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Termyn8or -> RE: Natural gas- ? more of the house on it? (4/23/2010 10:46:00 PM)
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If you like AC and having a fridge, gas can be used to run them. Usually there is some help from electricity, in the form of circulating fans and such. But the biggest draw, which is the compressor, is eliminated. The absorption system is the only way known at the moment to pump heat without a pump that moves a refrigerant, which to be efficient needs a high latent heat.
The absoption system is expensive initially, but it has some serious advantages. Actually a refrigerator can be made to run completely by gas, by just using convection for the air movement. It usually works well because for the sealed system to function it usually must be kept pretty close to level. This can keep your food cold. Since it has to stay level anyway, using convection works because the designer can depend on gravity and the atmosphere.
However for AC you need power. You need to pump air. So it will not get you off the grid despite the fact that either can be rejetted for propane and run off of tanks. They still do sell refrigertors that run propane for use in campers and such. The same principles of operation apply, but if you want AC you have to force air. To stay off electricity you need a source of power for the fans. Convection works fine in a box, but not in a house.
If you really want to stay away from electricity, the Stirling cycle engine could be used for the fans. Actually though it is not all that efficient, it is perfectly suited for the purpose, but I don't think you can buy a system like that to my knowledge at this time. Also bear in mind that these flame powered refrigeration systems are not cheap. And they are not free to run (*). A gas powered cooling system of normal proportions will have a burner similar in size to what a stove has, slightly small maybe. But remember it cycles on and off.
* they can concievably be run off solar power since heat is the actual fuel
Which does bring me to an esoterical question : I have asserted that here is a difference between an engine and a motor. Possibly not quite correct but illustative is the point that you cannot roll your car down a hill, running the engine backwards which by theory would extract the pollution from the air, reconstitute the fuel and pump it back into the tank. Now the Stirling cycle engine might turn out to be a motor instead, in that if you took the place you heat to make it run and make it cold instead it would run backwards and instead of using and dissipating heat energy it would gather it from the ambient and become exothermic rather than endothermic, at least on the input side. A Stirling works mainly on a heat differential and it is possible, but I am not able to say that it is. Nor can I say that a Stirling could pump heat if the shaft was rotated by external means. Therefore I cannot declare it a motor rather than an engine.
OK, now go get high everyone, I know this is too much.
T
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