Honda EU2000 as chp base?

[TimSR2]

I've been shopping for a portable suitcase generator for use at the marina, and for charging rv batteries ( through my 120v smart charger of course.!) While shopping on ebay,  I have found yamaha and honda units in the 1600 watt continuous/2k peak range for under $1000, and propane/ng conversion kits for another $200 or so. So it's possible to buy a top quality, inverter, long run capable, auto throttle,  high efficiency genset with  tri-fuel capability for 1000 to 1200 dollars!  Sound levels  at WOT under 55 db for both manufacturers.   Under 50 pounds and self contained with rubber vibration isolating feet,  ready to go to work.

These  generators  all seem to intake their  cooling air at the genhead /inverter end, and exhaust the waste heat out the exhaust pipe end...... lending themselves easily to a combined generator/exhaust/engine cooling air  to water  heat exchanger system.  I'm thinking 3 or 4 passes, stacked , electric fan assisted.  Stand the generator with the exhaust facing the heatex and pull the cord and go.  The heatex would be about the same width as the generator, but twice as long and 4 or 5 times taller. Exhaust gases vented out the top through a vent at the eaves of the building

If efficient heatex design can be worked out, we could move up to electric start units ( 3kw up) , and have remote controls.

I've seen so many threads  seeking a chp base unit that is small, water cooled, governed, etc.  I think the answer is in front of our faces here.  With off the shelf top quality inverter genset converted to gaseous fuel  being available 'off the shelf' ,  the only engineering challenge is to overcome the 'water-cooled' bias and design an efficient  air to water heat exchanger. If properly done the portable gensets could be swapped out for service with no tools; only the fuel connection would need to be changed.  The heatex would be  much larger than with water cooled units, of course.  

Advantages:  

late model hardware!
easy interchangeability of complete packaged generator units
easy to obtain parts
single, unified heat exchange system
tri fuel capability
super quiet operation, no diesel knock
proven long life of "driver units"
low oil shutdown standard, breakers standard.
Head unit, inverter, all AC connections UL/CSA approved
pure sine AC power output
The portable power unit would always be available for camping, or off site use, or resale.
The non  corrosive exhaust would permit a combined heatex to be built of aluminum or even regular steel, with low degradation due to corrosion or carbon buildup

Disadvantages:

It's not a diesel  (get over it!)  Spark engines produce more waste heat so all is not lost.
This probably needs a really big heat exchanger system .


I haven't really done the surface area math properly yet but, lets just say at 85000 btu/ gallon for propane, at 28 pct mechanical efficiency, that leaves 61000 btu available for extraction.  At just 50 percent efficiency that's 30,500btu per gallon free heat.  Enough to raise 305 pounds of water by 100 degrees fahrenheit in about 3.5 hours, even at this relatively low efficiency.    At full load these units are .28 gallon /hr  so should be able to supply all your domestic hot water and most  of heating needs..  Natural Gas is about a third the price of propane!  



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[BioHazard]

I have my doubts about efficiency, but would definately be interested in seeing a workable hot air to water heat exchanger. If you could figure that part out you could use most any "consumer" generator. I've always wondered if the EU2000 could be grid tied the same way you can use it in parallel with another generator.

It's all just a matter of cash I guess, Honda makes some pretty nice water cooled RV gens that would be a great "off the shelf" start to a CHP system. Big money though.

[Ronmar]

I would be interested in the heatex also.  With the high volume airflow required to keep an air cooled engine cool, I think you are going to need a heatex with a very large surface area to get any real efficiency.  You will also need proper flow control to allow the air to spread out and turbulate in contact with the transfer surface. 

Had opportunity to use 2 large EU gensets for a project we were doing at work.  Cool units, and I was thinking the same thing.  With proper and VERY carefull ducting to separate the exhaust, that heat could be sent into a dwelling to heat it directly, or under the floor of a cabin to warm the floors.  But with a possible exhaust leak being a problem, it would be safer to transfer the heat to water, but again, that is a high volume of air to harvest heat from...  Nice to stand around on a chilly morning with all that warm air dumping out the end though...

[BioHazard]

But with a possible exhaust leak being a problem, it would be safer to transfer the heat to water, but again, that is a high volume of air to harvest heat from...

I don't think the idea of an exhaust leak is that big of a deal(as long as you don't do a half assed job)...even a commercial furnace is just a small crack away from getting exhaust into the heated air. I'm starting to wonder how well an air cooled engine could directly heat a dwelling, but would probably be better suited to something like my shop than a house.

As always, CO detectors would be a must.

[Tom Reed]

Why not just start with an RV generator. They already have a ducted outlet that can be plumbed directly into household vent system. Remote start/stop is already there too.

[TimSR2]

Because the little air cooled units are about 1/4 of the price. Light weight, and interchangeable..  Also  the generator and inverter waste heat and exhaust heat are all in the same stream, and one could easily locate the system  battery charger inside the heat exchanger to maximize the total heat efficiency of the design. The air cooled off the shelf  generator  inverter units offer a unique opportunity to harvest the entire  mechanical /electrical loss waste heat stream in  a one design heat exchanger system.    

[David Baillie]

I've been thinking on this one for a while.  My latest plan is to use the in house coil off of an air to air heatpump built into a metal box to give the air from the engine plenty of dwell time.  My onan 4.4 combines the engine heat and exhaust into one stream and I just don't know enough to know what would happen if I altered the back pressure by attaching something to just the exhaust.  I assume that all that extra air from the engine cooling would mean the heated water would be too cool for hydronic but probably fine for dumping into a slab for radiant?  Not sure.  Like the idea of off the shelf components but I don't know if a Honda EU would be cheaper then an RV unit.  My ONAN off of a utility truck with 600hrs on the clock only cost $400.  Generac 50 units seem to be less then $2000; close to the cost of a  EU 3000 but made to be put into close comfinement, and soundproofed.  Just some thoughts
David

[cujet]

On my Cessna, the cabin heat is taken from the outside of the muffler. A simple cabin CO detector is the only indication of a leak. 40 years down the road, no leaks! While it's a high quality, well designed, 321 stainless muffler setup, and the heat is taken only from an unwelded outer section. It's certainly a viable method.

My point is this, you could easily review muffler quality, installation and sealing qualities. And, if the muffler was not an unnecessary risk, configure the system to duct all the engine's heat, and some of the exhaust's heat taken from around the muffler. Add a welded tailpipe and duct the clean air down a PVC or flex pipe. However, it would be my guess that the muffler would not be a perfectly sealed unit, probably thinly constructed for light weight.

You do run the risk of other "engine smells" upon initial startup. But, those can be managed by not drawing heat until the system is warmed up. Just thinking aloud here, but some of the air could be used to keep any possible exhaust leak exiting out some other outlet. Using a variation of a  double walled pipe.

The problem with such a setup is that you must honestly assess your abilities and capability to keep exhaust out of your heating air.

There are "tried and true methods" Using one of those "proper methods" would be the only way of assuring acceptable safety.