Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 14/02/2012 16:26:22
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What about domestic gas boilers? Could we scale down TEGs technology to a domestic level?
Asked by Jim Robertson
Visit the webpage for the podcast in which this question is answered. (http://www.thenakedscientists.com/HTML/podcasts/show/20120212/)
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We answered this question on the show...
Andrew - Domestic gas boilers, I suspect, would probably not be a particularly good use for thermoelectrics because thermoelectrics are inherently very inefficient at the moment, maybe 5%.
However, if you take something like a wood burning stove, the primary purpose of that is to produce heat in the room and if you covered the surface of the stove with thermo electric material, you could generate a certain amount of electrical energy from the heat transfer through the thermoelectrics. In other words, the primary purpose of the stove is to heat the room and the heat going through the thermoelectrics does that but you can convert a percentage of that into electricity.
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The protective devices on a gas fired boiler that ensure that the pilot light is burning use a small TEG
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Although I'm not disagreeing with the experts conclusions (that it may not be practical) the reason he gives is not correct.
I mean presumably you would want to interpose in some way the TEG between the gas burner and the hot water/central heating loop; using that as the cold sink and the gas flames as the hot source.
The thing is, any inefficiency of TEGs is irrelevant in this application because the inefficient waste heat just goes into the hot water system, which is the point of the boiler anyway(!); so this is a classic CHP (Combined Heat and Power) scenario.
Any electrically energy you did generate would be about 3x more efficient and lower cost than at a conventional power station, since they don't usually do CHP there, they just have big chimneys for their waste heat, but you would be using your waste heat for hot water and heating.
I do see practical problems with the fact that TEGs are apparently insulators though. You need to be able to transfer the heat into the water as easily as possible.
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Yes, it's a pity we can't capture the waste heat our car produces and take it home to heat our house! It would make an enormous dent in our heating bill if we could.
I suppose if we had a really long hose.........
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You can:
Electric car, generator in the basement, waste heat into the heating/hot water system!
The problem is things like noise; genies are noisy!
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The Russians many years ago marketed a thermoelectric generator that fitted to the top of the glass of an oil lamp that could produce enough power to run a simple transistor radio.
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You can:
Electric car, generator in the basement, waste heat into the heating/hot water system!
I know of an even better way, but I won't be able to tell you about it until we file the patent!
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Obviously you don't want to use electric resistance derived heat to generate electric energy, otherwise it would be like a dog chasing its tail.
However, I would think the trick, would be to configure your TEGs so that the heat passing through them is not lost. So, for example, if you had ducting passing through a living space, you could "insulate" the ductwork with TEGs. You would have a low temperature gradient, but the heat lost through the TEGs would just go into the room which you desire to heat anyway.
The TEG would likely decrease the temperature of the heat being released into the house slightly (blown and leaking through ducts). However, even if the TEG was only 1 or 2% efficient, that decrease in temperature from the TEGs would be 100% converted into electricity, which is better than the power company does with their power generation.
Let's see what Geezer thinks about using ductwork TEGs with Heatpump or AC heating/cooling. Actually, it would do well with AC because you are leaking warm air from the room into the cold air stream, and removing energy in the process, so your net should be MORE Cooling. But, it may actually also increase the efficiency of the heatpump for heating.
However, I'm not considering a huge net gain of energy in a residential setting. So, sorry, you might as well leave the EV in the garage and ride the bicycle.