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Old 11-09-14, 04:15 PM   #8
F357
Helper EcoRenovator
 
Join Date: Sep 2014
Location: Oregon
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Quote:
Originally Posted by jeff5may View Post
Converting heat to mechanical or electrical energy is very inefficient. If your goal is to provide heating and cooling, an ammonia or lithium bromide absorption system is the most efficient.
Except components for such a small system are nearly non existent. Compressor heat pump stuff is often available for less than scrap price. Also the ammonia needed is highly poisonous so that doesn't seem like something that should go into a homebrewed system.

Quote:
Originally Posted by jeff5may View Post
a condensing furnace or boiler combined with a heat recovery unit on the exhaust pipe is more efficient.
How do you figure? Is that more than 200% efficient?

A cogenerator is not a money saving device at $1.01 per therm. A natural gas heat pump just might be, if I can find a compressor that is efficient enough, and if any of my numbers above are even remotely close. It is also very hard to collect 100% of the waste heat from a cogenerator, if you are not using a refrigeration compressor. (Small water cooled generators or engines with governors are very very expensive and hard to find) To make electricity at these gas prices would cost about 40% more than buying it.

If my math is correct it is cheaper to run a natural gas engine than it is to spin an electric motor of the same size, even if you throw away all the heat. But in a heat pump situation, that heat is very valuable.

I can tell you for a fact that York used to build and sell a gas heat pump like this, that was roughly 3-5 tons for household use in the 80s/90s. It is no longer in production, and I don't know why. Maybe it wasn't efficient enough. Or maybe there was just too much maintenance keeping the engine running. Or maybe the EPA killed it for some reason...

Last edited by F357; 11-09-14 at 05:25 PM..
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