Comments on: DOE: Combined Heat and Power a compelling but underutilized source of energy efficiency

By: Standard Electrical Dictionary - Q | Offshore Electrician

Standard Electrical Dictionary - Q | Offshore Electrician — Tue, 16 Dec 2008 11:30:45 +0000

[...] DOE: Combined Heat and Power a compelling but underutilized source … [...]

By: J.C., Sr.

J.C., Sr. — Fri, 05 Dec 2008 01:28:06 +0000

I’m retired now and no longer own my own home. My wife and I owned a home for many years with first oil and then natural gas fired forced warm air furnace. The heat going out that flu used to drive me nuts. Only lately have I read anything about Stirling engines. It seems to me that you could use that heat using a heat exchanger as Tim mentioned to run a 12 volt generator to power the same power motor to run the blower or pump if you have baseboard heat. That way your furnace would be at least independant of outside electrical power. No one ever thought of those things years ago because all energy was dirt cheap.

By: miggs

miggs — Thu, 04 Dec 2008 18:34:34 +0000

Like you said at the end, a lot of folks who read this blog know about waste energy recovery, but in the U.S., few people do, including the experts. I’m associated with Recycled Energy Development, probably the leading CHP company here in the States. Actually, by our calculations, cutting greenhouse gases by 20% would be the equivalent of removing EVERY car from the road, not half. Either way, there’s an awful lot of potential here, mainly low-hanging fruit.

By: tim

tim — Wed, 03 Dec 2008 23:09:55 +0000

There’s only one thing that reduces the practicality of CHP on a domestic scale: noise.

I’ve puzzled for some time over the absurdity of burning virgin fuel (natural gas in our case) to produce low-grade heat in order to make a house habitable in winter. There is just so much low-grade heat produced as waste… but not in the right place.

The power station 300km away that produces electricity to light my lights and run my fridge releases plumes of steam and torrents of warm water from its cooling towers. But it’s wasteful enough getting the electricity from there to here, let alone the low-grade heat.

My not-really-a-plan was to repurpose an old car engine to heat my house. Shaft power from the engine would turn a generator to produce electricity; coolant would run to a remote “radiator” in my heating ducts. A heat exchanger on the exhaust could also reclaim heat. The engine and coolant hoses could be insulated to ensure all “waste” heat was rejected through the coolant into the house.

It’s not especially difficult to run a spark-ignition engine on natural gas, especially if it is to provide steady-state power with no throttle response required. Efficiency of the engine would be quite irrelevant. If it’s running efficiently it will produce more shaft power (electricity) and less heat, if it’s running inefficiently it will produce more heat and less electricity. Either option is better than my existing furnace which produces all heat and no electricity – the limit case of an inefficient generator.

Emissions are a consideration, but not a blocker. We’re already burning gas for domestic heating in cities, so as long as we maintain a similar quality of combustion for similar grade of emissions there will be no big change.

Aside from time (so many projects so little time), the main blocker to this plan is the noise of the engine. I don’t want a piston engine droning away under my house. A stationary engine running at a fixed speed could be silenced more effectively than in a car, but it would be very difficult to muffle enough to be unnoticeable at 3am. The engine needs to be close to the house to make effective use of the waste heat (long coolant hoses from a distant generator shed would lose most of the heat en route, even if well insulated – an inherent problem with low-grade heat).

Domestic-scale CHP would be a great step forward in efficiency, but would require some serious thought in terms of noise. Nobody wants to live next door to a power station, for the same reason that they wouldn’t want a domestic-scale power station in their basement.