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27 Apr 2006
While following the links provided alongside a very interesting article on how to reduce household energy consumption in A-to-B magazine, I came across some information about highly efficient, power generating domestic boilers which contained Stirling engines, and I wondered again why we don’t see Stirling engines everywhere. Why did VHS (steam power and then the infernal internal combustion engine) win?
I first learnt about Stirling engines several years ago on a TV programme (who says TV isn’t educational?) and marvelled at their elegant design. Invented by Rev. Robert Stirling in 1816, the Stirling engine was intended as a safer, quieter and cleaner alternative to steam power. But modern Stirling engines using modern materials can even be more efficient than many petrol or diesel engines.
The principle is fairly simple; the cylinders are sealed and contain a fluid (usually a low molecular weight gas like hydrogen or helium), and contain a piston. One end of the cylinder chamber is heated externally, expanding the gas. This causes the piston to rise up, but as the opposite end of the cylinder is cooled, the gas compresses again, returning the piston to its starting position. So all you really need is to create a temperature gradient from one end of the cylinder to the other. The engine is quiet because there are no explosions going on inside the cylinders, and the components can be much lighter and simpler because no combustion happens inside the cylinder and it doesn’t need an air intake or exhaust or complicated fuel valves. The process is extremely efficient, and because it just needs a source of heat (or coolness!) rather than something to combust, you can run a Stirling engine on gas, oil, solar energy, geothermal energy, waste methane from landfill sites or even the heat from a cup of coffee.
Unfortunately, Stirling engines aren’t really suited to road vehicles (though there is a lot of interest in using them in aircraft) because of the size of the heat exchangers needed, and because they take a little while to get going. However, they do make excellent domestic boilers. New micro-CHP boilers use Stirling engines running on gas or oil to generate hot water for radiators and taps, and also cleverly use the moving piston to generate a small amount of electricity, which can either be used in the home or sold back to the grid. It’s true that it’s not renewable energy, but the micro-CHP boilers are supposed to reduce emissions by about 25% over a conventional combi-boiler. That could make a huge difference if all new homes were fitted with them, and people were encouraged by subsidies to replace old boilers with micro-CHP units.
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Hmm - what happened there? it should have read:
by Jonathan Briggs @ 27/04/2006 9:04 pm • Permalink •
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Jonathan Briggs: You know, I actually started to think about how you might use a heat pump to power a Stirling engine, which would in turn power a heat pump, and now I have a headache. Ground source heat pumps are very interesting though. I wonder how much they cost to install?
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More than you'd save in a lifetime! About £14,000!
by Jonathan Briggs @ 29/04/2006 7:05 pm • Permalink •
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Why would you get a headache?
You have a heat to motion to electric power system, where part of the electric output is feed back into the system to improve efficiency and/or decrease the cost of the total system.
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Jonathan Briggs: Eeek!
Gnoll110: It was a joke. I was thinking about it and conjured some kind of impossible perpetual motion machine up; a kind of Escher engine.
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bsag. The idea of a heat pump Stirling engine is not a joke but a perfectly valid proposition.
All machines are 100 percent energy efficient. No energy is lost ever to the Universe due to the laws of energy conservation.
In a car for instance 80 percent of the energy comes out as heat and 20 percent comes out as useful work. No energy is lost.
In a heat pump Stirling engine the temperature differential created by the heat pump would drive the Stirling engine.
Heat pumps can be made with a COP (Coefficient Of Performance of more than 6)
That means that WE only have to put in a sixth of what WE get out. All heat pumps are 100 percent energy efficient. No more or less energy comes out than is put in. The difference is that WE only have to put in a small amount of energy.
The Earth is actually very warm due to our Sun shining on it for billions of years. Without our Sun the earth would be a cold dark planet with a temperature close to 0 deg Kelvin (- 273 deg C) The ground temperature in the UK is about + 285 deg Kelvin which is HOT. This is free energy.
So a ground source heat pump connected to an efficient Stirling engine which powered the heat pump compressor would work and produce surplus free energy. It would run either until the Earth ended its life or it wore out!
Free energy is a reality. On a sunny day stand in the sunshine and feel the free energy pouring down on you! The beauty of using ground source heat is that is still there when the sun goes down.
by Arnie @ 08/04/2008 7:49 pm • Permalink •
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Maybe you could use a Stirling Engine to power a <a>Heat Pump</a>.htm - sort of extracting sunbeams from cucumbers!
by Jonathan Briggs @ 27/04/2006 9:04 pm • Permalink •