air cooled engine in cogeneration

[mobile_bob]

as an aside from the this thread
https://www.microcogen.info/index.php?topic=3658.msg40213#msg40213

the thought of using readily available air cooled engines in cogeneration

the problem historically with the use of air cooled, is the air cooled nature makes harvesting and using that heat source
problematic, making for a max. overall efficiency on the order of around 55-60% (mechanical and recovered heat of the exhaust)

several years back (around '07 or so) i came upon and purchased 3 telecom standby generator systems, they being 6kwatt 24volt nominal they look like little pizza huts or outdoor A/C compressor/condensor units. very well made using vertical shaft twin cylinder enigines belt driving the generator heads, well sound proofed and self contained, set to burn either propane or nat gas.

building on the other thread proposition

the thought comes to mind that for instance if we do the following

take a horizontal shaft engine like  used on a variety of lawnmowers, and other small equipment, say 20-25 hp or so
and to that we couple two A/C compressors and a direct drive generator head, put it all in an sealed enclosure, (by sealed i mean relatively, not perfectly)

in operation use on of the A/C compressors to remove the heat from within the enclosure, and move that heat to somewhere where it can be effectively used, space heating in cooler/cold months being most common usage.

the other A/C compressor could be used to drive a refrigerator/freezer, or to provide airconditioning for living space.
the generator for power production, whether AC or DC

the exhaust heat is recovered in the same manner as it would be on a water cooled engine to be used for domestic hot water, or space heating.

adding oil capacity is not a much of a problem

the unit could be made relatively small, and the overall efficiency would be comparable to other units in its class reaching well into the mid 80% range and maybe higher with good design.

the twin horizontal engine come self contained, so there is no need for wiring harnesses, computers and all the other stuff associated with car engines.

so you trade off the complexity of all the requisite stuff associated with car engines for an additional A/C compressor heat pump system?

might be a good trade off for some folks.
especially in colder climates where the systems heat supply could be put to good use.

and it might well be feasible in closely matched designs where instead of space heating the first compressor could move the heat from the interior of the enclosure through a plate exchanger to double up on domestic hot water production. make for more hot water for showers, dish and clothes washing.

i can visualize such a system that like described in the other thread, where it might be called upon to provide hot water and power in the early morning and evening for all loads described while also providing additional electrical power that is higher demand than the solar capacity one has on hand. 

my thinking is one probably wouldn't put up 10kwatts of solar if the average load is maybe 10-20% of that? and one might well not want the expense of a battery bank being sized larger to cover those times when you might need 10kwatt, but only for short durations?

apart from my horrendous A/C load in summer (46 year old central air, and i have no idea why i still runs, but does 24/7 about 5 months a year) my average power needs could be met with around 500watts of panels, but my short term (less than a half hour needs are on the order of 10 times that amount.

not considering the ridiculous A/C demands (anything would be an improvement) i could design a small system, well controlled and with load scheduling a system such as described and have it work quite well, and not have a need for several kwatts of panels, controllers, inverters and a large battery bank.

it would be easier with a water cooled engine, but i think with a bit of thinking not much more difficult to do with an aircooled engine, especially burning natural gas.

when i consider the local rate not just for the power per kwatt hour, but the demand charges, and all the other cool taxes and transmission costs they tack on, with natural gas i can compete favorably with the power company, save for a A/C costs ( and maybe those costs to if using natural gas, but maintenance costs will be much higher because of long operational hours, although absorption systems might mitigate this issue)

remembering of course, that traveling down this path one might not succeed, but likely will produce idea's and other things that have broader application.

just more of the stuff rattling around in my head

bob g

[DKMC]

What do you mean by 80% efficiency? Since the typical spark ignited gasoline engine is at most 25% overall efficient.

[mobile_bob]

thanks for the question

when i speak of 80% efficiency, i speak of overall efficiency

if we accept a gas engine as being 25% we know this is the amount of power in torque/rpm available at the crankshaft to do actual work, (making electricity in our discussion). the remaining 75% is a combination of heats lost do exhaust and cooling
(actually a bit less a small fraction is lost to convection, typically ~5%.)

so in cogeneration, we work to recover and "use" a large portion of the 75% of the heat from the exhaust and cooling system. it is not "too" difficult to recover 80% of the 75% waste heats, which adds approx 60% to the 25% typical mechanical efficiency for an aggregate total of 85% overall efficiency... i figure 80% as attainable overall.

now bearing in mind that we must actually capture/harvest 80% of the waste heats of exhaust and cooling systems, "and" actually put that heat to use offsetting heat we pay for do supply those needs.

commercially available cogen systems in our "weight class" (pseudo technical term) routinely attain an overall efficiency of 90%.  while this level might be difficult to attain for the average diy'er, 80% overall efficiency is in my opinion attainable.

hope this makes sense?

bob g

[DKMC]

I guess the basement makes a good location for the unit

[mobile_bob]

to expand a bit more

generally speaking, (also a trap i fell into) is the thinking that for cogeneration use the diesel has it over a gas engine
in bsfc or efficiency.

while it is true that the typical gas engine is approx 25% efficient and the typical diesel is a bit better than 30% (and higher in larger engine's) this is with more typical applications where we are only considering power output at the crankshaft being put to work driving a load, such as a car/truck or generator

if all we are going to use the prime mover for is turning a shaft then yes the diesel has higher efficiency and as such probably more desirable in most cases.

having gone down the rabbit hole of thinking i quit considering other prime movers (all gas engines) and summarily dismissed them for cogen use.

my mistake was in looking at the problem from a single viewpoint, rather than from all viewpoints

if we look at cogeneration from the end and look toward the front end, in that we look at what we are trying to get, being heat and power generation, and not have any preconceived thoughts from looking from the front end forward using best efficiency prime movers (best for what? cars/truck/generators).

if we look at either engine as a necessity, and consider them both to be much better at making heat than mechanical energy, and consider that we have need for and can use effectively this heat, then a much different picture starts to come into focus... at least it did for me.

taking all into account, there really is no advantage of one engine over another for cogeneration uses, (diesel vs. gas) apart from possible longevity issues, fuel long term stability in storage (no problem if propane or nat gas). and quite frankly i don't care if the two types differ in bsfc with crankshaft loads.

not sure if this makes sense?

thoughts ?
bob g

[mobile_bob]

i know there are cogen units made to be placed in the basement, however i don't feel comfortable in doing so
and as a diy'er it adds another level of safety concerns i don't feel are necessary.

given that fact that we can transfer electrical power just about any reasonable distance, and we can also move hot water over relatively reasonable distances as well, and refrigerants over similar distances. it would seem prudent to me to either purpose build a detached building or a non habited building like detached shop/garage.

i am thinking the typical insurance agent would be more comfortable with such a system in a stand alone purpose built building/shed well away from the house.

not sure i would argue with those that would be concerned with having fuel of any type in the basement, along with combustion gas leaks, crankcase fumes etc.  let alone vibration and noise.  even though each and all could be addressed and made safe, at an additional cost in dollars, time and effort.

i think i could build a shed for less dollars, time and effort, and sleep better for having done it.

bob g

[DKMC]

Sir, You may already have a Furnace and Water Heater in the basement proper already?
Both very capable arsonists and/or bombs. 

[mike90045]

Sir, You may already have a Furnace and Water Heater in the basement proper already?
Both very capable arsonists and/or bombs. 

A well designed furnace & water heater are quite simple and have had many safety features designed into them over the years

Diesel does not introduce "much" carbon monoxide", but a gasoline fueled engine does bring that added hazard  with it.

And bringing a IC engine introduces a lot more complexity and failure points beyond the existing hazards of heaters.  Coolant leak, belts, lots more vibration, overspeed or runaway.  Those things will make an insurance company nervous.

[glort]

Few random thoughts.....


Don't know what your experience with solar is bob but with 500W of panels I'd be flat out powering a tent.
You never get near the panels rating so if you want 500W of panels, Put up a Kw worth... at least! If you put up 4-6 Kw worth then you can be assured you will have your minimum requirement in pretty much any weather.  While overkill, it's far from uneconomical or non viable.
If you want 20 Kwh a day, different story.  
I recent'y read an article that added up all the losses from a 250W panel. the conclusion was one would get about 188W of power from it IF it were generating 250W in the first place which would be at very limited times.... if ever.  This takes into account wiring and inverter conversion in grid tie but I would assume an off grid charger would not be any better.

How much would you pay Per Kw for panels in your area new or used?

Here panels are regularly advertised for stupid prices. I have no idea where the people dream up these Ludacrous numbers, Often it seems on what they paid 10 years ago even though they have just had a new system installed and got their money back on the old one anyway. I like that. I put in a realistic offer which they dismiss as lowball.  I use other accounts to put in similar offers about once a week. I get back to them after a month and I get them sometimes less than I first offered.  What makes me really laugh is when they will advertise them cheaper than the first offer I made they told me to shove up my arse.
Don't go by what they are advertised for. You never know what they sold for but here it's rarely near the same thing.

With running the 2 X AC  Compressors, how many hours a day would you need the heating or cooling?
Granted, where I am I see some rather extreme temps but even on the average summer days, one  would still want to have the thing running a good 6 Hours a day minimum.
Much of that COULD be taken up by solar and save the engine wear and tear and fuel.
The benefit of running 10 Kw of panels would you would have your 500W for batteries and a couple of Kw for heating.

Even if you paid $100 Kw, that thousand dollars is going to last 10 years, probably 20 even on used panels and be basically maintence and hassle free with near no running costs once set up.
You will need an inverter and charger but they are getting cheap now too and should have a 5-10 Yr life time as well. With that sort of solar you could get away with the most basic engine as it's only going to be needed for extended bad weather so an unmodified engine using a straight alternator for topping up.  Might use 5L of petrol a year.

I have taken to " Heat sinking " the house.  Crank the heating through the day when there is solar so the walls and furniture are brought up to temp and are not acting like Ice bricks at night.  Same in summer. I found it much more economical to get onto the AC early so it's just keeping the temp rather than trying to pull it down once the heat has penetrated the walls and heated the furniture etc.
The other thing is the AC is Pulling from the day temp of around 20oC in the day as against  <5oC at night. makes a big Difference.


Idea for a small watercooled petrol engine..... 4 stroke outboard.
Don't know how much they go for in  your area, but they are getting cheaper here.  You can get them in whatever HP you want and may be able to pick up just a power head or one with a damaged gearbox etc.  
Other one might be a watercooled Motorcycle engine. Would have the advantage of the built in gearbox to make gearing the gen head even easier.

I wonder how well an aircooled engine could be made with oil cooling only? Take the fins off the flywheel and put a squirter in the engine casing firing up under the piston.  Maybe another port pouring oil up into the rocker area to keep the head cool.  Small external Oil pump and one could easily then put the oil though a HE like one would do with water.  Power steering pump could be easily modified to make flow rather than pressure but pressure only happens in restriction anyway. The casings are also ally so maybe put a squirter firing lots of oil to take away heat there too.  instead of putting the water externally, use the oil internally.  The exhaust could be jacketed and use the oil through there too before it goes to the HE.
An larger engine  like an 18 HP under driven say 50% would give more surface area internally for the oil to take the heat away.  Maybe a Piece of aluminium Tube could be brazed around the head where the cooling fins go if internal oil cooling wasn't enough.

This would be an easy way to increase sump capacity and just plumb in an external oil filter.

On that thought> I wonder how much the life of a basic air-cooled China " Predator" type engine would be increased buy having it's blood put through a proper Filter? Far as I know, it's only the  22 Hp and larger twin engines that have a proper spin on filter so something that does not have any filter may benefit in extended life quite an amount.

These small aircooled China engines are cheap enough to muck around with and spares are so readily and cheaply available, it would be hard to experiment and have a total loss anyway.

[mobile_bob]

Sir, You may already have a Furnace and Water Heater in the basement proper already?
Both very capable arsonists and/or bombs. 

quite true, however both are UL listed and backed by companies my insurance carrier will underwrite
and with deeper pockets for me to sue should either cause me or mine harm.

i don't really want to shoulder those burdens all by myself.

[mobile_bob]

Glort

your argument in support of solar panels is not lost on me, certainly they have come down in price sufficiently to make them
very attractive indeed,

perhaps the innate desire to discuss combustion engines comes on the heals of having worked on, maintained, overhauled, basically ate, slept and breathed diesel engines for all of my adult life (which is near 50 years now) i have gotten so much grimey oil on my skin that it has absorbed into the fabric of my being and i have become part machine? 

at this point, it is clear to me that i am not making my case clear enough to understand, so maybe i will take a pause, rethink/regroup/repackage the theory (or hypothesis) and make another run at it.

bob g

[glort]

Sorry If I am being obtuse  Bob.
It is not intentional, Just unfortunate on my part.  :0(

[mobile_bob]

Glort

no problem,  the fault is likely mine in that this is something i have given an enormous amount of thought to over
the last 20 odd years.

however there is a huge difference in "giving thought" to something and actually "sitting down" and doing the calculations.

and all this based on accepting it as a given that there is a need.

i had a pleasant discussion on the phone today with a fellow member of the forum, and the bottom line or take away from that conversation was the realization (even though it would appear as obvious in hind site) we are all creatures of our environment.

here in the states prior to 2005, listeroids and chanfa diesels were widely available at affordable prices, and because of this most of us gave little thought to any other prime mover, let alone doing any serious analysis into other means of power production like solar.  solar was historically very expensive and we just continued to accept that as fact, even though used panels were available for around 2 bucks a watt at that time.

in england, canada and some other countries that were under englands influence such as Oz and NZ, most folks looked to original listers and petter engines as their prime movers of choice.

it is not sure that there were not at the same time some country somewhere on the planet where flathead fords still were available and that is what folks there would gravitate to. (ok, this might be a slight exaggeration)

having said that it is a sure bet that the listeroid/petteroids are very common and first choice in india, while the changfa types are very popular in china and other parts of the orient.

basically "ya run whatcha brung"

and building on the basis of those that don't adapt perish, as it relates to the USA and specifically this forum
if we don't adapt we will perish or become irrelevant, i think we have had our period of grieving over the EPA ban
and it is time to adapt and start thinking about what else can we do to adapt.

surely now that solar has gotten so cheap (i am now aware of at least one source of used panels at 75 bucks per 175 watt panel (which is but a fraction of what used panels were bringing in 2005 at about what? 40 odd cents per watt)

however if we still accept there is a desire if not a need for a generator, beit for backup, battery charging, cogen or whatever, then we must adapt and it seems prudent to see what other girls came to this dance we find ourselves attending.

the aircooled engines such as harbor freights predator engines are about as low in cost per hp as anything ever was, they seem to be relatively good value, certainly good enough for prototype work and likely cost effective in the long run, so they seem to be at least one example of aircooled engines that are available to those of us here in the states.

the water cooled automotive engine also is widely available here in the states as well, however a bit more complex to work with admittedly.  i am not sure of how tow auctions work over all the differing states, however i do know how it works in washington state. Tow companies must hold a car for i think 90day (no more than 6 months) and then are allowed to hold an auction to sell the car, the original owner is barred from bidding.  a guy that is reasonably good with cars, or has a mechanic buddy can take a look at the car and determine if the powerplant looks to be viable and reasonably well maintained and then stand his ground and attend the auction.  unless you are going for some popular car, most will bring no more than their weight per ton to a salvage company.  i have bought two different caddy's (one with a 472 the other a 500cu/in) for 15 and 25 bucks respectively, the nissan i mentioned earlier i gave 25 bucks for.  all three had excellent engines.

but i digress (yes again)

one of the driving reasons for going down this path that i have chosen, is one of exploration, experimentation and exploration (cousins of why some folks climb mountains).

those that spend their lives seeking to always learn i think will understand, while those that abhor learning might well find it very difficult to understand.

some folks are driven in a direction that they cannot explain, other then they derive pleasure from doing it.
while other watch on shaking their heads thinking "is that guy crazy or what?"

and i am as guilty as anyone in that!  i know of at least one friend that likes to skydive and is passionate about it, while there is no friggin way on earth i am going out the door of an airplane that is moving let alone off the ground even a foot!
give me the yoke! i am going to exhaust all possible outcomes before i take that leap.

does that make the other guy crazy? no! does that make me somehow more intelligent? no!  actually it might be argued that i am the ignorant one, as i am too close minded to even entertain discussion about jumping out of the plane in the first place, and the other guy the smarter as he has spent the time to learn something new, that just might have broader application (even though i remain steadfastly ignorant). 

then i wonder the following

how i might react, or rather how any of us would react if we were to go down into the basement and take our first in depth look at our natural gas furnace, taking off the side covers and finding a 4" long 1" keyed shaft sticking out the side turning at 1800rpm! (with a coverplate with a label stating "mechanical waste")... i am thinking there would not be a single one of us so ignorant as to not at least want an explanation of what this could be used for?  and what if we found it to truly be a waste product that could be harvested and produce 3kwatts or more?

would we not then be talking about all the possible uses of this waste product, and wouldn't we view our lowly furnace in a much different light? i think i for one surely would! as i would be also thinking "hmmmm, how can i use this waste product to do useful work, while also using the primary product (heat)?

i realize this is a simplistic and frankly ridiculous analogy, however lets turn it around

what if a guy having never seen an internal combustion engine, or a gas furnace, while having nat/gas to cook with and living in a cold climate was presented with for instance a small engine (we know it as an engine, he does not) this engine has a cover over the crankshaft pto,  he connects it to nat/gas and starts it up, to find "hey this thing puts out heat, and alot of it"  and "dang this feels nice in my house"  so he sets out to figure out how best to use this new fangled heat source that he refers to as his new furnace (furnace is a word he knows as he already heats with his wood fired furnace that he has to chop wood for).

now imagine his surprise when one day while working on his new furnace he removes that cover and finds that crankshaft pto!  (lets say he is living in relative dark and while he has solar panels and batteries, it is cloudy and he has to peddle a bicycle to recharge them).

i am thinking that this guy is going to take about a new york minute to at least start the process of thinking how he could adapt his new furnace pto shaft to his peddle generator, negating his need to exercise and laying awake nights thinking of how he might use this new source of waste mechanical work, what implications there might be in using it, how he might effectively use the excess primary heat of the furnace, and if it would be worth the effort, the economics etc.

lastly there is this to consider

say for instance and accepting that in almost every case, power from the grid is cheaper than we can produce it.  the question then becomes how much more expensive is producing my own power? is it an affordable difference? am i willing to pay the difference and lastly am i getting something else for the added cost? ( the justification for doing this)

for some the analysis dies at the break even point, or short of it, "hell if i don't save money i ain't doing it" is one guys thinking,

while "hmmm, it looks like this will end up costing me about 100 bucks more a month than if i continue to buy from the power company, and i find this acceptable as this is the cost of my hobby and i can always take a month off if i like to lower or control this cost",

while still another might well think " yes this will end up costing me 100 bucks per month over just paying the power company, however the education i will receive is worth far more than that to me"

i know lots of guys that spend far more than this amount of money each and every month on beer! and while they may feel smarter the more of it they drink, i think that is certainly arguable.  throw in cigarettes and it becomes very hard for some to understand.

so yes, it might well cost more to do cogen than to simply buy more panels and batteries, i think the gains are worth the additional cost. 

and just in case this explanation still falls short...

while one can arc weld with solar panels, i think most see the wisdom of having a portable gas drive welder to negate that need.