A thought on efficiency

[hydrae]

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

 

[Zapster]

Please share you economic calculations so that we have something to comment on. Have you generated a pro forma that details all of the variables including indirect & direct costs for the added liability? When you are done, let us know what the IRR should be for this project? Is this the best investment for your money?

 

[SomptingGuy]

Err, this is just CHP, right?

- Steve

 

[GregLocock]

Well, the first time I saw it was in the early 70s on Tomorrow's World. Fiat engine (1500cc?) running on gaseous gas as opposed to the other stuff. Supplies electrickery for a hotel via an AC generator, and hot water.

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

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ivymike]

http://www.polarpowerinc.com/products/generators/cogenset.htm

 

[ivymike]

http://www.cumminspower.com/na/solutions/cogeneration/

http://www.marathonengine.com/cogeneration.html

http://www.energytomorrow.org/Cogeneration.aspx

http://www.theoildrum.com/node/3723

http://www.cogeneration.org/

 

[Zapster]

Cogeneration has been around a very long time, economics is the driver as to whether it is a reasonable approach. The economics must be viewed on a case by case basis based on the environment. There is an economy of scale when it comes to first-cost, maintenance, design, liabilities, fuel costs, etc. If the economics show it is profitable, you do it, otherwise you don't unless you are a government agency or a hobbyist.

 

[Zapster]

Here is an overview of what is already available:

http://www.ecbcs.org/docs/Annex_42_Review_Residential_Cogen_Technologies.pdf

 

[JSteve2]

Well, you're not going to beat grid power for efficiency as that runs off a dedicated generator and fuel of choice. You're not going to beat a burner for heating efficiency, as there are no moving parts or expensive replacement parts. So, unless you need the portability and grid independence, there is no need for such a system.

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.

 

[ivymike]

not going to beat grid power for efficiency

um, cogeneration?

 

[JSteve2]

ivymike:
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.

 

[Zapster]

I thought that most new/upgraded base line power plants in the USA were cogeneration and efficient. At least they are in my area (no coal is used here, only natural gas fired turbines with HRSGs). I also thought that in areas where coal is used, even these plants use cogeneration with the recovered low grade heat being used for commercial/industrial applications when it is economical. In contrast, peaking generation sets in my area are not cogeneration. I can think of two power plants that have pushed their efficiency even further with trigeneration where they use the low grade heat for heating/tempering of water for commercial/industrial usage. When you consider the economy of scale and the fact that the large electric utility companies can buy natural gas cheaper than I can, residential cogeneration is not even worth considering in these areas.

For some isolated areas where cheep energy is not available, residential cogeneration might make sense.

 

[drwebb]

Honda is already testing the waters in the NE US:

http://www.hondapowerequipment.com/products/homeenergy/freewatt.aspx

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?

 

[ivymike]

Jsteve - oh, "efficiency" in kwh/$. I thought you were talking about efficiency (of energy conversion), as in the OP.

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.

 

[Zapster]

ivymike, as I stated "thought new/upgraded base" not the entire base load. Are you stating that only 8% of new natural gas power plants are cogen? Or that only 8% new/upgraded base sets are cogen? Or are you talking about 8% of the total generating capacity of the united states both base and peaking sets have cogen capabilities. Please define what you are saying because I have no idea what your 8% represents.

 

[ivymike]

Reading misc. articles on the internet, one might get the idea that cogeneration is commonly used at relatively small facilities (not utilities) to reduce the money they spend on electricity.

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

http://www.epa.gov/chp/markets/municipalities_fs.html

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.)?

 

[ivymike]

... and by the way, when you say "natural gas fired turbines with HRSGs," I would've assumed that those are used for bottoming cycles in combined cycle power plants (to generate more electricity), not for "cogeneration" where the heat itself is a desired product. Do you know which is the case?

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?

 

[dicer]

Simply put, the gas heater is only on when the thermostat tells it to put out heat.
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.

 

[drwebb]

"The average efficiency of fossil-fueled power plants in the U.S. is 33% . . ." A surprising figure to me, but very much in line with Honda's figures. Now what if their system were used to heat a home and charge a plug-in electric's batteries overnight?

 

[JSteve2]

ivymike:
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.