who has cogen

[elnav]

"the only thing i can think of is the generator has no thermostat, or they were afraid you would take the heat off the block like cars to for the cab heater. under such use it is possible to overcool the engine and in doing so the engine will start to smoke
pollute and coke/gum up quickly".

That is what I was figuring so I wrote back explaining how we planned to use a heat exchanger and separate circulation pump.   My guess is, it's a knee jerk reaction  by a manufacturer who has to ensure their engines are Type III compliant  and thus they cannot knowingly  advise on something that might  cause the engine to run outside the EPA mandated envelope.
The joke being this engine was shipped from Seattle to China  for installation and the boat will cruise away from North American or European ports  for the next five to ten years.
In other words  it will not even be in any place where  air pollution is taken seriously.

The expected cooling load for the boat is about 26,000 BTU or maybe 30,000 BTU.   I estimate we would not  be close to that for heating the same volume .  So how many BTU of heat could I reasonably expect  per HP developed  in the generator engine?

[Fat Charlie]

Never ask the factory what can be done- they'll fall back to the specs and never deviate because anything they say can and will be used against them.  They feel that the system dissipates heat well enough on its own, and that a modification to harvest that heat can damage the machine by taking more heat than the cooling system was designed to dump.  They know what happens next- "but Joe in your engineering department said it would be fine!"

Ask something specific that they can tell you without leaving their asses hanging out- like what temperature range the coolant return should be.  That and flow rate are all that the engine cares about.  For what it's worth, I'm not an engineer either. 

My system will go to a heat exchanger, with a shorter cutoff loop using a temperature control valve.  I haven't gone looking for said valve yet, but that's the plan.

[mobile_bob]

roughly speaking the following will give you an approximate value to answer your question

1kwatt = 3415btu's

so for each kwatt mechanical produced, the engine will dissipate approx 3415 btu's from the coolant and roughly the same
for the exhaust. the actual numbers will be about 3kbtu for cooling and 3kbtu for the exhaust for each kwatt of mechanical load
on the engine, the difference will be windage, radiation, vibration, noise and other minor losses.

so if you load the engine to 5kwatts electrical and maintain it there, and assume the generator is 80% efficient, the actual mechanical
load will be approx 5000 / .80 = 6250 watts mechanical load on the engine, so lets round it to 6kwatt mechanical

6000 x 3000btu = 18000 btus from the coolant and the same from the exhaust, is pretty close

therefore, 18kbtu + 18kbtu = 36kbtu available from both sources for harvest

i figure a recovery of approx 75% of that is attainable, so 36kbtu x .75 = 27kbtu's at 5kwatts electrical load

of course more load will produce more available and recovered heat from both sources, and conversely less load will reduce the available
and recoverable heat.

i think you will find my numbers are pretty close

bob g

[Fat Charlie]

Thank you, Bob.

That was the single most useful thing I've learned since August, when a friend explained his 6/1 to me.  Usually you're talking over my head, and that'll probably never stop- but today you helped me a lot.

Take care.

      -Ryan

[Lloyd]

Bob...

I'm sure your numbers are about as close as anyone will get. The fly in Enlav's case is that the NL is seawater cooled in a manicooler, so it will rob most of the recoverable heat, unless a bypass of the mani is set up.

I have been thinking about this issue, If I set up a seawater bypass of the mani, then I have no water to dump in the exhaxust. The connection between the mani and the exhaust elbo there is no room to set up a parallel bypass to feed just seawater to the exhaust. So I think, that the recovery will be scant.

So that leaves a bypass on the engine coolant side, which is ported to the mani, so that foils that plan. i think, it could supply domestic HW...but I'm not sure it could support cabin heat.

Lloyd

[mobile_bob]

i keep forgetting about those pesky marine watercooled manifolds, but
i suspect a good exchanger might get some heat, although not nearly what it would get without the
water jacketed manifold

if elnav could get a temp reading from right at the outlet of the manifold at 5kwatt electrical load
with seawater cooling of the manifold i think i could get a pretty good estimate as to how many btu's he has
left to take a run at harvesting.

that is unless the exhaust exits with the salt water waste from the manifold jacket, in which case there is nothing
i would want to try and harvest.



bob g

[Lloyd]

i keep forgetting about those pesky marine watercooled manifolds, but
i suspect a good exchanger might get some heat, although not nearly what it would get without the
water jacketed manifold

if elnav could get a temp reading from right at the outlet of the manifold at 5kwatt electrical load
with seawater cooling of the manifold i think i could get a pretty good estimate as to how many btu's he has
left to take a run at harvesting.

that is unless the exhaust exits with the salt water waste from the manifold jacket, in which case there is nothing
i would want to try and harvest.



bob g

yea Bob,

That is the issue, the tube bundle is floating so to speak in the the engine coolant, the engine coolant is ported to the block, into the manicooler, the Tstat is in in-between, so to stay above the Tstat you have to take the HW from the mani, and return through the pump.

The seawater is already harvesting most of  that heat, if you take supply of HW  from the block or the head you're bypassing the Tstat, and run the risk of over cooling the engine.

The mani dumps into the exhaust elbo in a 90. That requires you to fit the pre-made 90 hose as you fit the elbo to the mani...there is no way to replace the hose with-out removal of the elbo.

My guess would be to add a three phase tap to a storage tank with a three phase immersion heater, at least that way you would be able to run heat when the gen is lightly loaded and increase the total efficiency of what is typically an over sized Prime Power AC.

Lloyd

[Lloyd]

i keep forgetting about those pesky marine watercooled manifolds, but

bob g

That pesky mani can be a landlubbers friend applied to a co-gen...probably the most efficient way to recover the waste heat from both the exhaust and the radiator.

Lloyd

[elnav]

Lloyd,  This is what I am accustomed to seeing  in West coast boats.  I can only surmise the builder is playing CYA and the chinese yard is playing dumb. Neither is willing to say yes  meaning if  we design something and the yard  screws up, the blame falls  on the owner  who asked for the mod and myself.

My past exxperience with  chinese yards is not encouraging. The level of technical savvy is deplorable. 
If I specify a 15 amp breaker they ask what size wire gage. Duh!  They musxt have familiarity with 16A breakers since this is one of the standard sizes they use over there but they dont know what  wire to use.
I once looked up  the correct John Deere part number for a cast alternator bracket and verified all 6068 engine blocks were drilled to mount this bracket. The chinese yard came back saying it doesn't exist. 
And so it goes. 

[Ronmar]

FWIW:  For available heat, I have measured 16,200 BTU/HR out thru my cooling system heatexchanger with a 3KW electric load. That was a measured 3/4 GPM(6LB of water/min) raised from 77F to 122F(45F increase)  That is about 5400 BTU/HR per KW of electric load on the generator...  It was also right in line with the rule of thirds.  At that load I was burning a little less than 1/8gallon of fuel per hour, or about 50000 BTU worth of fuel.  1/3 of that fuel burnt is 16600 BTU...

YMMV.

[elnav]

Thanks guys for a lot of useful information.  I now see  the problem  in a better perspective.  Given the difficulty in communicating with a chinese boat building yard where the only english speaking person is a lady in the office who has no technical expertise and technical workers who can neither read, write or speak even one word of english  I think this option is effectively excluded  for this boat. However, the subject is definitely on the list of possible options for the future.

Being a newbie I have a dumb question.  Has anyone been able to make a workable heat recovery system for an air cooled engine.  Every  configuration I think of  soon reveals its flaws. Having been nearly killed by a VW  car heater system I  am extremely leery but  maybe there s a solution that had not been hought of back in 1980

[Lloyd]

Enlav,

if you can shroud the air cooling fins of the block/head...you could then adapt a air to water heat/x for the recovery without asphyxiation..

just a though

lloyd

[elnav]

Lloyd wrote:   

if you can shroud the air cooling fins of the block/head...you could then adapt a air to water heat/x for the recovery without asphyxiation..

That is exactly what Volkswagen did in their old air cooled motors and that is what almost killed me with CO poisoning on a long drive.  Fortunately a mechanic recognized the symptoms  before it was too late.  Most people might have mistaken the problem as being drunk.  I was once left  lying  near unconscious in a snow bank  after suffering a similar problem in another vehicle.   Needless to say I have little confidence  this approach is  safe or fool proof.

[Lloyd]

Enlav,

I think you misunderstood, there would never be any co as the it is seperate, the water can't carry co to the...you would be heating the water and then using the hw for domestic heat...I think the old vw's used air to air...just like the old Chev Corvair's.

Lloyd

[elnav]

Right you are but  how to make that shroud is still the challenge.  Getting a liquid tight fit  is just as bad if not worse than getting an air tight seal. Fischer Panda engineered a liquid cooled  generator and had nothing but  problemns  due to leaks.  The original air cooled genset was fine but converting it to liquid cooled  evidently proved  a real challenge.
I suppose you could blow the air past the fins then through a radiator for heat transfer in reverse.  Somehow it intuitively doesn't seem  to be  as efficient as having the cooling liquid directly in contact with the finned cylinder head.  Maybe the fins need to be cut back to give better  welding surface.