it into the existing hydronic system to be routed to either space heating radiators, and/or the domestica water heater loop.

2) You might also want to consider failures and health issues.  There is a school of though that one should NOT have only a single walled heat exchanger between engine coolant and domestic drinking water sources - and yes, those coolant taps on hot water heaters breaks this...    In my case I have a two step system - so to speak:  the 1st being the localized heat exchanger next to the engine that couples from the engine coolant into the hydronic system, and then a 2nd isolation at the hot water heater coolant ports.  By monitoring water levels in each of these closed loop systems I hope I can notice a single failure before it starts killing us..

Some simple snap-type thermostats and if needed small hot-water rated boosting pumps is all that is needed.

We typical spend 8 months a year away from the docks, so having a simple and robust system is critical to us.  Well, that, plus backups ala the electric heating element!   Will be interesting to see what you come up with, and do hope you post it back here!

-al-

OK, thanks.  So I take away from this two things -- 1.  heat exhange main engine waste heat into the hydronic main loop to keep the engine coolant loop short.  I guess same thing applies to the generator.  2.  worry about engine coolant in the calorifier.  I'm not really concerned about 2, for a couple of reasons: (a) we don't drink domestic hot water; (b) there is a non-return valve to keep the domestic hot water from back flowing into the fresh water system; and (c) the boat was built like this (like very many boats).

I guess I could leave my system the way it is, put in two heat exchangers -- one main engine loop to hydronic loop (on the return side , after the calorifier), the other generator to hydronic. 

Hmm. 

The only problem is I can't make domestic hot water from generator waste heat without heating the whole hydronic system. 

I guess in order to reduce the complexity of circuits circulating coolant water from engine and generator, I could just heat exchange the generator waste heat into the engine coolant loop.  It wouldn't be as efficient, since I will be heating up the main engine all the time, but if the  heat exchanger is in the supply side of that loop, it should be better.  It will be simpler with fewer points of failure, and the generator coolant loop will be vastly shorter.  Hmm.

To think about the amount of heat at stake:  Kohler says that this genset gives off 7.9 kW of heat at full load.   See: http://www.maesco.com/products/kohler/kohler_diesel/G2052.pdf   If we think that rejected heat is proportional to fuel consumption, then the genset should be putting out 4.75 kW of heat at half load.  Now I can't recover all of it, since that's the whole temperature rise from the coolant operating temperture (about 70 degrees C) and the seawater (about 10 degrees C, usually).  But still, two or three kW of heat is very significant -- enough to heat the boat at moderate outsid etemperatures, and certainly enough to make hot water.

[thomasonw]

<<SNIP>

The only problem is I can't make domestic hot water from generator waste heat without heating the whole hydronic system. 

<SNIP>

Hi, not sure how your hydronic setup is, but in my case we have the space heating loops 'switchable out' and inactive during the summer.  Then some simple insulation on the rest of the plumbing.  In this way, during hot-water heating (aka Summer) only the boiler and the pipes to and from the hot water heater are warm.   The Hurricane brand boiler we are using has a selectable mode to run everything, except the actual fuel oil burner.  During 'co-gen' mode (either from the generator, or the mains) we select this mode and let the mains engine and/or the generator be the heat source.  Everything else is unchanged, pumps, etc.   And again, during summer only the supply pipes and the 'boiler' (which is now just an insulated hot water tank in its own right) get warm.

With this approach, we can ALSO redirect heat into space heating by using the existing hydronic cabin space heating elements if we want (ala, while underway).  Just turn off the 'summer loop' mode.

Not sure if this helps or not, I guess as a overview:

Our hydronic system is a loop containing the boiler, turnouts for the mains heat exchanger, and the (to be installed) generator heat exchanger.  These three act as heat sources and if all were active would be in series.  (btw, loop flow has the mains and generator heat exchange in the boiler RETURN line, to let the mains/gen pre-heat water as they can, and let the boiler - unless it is 'turned off' top off the temperature).   

This loop then continues to supply heating needs.  There are 4 'zones', all in parallel .  One 'zone' is the domestic hot water heating taps on the hot water heater and is always active.  The remaining three zones have individual on/off valves for space heating in each of the three major areas in the boat.  Each zone is selectable on or off,  and that is actually how we control 'summer' vs 'winter' mode.

So in operations, the things to be heated (hot water, space) take in the heated water, and we have three sources to heat the water:  Boiler, mains, and/or generator.  The turnout for the mains / generator heat exchangers are controlled via snap-switch thermostats located on the local heat exchangers, so they only open if
1) There is a call for heat and
2) The associated heat exchanger is warm enough to give anything meaningful.

This keeps us from extracting too much heat and over cooling things...

Oh, and one other thing:  We depend on our systems for 8 months out of the year, coming into dock only during the winter (say November .. Feb).  When I installed the hydronic system I did NOT use 'marine' 12v devices, ala 12v pumps, valves.  Instead I used equipment typically installed in domestic (residential) and small office systems.   24v AC turnouts, and a 120v AC circulator pump. Built up a relay box to convert the 12v signals from the Hurricane boiler to drive this.   I am sure uses a bit more energy (need to add in the Inverter losses as well), but hydronic heating is not a new technology, been around for a LONG time, so figured I would use a proven approach.  Too much of what  seems to  sold as 'marine quality' is design with the knowledge that most boats see perhaps 2-3 weeks TOPS of usage a year....  (Learned that one real well after going through 3 sets of domestic water pumps, just died after a year of full time use..). 

Again, hope this is somewhat clear and give you some ideas....   Best of luck!


-al-

[Dockhead]

Thanks very much for that, very interesting!

A couple of great ideas I got from you right off the bat:

1.  Put in solenoid valves to cut off the main heating loop, for summer operation.  Maybe just one valve on the supply side.
2.  Put in a switch to run the circulation of the main hydronic system without the furnace operating.

Your system differs from ours in that you have only one coil in your calorifier.  So you've just cut in heat exchangers for engine and generator cooling loops, transferring heat into the return loop of the hydronic systems water heating branch.

My system has separate coils for engine coolant and for the hydronic system's water heating branch.  I could just block off the engine coil and rig mine up like yours, but I don't think I really want to -- the plumbing would be somewhat awkward.

HOWEVER, you gave me a great idea -- I could just leave the engine loop the way it is, and install just one single heat exchanger -- cutting in the generator cooling loop into the return side of my hydronic system, the water heating branch, like yours.  I think that piping runs under the sole next to the engine room and shouldn't be too bad.  If I have a solenoid valve to cut off the main heating loop, then I won't be heating up the whole hydronic system with the generator waste heat.  Great idea!!


So this starts to look rather elegant.  my modifications would consist of:

1.  Tap into generator cooling circuit and bring generator coolant to a plate type heat exchanger.
2.  Plumb the plate type heat exchanger into the return loop of the hydronic system, water heating branch.
3.  Install a booster pump in the hydronic heating water heating branch to overcome resistance of the heat exchanger.
4.  Install a booster pump in the generator coolant loop.

5.  Install a solenoid valve in the supply pipe of the space heating loop of the hydronic system, to allow me to go into "summer mode"
6.  Install a switch to allow me to run the huydronic main pump without the furnace being on (or maybe the booster pump would be enough by itself.

Hah, I like it!!!!

[Lloyd]

Thanks very much for that, very interesting!

A couple of great ideas I got from you right off the bat:

1.  Put in solenoid valves to cut off the main heating loop, for summer operation.  Maybe just one valve on the supply side.
2.  Put in a switch to run the circulation of the main hydronic system without the furnace operating.

Your system differs from ours in that you have only one coil in your calorifier.  So you've just cut in heat exchangers for engine and generator cooling loops, transferring heat into the return loop of the hydronic systems water heating branch.

My system has separate coils for engine coolant and for the hydronic system's water heating branch.  I could just block off the engine coil and rig mine up like yours, but I don't think I really want to -- the plumbing would be somewhat awkward.

HOWEVER, you gave me a great idea -- I could just leave the engine loop the way it is, and install just one single heat exchanger -- cutting in the generator cooling loop into the return side of my hydronic system, the water heating branch, like yours.  I think that piping runs under the sole next to the engine room and shouldn't be too bad.  If I have a solenoid valve to cut off the main heating loop, then I won't be heating up the whole hydronic system with the generator waste heat.  Great idea!!


So this starts to look rather elegant.  my modifications would consist of:

1.  Tap into generator cooling circuit and bring generator coolant to a plate type heat exchanger.
2.  Plumb the plate type heat exchanger into the return loop of the hydronic system, water heating branch.
3.  Install a booster pump in the hydronic heating water heating branch to overcome resistance of the heat exchanger.
4.  Install a booster pump in the generator coolant loop.

5.  Install a solenoid valve in the supply pipe of the space heating loop of the hydronic system, to allow me to go into "summer mode"
6.  Install a switch to allow me to run the huydronic main pump without the furnace being on (or maybe the booster pump would be enough by itself.

Hah, I like it!!!!

You Dockhead,

coming from Lloyd, aka "FlyingCloud 1937"

Turn off.........all off you preconceived ideas, when you, want to learn something new.

Lloyd

[thomasonw]

Thanks very much for that, very interesting!

A couple of great ideas I got from you right off the bat:

1.  Put in solenoid valves to cut off the main heating loop, for summer operation.  Maybe just one valve on the supply side.
2.  Put in a switch to run the circulation of the main hydronic system without the furnace operating.

Your system differs from ours in that you have only one coil in your calorifier.  So you've just cut in heat exchangers for engine and generator cooling loops, transferring heat into the return loop of the hydronic systems water heating branch.

My system has separate coils for engine coolant and for the hydronic system's water heating branch.  I could just block off the engine coil and rig mine up like yours, but I don't think I really want to -- the plumbing would be somewhat awkward.

HOWEVER, you gave me a great idea -- I could just leave the engine loop the way it is, and install just one single heat exchanger -- cutting in the generator cooling loop into the return side of my hydronic system, the water heating branch, like yours.  I think that piping runs under the sole next to the engine room and shouldn't be too bad.  If I have a solenoid valve to cut off the main heating loop, then I won't be heating up the whole hydronic system with the generator waste heat.  Great idea!!


So this starts to look rather elegant.  my modifications would consist of:

1.  Tap into generator cooling circuit and bring generator coolant to a plate type heat exchanger.
2.  Plumb the plate type heat exchanger into the return loop of the hydronic system, water heating branch.
3.  Install a booster pump in the hydronic heating water heating branch to overcome resistance of the heat exchanger.
4.  Install a booster pump in the generator coolant loop.

5.  Install a solenoid valve in the supply pipe of the space heating loop of the hydronic system, to allow me to go into "summer mode"
6.  Install a switch to allow me to run the huydronic main pump without the furnace being on (or maybe the booster pump would be enough by itself.

Hah, I like it!!!!

Well...  Um.   Ah. . .  ok. . .




So, I have been away for a while, to a place where the internet do not shine :-)    But am back in the 'connected world'!

Dockhead: sounds like you got some good ideas here, and a handle on an approach for modifications!  Great!  Not sure you will need a boost pump in the hydronic loop, providing you can use the existing circulation pump in the heater?  ala, on the Hurricane that is the feature it has where we tell it to let everything work as normal, pumps, zone controls, etc.  Just do not fire the burner...   Perhaps you heater has a like capability, or if not, as you mentioned you might need to add some extra hardware...

FYI:  Here is an example of the 3-way turnout I have used:  http://www.honeywelluk.com/products/Valves/Motorised-Valves/V4073A-Motorised-Midposition-Diverter-Valve/

They come with different attachments (flare, solder, FPTs), and I found mine on Ebay for under $30 each.  I use the 2 port version for turning on and off the zones.  You just need 24v AC to power them, but it sounds like you likely have that covered on your boat already...

Oh, one more idea for you - independent of tieing in the generator..   If you install another plate type heat exchanger into the two inlets for the hot water heater  (Domestic cold water in, as well as hydronic hot-water in), then this will 'pre-heat' the domestic hot water before it gets into the tank.  It in effect turns the whole system into an instant hot water heater!   We did this before our little 5-gallon hot-water tank.  It takes about 5 minutes for the Hurricane to come up to temperature, but once it does we have unlimited hot water!   During a test run I let the shower run on nothing but HOT for 25 minutes, and never was there any drop in the water temp.   Soo nice - as when we are heating water using electricity, that 5-gallon tank only lasts about 5 minutes or so    


Hey, best of luck with your mods -don't forget to look around and see if you can find anything on the exhaust heat exchangers some folks have done - if that can safely be done on your boat you might be able to pull a bit more energy from the generator before the exhaust mixer...

-al-