It's called "cogeneration", and it has been done in the past, including at a small-scale household level. It has never caught on.

Small combustion engines need maintenance, and I'm not sure the average homeowner would want to give their furnace periodic oil changes. The run-time hours also quickly add up. It could easily see 1000 hours of engine-running time in a heating season. That's like driving 60,000 km in a car. 5 years is like 300,000 km of driving. Is this going to be worth an overhaul every few years?

A heat pump is better ... electrically driven and all. If you live in a climate that warrants having air conditioning, you already have the expensive bit of this - and the cogeneration system will still need not only its own expensive piece (engine) but still need that air-conditioning compressor.

I should add that district-heating is used in quite a few small towns in Europe (Denmark for sure). Town has a central electrical generating station, heated water from the condenser is pumped through pipes underground and supplied to buildings for their interior heating.

Micro turbines with foil bearings eliminate the oil change and maintenance problems. They can run absorption cycle refrigeration or provide heat. Probably a better option than a gas engine. Then again, a turbine is a type of engine.

Several decades ago we used the coolant for a large diesel engine as process heat - and also ran a generator off the diesel to provide 240V for a bank of immersion heaters to increase the rapidity with which the coolant warmed.

Cheers

Greg Locock


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In theory yes, but if what you want is heat then efficiency of a condensing gas boiler can be over 90%.

Or do you mean gasoline?

If you want / need electricity that's fine but then you only get heat when you want electricity - doesn't always happen unless you have a decent battery storage system, but then you get electricity and no heat.

Also sometimes (spring / summer) you want electricity but you don't want heat, or not a lot. What do you do then? Your efficiency then drops back to a standard engine of 30-35%

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My concern comes from working on air cooled engines in aircraft, where CO poisoning and related accident deaths are not a trivial occurrence.

Eventually, exhaust pipes will corrode.

Eventually, a concrete slab may seep CO into the house or other structure.

Eventually, someone may die without even knowing what happened to them.

Don't do the exhaust pipe in the slab. Divert as much of the exhaust heat to the coolant as possible with a heat exchanger, then make sure that you vent the exhaust to the atmosphere away from (or above) the dwelling.

Municipal recip-powered cogeneration is pretty common in remote towns and cities that arent connected to a major grid. I've been to 1MW+ site in northern N America, Europe, and Asia as well as the Caribbean. Waste heat is typically extracted from the cooling loop via a heat exchanger and separate circuit with its own pump, then used to heat buildings, provide hot water, or condensed for water purification and industrial purposes.

Recip power generation in the USA is very rare. It's not emissions friendly at large scale and too expensive at small scsle. I only know of digester gas disposal for recip power generation at a MW scale but it's still only a few MW per unit. Basically, they're inexpensive engines run to death as they get paid to burn the gas.

Exhaust pipe in the slab is a bad idea for safety reasons as turbomotor says. It is also a bad idea to cool the exhaust below dew point before exiting the pipework.

je suis charlie

For CHP / Cogeneration, first stab is to determine the lowest heat demand, then do the same for electrical demand.

object is to select a set which will run 24/7 at max power, without exporting electricity (unless you get a good price).

Heat can be taken from the exhaust down to a temperature of 120C for natural gas, 150C for biogas, to keep the full exhusr run above the dew point as earlier stated. Jacket water heat can also be recovered, but not all intercooler heat, as second stage intercooler has to low a temperature to use.

Quote (TugboatEng)

Recip power generation in the USA is very rare. It's not emissions friendly at large scale and too expensive at small scsle. I only know of digester gas disposal for recip power generation at a MW scale but it's still only a few MW per unit. Basically, they're inexpensive engines run to death as they get paid to burn the gas.

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It is used extensively in many Alaskan towns.

It's quite extensive actually, and not only with biogas. It is increasing actually, as a counterbalance to so-called renewable energy that cannot always be called up on demand when needed. Also, many installations such as data centers use such engines, not only as backup power, but for revenue generating peak shaving, as a profitable means of investing in reciprocating backup power.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

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Question? How to do qoutes on this forum?

je suis charlie

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