A thought on efficiency
A thought on efficiency
(OP)
A thought on energy efficiency:
There are quite a few houses that are heated with natural gas, right now if the furnace is brand new it is 90% efficient, older 70%.
Is there an engine out there that is very quiet, extremely reliable such that it could run a 50% duty cycle for year between services and a decade between overhauls?
This engine could be installed inside a heat exchanger that would extract the heat from both the cooling system and exhaust to heat the house.
Now you are taking fuel and turning it into useful work and heat. You are still getting between 70% and 90% of the useful heat into the house plus maybe turning that electric meter backwards.
OK tear this apart, why is nobody doing this?
Hydrae
There are quite a few houses that are heated with natural gas, right now if the furnace is brand new it is 90% efficient, older 70%.
Is there an engine out there that is very quiet, extremely reliable such that it could run a 50% duty cycle for year between services and a decade between overhauls?
This engine could be installed inside a heat exchanger that would extract the heat from both the cooling system and exhaust to heat the house.
Now you are taking fuel and turning it into useful work and heat. You are still getting between 70% and 90% of the useful heat into the house plus maybe turning that electric meter backwards.
OK tear this apart, why is nobody doing this?
Hydrae





RE: A thought on efficiency
RE: A thought on efficiency
- Steve
RE: A thought on efficiency
Second time I saw it was when I built it, large diesel engine supplied process power and heat for an agricultural installation. Warm up time was accelerated by using immersion heaters in the cooling system.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: A thought on efficiency
RE: A thought on efficiency
http://www.marathonengine.com/cogeneration.html
http://www.energytomorrow.org/Cogeneration.aspx
http://www.theoildrum.com/node/3723
http://www.cogeneration.org/
RE: A thought on efficiency
RE: A thought on efficiency
http:/
RE: A thought on efficiency
Thus, they exist (as others have noted), but they are not in general use because they are more expensive and most people don't need the portability and grid independence.
RE: A thought on efficiency
um, cogeneration?
RE: A thought on efficiency
Not sure what you're saying here exactly. I'm talking about individual cogeneration units versus basic grid power. For efficiency in terms of kwh/$$, individual cogeneration cannot compete. If you're talking about industrial cogeneration units, I didn't read that as what the OP was about, and I believe that is in fact being done. I probably agree with whatever your were trying to say.
RE: A thought on efficiency
For some isolated areas where cheep energy is not available, residential cogeneration might make sense.
RE: A thought on efficiency
http://w
A brochure I have shows 290W -> 100W plant/outlet loss from the grid vs. 118W -> 100W CHP/outlet loss from their system.
Fuel price volatility may be another variable that makes innovation tough for residential application. Last year oil was 2X gas in cost- don't know how coal stacks up, but who can predict where those will fall over the payback period for an unconventional residential system?
RE: A thought on efficiency
Zapster - if by "most" you mean "less than 8% of production" then you're probably right. Perhaps we should all define our terms more carefully.
RE: A thought on efficiency
RE: A thought on efficiency
To quote from several internet sources:
http://en.wikipedia.org/wiki/Cogeneration
By 1978, Congress recognized that efficiency at central power plants had stagnated and sought to encourage improved efficiency with the Public Utility Regulatory Policies Act (PURPA), which encouraged utilities to buy power from other energy producers. Cogeneration plants proliferated, soon producing about 8 percent of all energy in the U.S.[13] However, the bill left implementation and enforcement up to individual states, resulting in little or nothing being done in many parts of the country.
http://www.cogenworks.com/gtf_didyouknow.html
Although cogeneration has been in use for nearly a century, in the mid-1980s relatively low natural gas prices made it a widely attractive alternative for new power generation. In fact, gas-fired cogeneration is largely responsible for the decline in conventional power plant construction that occurred in North America during the 1980s. Cogeneration accounted for a large proportion of all new power plant capacity built in North America during much of the period in the late 1980s and early 1990s.
"The average efficiency of fossil-fueled power plants in the U.S. is 33% and has remained virtually unchanged for 40 years. This means that two-thirds of the energy in the fuel is lost–vented as heat–at most power plants in the United States. CHP systems achieve effective electrical efficiencies of 50% to 70%. This improvement in efficiency is an excellent pollution prevention strategy that reduces emissions of air pollutants and carbon dioxide, the leading greenhouse gas associated with climate change."
http://www.epa.gov/chp/markets/index.html
htt
Combined heat and power (CHP) offers many benefits over separate heat and power for a wide variety of applications and users, such as: Industrial manufacturers
Institutions Commercial buildings Municipalities residential structures
Some sectors are well-suited to expand their use of CHP because: (1) CHP technology is a strong technical fit for these facilities' needs; and (2) CHP systems can potentially generate significant bottom-line cost savings for these industries and organizations.
Is My Facility a Good Candidate for CHP?
If you answer "yes" to 3 or more of these of these questions, your facility may be good candidate for CHP.
Do you pay more than $0.06/kilowatt hour (kWh) on average for electricity (including generation, transmission, and distribution)? Are you concerned about the impact of current or future energy costs? Is your facility located in a deregulated electricity market? Are you concerned about power reliability? Does your facility operate more than 5,000 hours per year? Do you have thermal loads throughout the year (including steam, hot water, chilled water, process heat, etc.)?
RE: A thought on efficiency
Living in the relatively isolated (apparently) Houston area, I was unable to get "cheep" energy, and paid $0.18/kWh all summer. Some of my coworkers were paying $0.24/kWh. How "cheep" is it where you are?
RE: A thought on efficiency
The gas burning power plant would have to run longer to come up to temperature to put out the same heat as the furnace. If you have use for continuous heat and rotary drive power off the engine, then yes it is a great idea.
And unless the cost of electrical power is high enough, it usually ends up costing you to generate the power you sell back to the power company. Unless the fuel you use is free.
RE: A thought on efficiency
RE: A thought on efficiency
I was focusing on why, given better thermal efficiency, cogeneration was not used at the residential level, which is what I read as the main purpose of the OP. And I inadvertently threw the overused term "efficiency" back in there with a different meaning. Great posts, btw.
RE: A thought on efficiency
The Honda and Marathon solutions are what I was interested in.
Too bad they are not available yet where I live (Northwest USA).
Hydrae
RE: A thought on efficiency
imagine that I had a genset at home with the following parameters:
air cooled
engine thermal efficiency 20%
generator efficiency 80%
engine power 3.75kW
genset power output 3kW
If I run that genset for an hour, I'll generate 3kWh electricity. I'll burn about 64kBTU of fuel (for a cost of $0.78). In the wintertime (last winter) that electricity would have cost me $0.13/kWh to $0.17/kWh ($0.39 to $0.51) depending on the month. Waste heat from the genset would be about 15.75kWh or 54kBTU. If I could capture 60% of the waste heat (seems low), that'd be about 9.45kWh or 32.4kBTU into the house. My house is equipped with a pair of 66kBTU/hr 80% efficient furnaces, so I'd be looking at the equivalent heat input (to house) of running both on a 30% duty cycle. The same heat provided by my heaters would cost $0.50 for gas and (x) for electric. For that particular hour, I'd come out somewhere between $0.09 and $0.23 ahead (plus whatever (x) comes out to) if I could use the electricity or run the meter backward. If I could only get a fraction of the purchase price of electricity back, then I wouldn't likely come out ahead... then again, I wouldn't necessarily expect that combined heat/power would make much sense in Houston, TX. In Illinois or Michigan we might get a very different answer.
A 30% duty cycle is a bit much in the daytime around here, but perhaps more reasonable in the evening/night during the winter. As luck would have it, I also use more electricity in the evening than during the day.
RE: A thought on efficiency
RE: A thought on efficiency
But to do that you have to use most all the heat from the system. If you sized it right then it should accomplish what you want. But like I said unlike the furnace, the cogen will be running all the time. So you need a use for the excess heat/motive power. I haven't kept up with the cost of electrical power. But the way it works is, we pay something like .07 / KWH and if we manufacture electricity to sell back we only get the grid price of say, .01 /kwh, and that will not cover the costs to generate it.
Now if you have close neighbors that need some cut rate power you can sell to them and make it worth it.
RE: A thought on efficiency
RE: A thought on efficiency
But remember that even at all that with that theorhetically efficient machine, you still lose a lot of the exhaust heat because you can't heat it below just the north side of 300 degF due to condensation and acid corrosion problems in the exhaust system, or alternatively build it out of some prohibitively expensive materials.
All of this is theorhetical and nice banter for engineers but the reality is that it would take the lifetimes of most of my children and their children to amortize the costs of such equipment on an individual housing unit basis hence the truth of Zapster's first post notwithstanding his confustion with the terms cogeneration and combined cycle.
rmw
RE: A thought on efficiency
Regards
Pat
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RE: A thought on efficiency
I'm speculating now, but perhaps ultra low sulphur fuels might mitigate the problem. Just carbonic acid rather than sulphuric, but I don't know enough about corrosion to decide whether this makes enough difference to the metallurgy.
RE: A thought on efficiency
The lower the temp the less the corrosion once you have already got below the condensation point.
Regards
Pat
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RE: A thought on efficiency
Hydrae
RE: A thought on efficiency
RE: A thought on efficiency
RE: A thought on efficiency