Energy efficiency conversion 4

[containerwall]

I have pondered the idea of the total btu release from gasoline or propane being ignited by spark or burnt in flame. It seems to me to use an internal combustion engine to create both torque and heat would be superior to simply burning it. The torque energy could power alternators, generators, and compressors. The radiator could be replaced by circulating hot water into a radiant slab, the engine heat from the manifold could be cooled immersing that in water also. There need not be any btu's escaping unharnessed. Is this a good idea or am I missing something? What would the net btu utilization be compared to a furnace or boiler? A horizontally opposed two cylinder engine like the old Subarus may work best?

 

[GregLocock]

Roughly 50 years ago Fiat proposed natural gas powered engines for large buildings, generating electricity and hot water. In my opinion the numbers don't add up compared with solar, but obviously that depends on your cost for fossil fuel.

Cheers

Greg Locock


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[Hoxton123]

This is called 'combined heat and power' (CHP) or CoGeneration.

Nothing new. Google it.

 

[gruntguru]

Honda marketed a marvellous little CHP for home use. In cold climates they offer significant savings over a typical electricity-grid/oil-or-gas-heater solution.
Link

je suis charlie

 

[hydrae]

I have often thought that space heating should be the waste heat from and engine, get the high grade heat
in the form of motive power then send the waste heat to the building (home, office, industry)
The first 2 require an engine that is without even a moderate amount of noise or vibration.
Even the best built ICE engine is not be something people want to live next to.
Thermo electric generator is one option.
A Stirling engine is the other.
Sadly neither of these technologies have proven out to make sense economically at scale, yet.

On the maintenance side of things, your off the shelf Subaru Engine if used as you describe would need an
oil change every week and a rebuild every year

Hydrae

 

[TugboatEng]

Using CHP doesn't make much sense for heating because a simple furnace is already nearly 100% efficient. It does work for cooling, though because the waste heat can drive saturation type refrigeration cycles.

 

[BrianPetersen]

Well, high-grade energy in the form of electricity is of greater value than low-grade energy in the form of heat. Depending on what your local utility pays small-scale generators, the thinking back then is that even if the cogeneration had to use (lets say) 50% more natural gas than a furnace would in order to produce the same amount of heat, the value in selling the (more valuable) electricity back to the utility potentially covers the cost of the natural gas.

There's another way to do this, and I know it's done in Scandinavia: District heating. The electrical generation plant for the town is located close enough to the town that the heated water it produces is pumped through another water distribution network to buildings in town and used for heating.

It doesn't appear that small-scale cogeneration (to replace your central furnace) ever got off the ground.

 

[Hoxton123]

The ratio between the cost of electricity and the cost of fuel in energy terms must be greater than 3:1 for CHP to 'work', as a general rule.

There are lots of factors, like with any industrial purchase, such as capital cost, maintenance cost etc.

With maintenance, the labour cost does not fall as the kw falls!

So, with conventional natural gas fuelled CHP it is difficult to make a case for small units, say < 200 kw or so.

There are a lot around in Europe and North America. Here in England, most hospitals have a CHP set, for example. With sewage works and other digester systems, the fuel is essentially ‘free’, so they have long been an advocate of CHP. The ‘waste’ heat from the engine is used to heat up the digestate.

Car derived engines have long been out of favour, like the Fiat Totem units mentioned earlier. They are just not constructed for the long base load operation.
Remember that if your car’s average speed is 40 mph say, then you get to 100,000 miles in 2500 hours. That’s about 15 weeks! I know the car engine duty can be affected by stop start driving etc.

Truck engine derived units can be ok, but for larger units you get into proper industrial engines like Cummins and Caterpillar make.

 

[Lou Scannon]

Truck engine derived units can be ok, but for larger units you get into proper industrial engines like Cummins and Caterpillar make.

...and even some non-US companies

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[Hoxton123]

Lou
Yes I know, but the OP used the term BTU, which strangely marks him as American!

By the way, a ship can be thought of as a CHP set if it has reciprocating engines. I have never seen a radiator on a ship!

 

[TugboatEng]

This is what the radiator on a ship looks like.

However, motor ships do often have waste heat boilers in their stacks. I have also seen engine cooling water used to boil water in evaporators.

 

[Hoxton123]

Plate heat exchanger.

The term radiator like in a car, is not really correct as the heat exchange is more by removing hot air from around the fins, I believe. Air blast cooler is a better term.

Ships using heavy fuel oil (HFO) as fuel have exhaust steam boilers, in my experience to heat the fuel and trace heat all the piping.

For those who don’t know, HFO can have a very low pour point, 35 C or so. Essentially solid at room temperature, like tar.

In CHP, the ‘power’ does not have to be electrical, it can be mechanical, like on a ship or a pump or compressor drive.

 

[RodRico]

Is this a good idea or am I missing something?

It's a great idea, which is why it's been done. You are missing something, however; the emphasis has moved from efficiency to emissions. Solar is terribly inefficient, but it has a practically infinite supply of clean fuel. Where fossil fuels remain unmatched is in airborne transport, and the opportunity for cogeneration is extremely limited in that application. At some point, airborne transport will switch to more costly carbon neutral and engineered fuels to reduce its carbon footprint.

 

[enginesrus]

All carbon base fuels are essentially carbon neutral. Since at one time it was all free carbon that became chemically joined to form a molecule. Man has added nothing new to the earth, he has manipulated some elements, but there is nothing new under the sun. For the planet earth mineral oil is carbon neutral.

 

[GregLocock]

Yes, but before the ffs were generated the CO2 content of the atmosphere was ~7000 ppm, about 17 times what it is today. One of the few solid bits of evidence that agrees with the current religion that thinks CO2 is the thermostat is that the global average temperature was quite a bit hotter than today.

Cheers

Greg Locock


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[RodRico]

All carbon base fuels are essentially carbon neutral. Since at one time it was all free carbon that became chemically joined to form a molecule. Man has added nothing new to the earth, he has manipulated some elements, but there is nothing new under the sun. For the planet earth mineral oil is carbon neutral.

Yes, the entire universe is "natural" so we don't need to worry about nuclear waste, chemical pollution, poisons, or anything else, right? When someone says "carbon neutral" they mean "over a short period of time." Unleashing carbon sequestered over millions of years in only a hundred years results in rapid climate change. Of course some will say "climate change is natural; it's been happening continuously since the earth was formed." That's true, but it usually happens very slowly and life has time to adapt. When life doesn't have time to adapt, the consequences can be quite unpleasant. The disruption when a billion people flee floods, drought, and famine will have significant socio-economic impact and may lead to war. Of course some will say "war is natural"...