Posted by bsr3997 on January 1, 2006, 5:19 pm
Hi all,
I've been kicking some ideas around about using geothermal energy for
heating and power production. I live in New Hampshire in the
northeastern USA. It looks like the ground temp is about 50 F degrees
around here.
http://www.smu.edu/geothermal/2004NAMap/Geothermal_MapNA_7x10in.gif
Air temps usually range from -25 to +95 with the lowest I have seen at
-40. My particular location is in a river basin with sandy soil.
There is rock not too far down and I suspect there is ground water near
the surface.
I currently heat with oil, having a baseboard hot water system. The
furnace is rated for 106,000 BTU/H. When it's -20 deg the furnace runs
more than half the time.
My first question would be, what kind/size of ground loop(s) would I
need to draw that amount of heat out of the ground?
The second part of my plan is to use the same ground heat to power the
heat pump. A text book I have on thermodynamics has a nice write-up on
a OTEC project that was actually built back in the 1970's. I forget
the exact output, but it was small by industrial standards. It covered
a barge and flowed hundreds of gallons per minute, so it was still much
larger than anything I have in mind. My main interest in it is that it
showed that it was practical to extract energy from a 40 F deg
temperture difference.
http://www.seasolarpower.com/images/slides/Slide5.GIF
I would be looking to start small with this, suplimenting my current
heating system as opposed to replacing it. If things work out I can
expand it later.
The OTEC project I studied used amonia as a working fluid. Where this
will be built in the basement of my home I thought freon would be
safer. The ozone friendly forms they sell now are not as efficient as
amonia, but they are a lot easier to live with.
The OTEC project used a turbine to extract energy from the working
fluid. I know of no micro turbines in the 1 to 2 KW range, so I will
probably end up with some sort of piston driven steam engine. Anybody
got a good place to start looking?
I was thinking a ground loop similar to the one for the heat pump would
serve as the boiler, while an above ground loop would provide a heat
sink. Another possibility for a sink would be a shallow ground loop in
frozen ground. It could assure there would be at least a 20 degree
difference even when the air temp was above freezing. I get a strange
satisfaction from the idea of using frozen ground to generate power :)
Another possibility would be to use a small burner to heat a boiler
coil in the cellar, running the "steam" through the steam
engine/generator, and then a condensor. All the waste heat would go to
heating the house, while the power produced could run a heat pump.
The eventual goal is to have a geothermal powered generator powering a
heat pump. One of the best things about it would be that the colder it
got, the better it would work. But, it has to be made at a reasonable
cost.
Anybody know of others that have tried this? Any links to small steam
(freon) powered generators? How about a steam powered pump, skiping
the electric stage and going straight to a heat pump?
Least anyone think we are pulling ourselves up by our bootstraps here,
think of it as a water wheel turning a pump to pump a small amount of
water to a higher level by letting more water flow down over the wheel.
Enough food for thought. Comments?
Bruce S Richmond
Posted by ghostwriter on January 3, 2006, 3:32 pm
Its an idea that I have had in the past. I imagine that a lot of
others here have had it as well.
The problem is not that the system wouldnt work, it is that it would
be expensive to set up a large system and take considerable fine tuning
in order for it to make any money at all. And that means you are at
serious risk of losing your ass on a project like this.
Assuming a 15C temp difference for 6 months out of the year (greater in
summer, lower in winter), your max power becomes 3% of your available
heat. Now since your available heat is essential unlimited that 3% is
not a large problem. The problem becomes when you build the heat
engine to get to that energy, a freon heat pump doesnt work well under
that small of a heat difference. Freon is used because it sucks or
dumps a lot of heat when it is compressed or expanded whereas in a heat
engine you what a molecule that expands or contracts quickly when
heated or cooled. I have never heard of a heat pump used as a generator
under low temps with a phase change coolant. I have read up a little on
the otec project, construction of a vapor turbine strikes me as
difficult and expensive. Have you been able to locate any drawings, or
specs?
A stirling engine sounds more feasible to me, a relativly simple
system but one that you would have to build yourself. The best working
fluid for a stirling is hydrogen, since it contracts and expands faster
than any other gas. Hydrgoen is so small a molecule that it can
penetrate metals and make them brittle and it is impossible to contain
absolutely, industrial users simply attach a pressure bottle to make
sure enough stays in the engine. The preformance of a stirling
improves as the working fluid is pressurized, which makes the leaking
and embrittling worse. Compressed air can be used instead of hydrogen,
and simply compressed to a higher level but that means sacrificing some
performance.
The laws of thermodynamics say that any heat engine (be it a stirling
or a vapor turbine) can only get as much work out as the temp
difference between the source and the sink divided by the temp in
Kelvin of the source. That means a 15K difference has a max effiency
of about 5%. Homebrew performance would be about a quater of the ideal
say 1.25% (seapower claims 3.25% but they also claim a 22C difference).
That means that both your heat exchangers would have to be sized to
move 80times more watts of heat than the watts of power you wanted out
of your motor. Given the poor heat transfer of dirt as compared to
water that is one large heat exchanger on at least one side of the
system (you can use a well as a open source heat exchanger for the
ground temp). You could in theroy use a large pond as a open source
for the air temp but it would have to be large and shallow since water
has a large specific heat.
This is the reason that they want to use the oceans of the equator as
both the source and the sink. Effectively then both heat exchangers are
infinitly bigger than any power load their generators could need.
Ghostwriter
Posted by Arnold Walker on January 3, 2006, 5:49 pm
You need to google (or whatever your search engine is ) kalina. It's the
modern day development of that method.
It is used ,not only on geothermal ,but biomass and cogen generation power
plants as well.
On some of your concern about freon being safer than ammonia.
Did you not notice, that a cup of freon,ammonia,or water(at operating
pressure) will remove all air in a 100 cu.ft.room
in microseconds with a major leak or broke line.
Or that ammonia will give a warning with smell ,on a leak long before it
becomes a problem.
Or that halon was freon 12.....gives an idea of what freon will do to your
lungs.
Safety measures are more important....like ventilation,etc.
Just a few thoughts from a steamer.......that has worked with kalina cycle.
All three under the right conditions can basicly rip your lungs out and
stomp on them with spike shoes.
If you have any doubts about dangers of water.....consider that pools are
one of the leading causes of accidental death in kids.
Add heat and it is even meaner....
You don't want to be near anyone who breaks safety rules while using any of
these items.
The fact all three exist in a home already.....says sombody is tring to live
by the safety rules.
At least ,in the homes with living occupants....
Kalina has many books on it and operating powerplants.......You can expect
60-80% effecency on cogen and geysters like San Francisco and Iceland
Dr. Alexander Kalina first publihed his idea in 1983.The fact large plants
are already running ,speaks for the merits of the idea.
> Its an idea that I have had in the past. I imagine that a lot of
> others here have had it as well.
> The problem is not that the system wouldnt work, it is that it would
> be expensive to set up a large system and take considerable fine tuning
> in order for it to make any money at all. And that means you are at
> serious risk of losing your ass on a project like this.
> Assuming a 15C temp difference for 6 months out of the year (greater in
> summer, lower in winter), your max power becomes 3% of your available
> heat. Now since your available heat is essential unlimited that 3% is
> not a large problem. The problem becomes when you build the heat
> engine to get to that energy, a freon heat pump doesnt work well under
> that small of a heat difference. Freon is used because it sucks or
> dumps a lot of heat when it is compressed or expanded whereas in a heat
> engine you what a molecule that expands or contracts quickly when
> heated or cooled. I have never heard of a heat pump used as a generator
> under low temps with a phase change coolant. I have read up a little on
> the otec project, construction of a vapor turbine strikes me as
> difficult and expensive. Have you been able to locate any drawings, or
> specs?
> A stirling engine sounds more feasible to me, a relativly simple
> system but one that you would have to build yourself. The best working
> fluid for a stirling is hydrogen, since it contracts and expands faster
> than any other gas. Hydrgoen is so small a molecule that it can
> penetrate metals and make them brittle and it is impossible to contain
> absolutely, industrial users simply attach a pressure bottle to make
> sure enough stays in the engine. The preformance of a stirling
> improves as the working fluid is pressurized, which makes the leaking
> and embrittling worse. Compressed air can be used instead of hydrogen,
> and simply compressed to a higher level but that means sacrificing some
> performance.
> The laws of thermodynamics say that any heat engine (be it a stirling
> or a vapor turbine) can only get as much work out as the temp
> difference between the source and the sink divided by the temp in
> Kelvin of the source. That means a 15K difference has a max effiency
> of about 5%. Homebrew performance would be about a quater of the ideal
> say 1.25% (seapower claims 3.25% but they also claim a 22C difference).
> That means that both your heat exchangers would have to be sized to
> move 80times more watts of heat than the watts of power you wanted out
> of your motor. Given the poor heat transfer of dirt as compared to
> water that is one large heat exchanger on at least one side of the
> system (you can use a well as a open source heat exchanger for the
> ground temp). You could in theroy use a large pond as a open source
> for the air temp but it would have to be large and shallow since water
> has a large specific heat.
> This is the reason that they want to use the oceans of the equator as
> both the source and the sink. Effectively then both heat exchangers are
> infinitly bigger than any power load their generators could need.
> Ghostwriter
>
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Posted by ghostwriter on January 4, 2006, 6:17 am
Thanks for the suggestion but the point I had made in my orginal post
was that phase change coolants were not effient at low temp difference,
Everything I have read on Kalina says dont attempt it if the temp
difference is lower than 100F. That low grade geothermal suggested in
the first post was 30-40F temp difference. Compressed air in a
stirling also eliminates the safety concerns of decompression of phase
change coolants.
Do you have and links for the use of kalina for low grade heat
applications?
Ghostwriter
Posted by Bruce Richmond on January 7, 2006, 2:08 am
ghostwriter wrote:
> Its an idea that I have had in the past. I imagine that a lot of
> others here have had it as well.
> The problem is not that the system wouldnt work, it is that it would
> be expensive to set up a large system and take considerable fine tuning
> in order for it to make any money at all. And that means you are at
> serious risk of losing your ass on a project like this.
Which is why I intend to start small to test the concept.
> Assuming a 15C temp difference for 6 months out of the year (greater in
> summer, lower in winter), your max power becomes 3% of your available
> heat. Now since your available heat is essential unlimited that 3% is
> not a large problem. The problem becomes when you build the heat
> engine to get to that energy, a freon heat pump doesnt work well under
> that small of a heat difference. Freon is used because it sucks or
> dumps a lot of heat when it is compressed or expanded whereas in a heat
> engine you what a molecule that expands or contracts quickly when
> heated or cooled. I have never heard of a heat pump used as a generator
> under low temps with a phase change coolant. I have read up a little on
> the otec project, construction of a vapor turbine strikes me as
> difficult and expensive. Have you been able to locate any drawings, or
> specs?
Actually the temp difference will be greater in the winter, near 40C at
times. That is part of what got me on this, the power available will
be greater when most needed.
I may hve worded things poorly in my previous post. What I ment was
for a steam engine to power a generator, or a heat pump directly.
I found the text book. The project was called the Mini-OTEC
demonstration plant and was built by Lockheed. It used ammonia as a
working fluid with a temp difference of 37F degrees. 80 deg water
entered the evaporator and left at 75 deg. 43 deg. water entered the
condenser and left at 50 degrees. Both heat exchangers flowed 2700 GPM
of water. The parts of the system where the ammonia was liquid it
flowed at a rate of 58.5 GPM. The turbine-generator had an inlet
pressure of 130 psia and an oulet pressure of 92 psia, producing 50 KW.
It also mentioned that the US DOE was investigating the use of
thermoelectric OTEC. Don't know if that ever went anywhere.
> A stirling engine sounds more feasible to me, a relativly simple
> system but one that you would have to build yourself. The best working
> fluid for a stirling is hydrogen, since it contracts and expands faster
> than any other gas. Hydrgoen is so small a molecule that it can
> penetrate metals and make them brittle and it is impossible to contain
> absolutely, industrial users simply attach a pressure bottle to make
> sure enough stays in the engine. The preformance of a stirling
> improves as the working fluid is pressurized, which makes the leaking
> and embrittling worse. Compressed air can be used instead of hydrogen,
> and simply compressed to a higher level but that means sacrificing some
> performance.
The text had this to say about the Stirling cycle, "The Stirling cycle
has for some time been only of historical interest, since it has not
been used as a prototype for practical power-producing systems.
Recently interest has been revived and engines based on the Stirling
cycle have been built and successfully operated. This development has
been due to the possibility of using these engines for power production
in space."
I found this site that explains the cycle:
http://www.whispergen.com/main/stirlingcycle/
Seems like the heat exchangers would need to be bigger when working
with gas as opposed to liquid. Will be studying it more.
> The laws of thermodynamics say that any heat engine (be it a stirling
> or a vapor turbine) can only get as much work out as the temp
> difference between the source and the sink divided by the temp in
> Kelvin of the source. That means a 15K difference has a max effiency
> of about 5%. Homebrew performance would be about a quater of the ideal
> say 1.25% (seapower claims 3.25% but they also claim a 22C difference).
> That means that both your heat exchangers would have to be sized to
> move 80times more watts of heat than the watts of power you wanted out
> of your motor. Given the poor heat transfer of dirt as compared to
> water that is one large heat exchanger on at least one side of the
> system (you can use a well as a open source heat exchanger for the
> ground temp). You could in theroy use a large pond as a open source
> for the air temp but it would have to be large and shallow since water
> has a large specific heat.
> This is the reason that they want to use the oceans of the equator as
> both the source and the sink. Effectively then both heat exchangers are
> infinitly bigger than any power load their generators could need.
> Ghostwriter
I'm thinking of starting by just driving a couple of pipes into the
ground to see how much heat I can draw out. With luck they may hit
ground water that will help the heat transfer. At least it will give
me an idea of what I have to work with.
Bruce Richmond
XML site map
> others here have had it as well.
> The problem is not that the system wouldnt work, it is that it would
> be expensive to set up a large system and take considerable fine tuning
> in order for it to make any money at all. And that means you are at
> serious risk of losing your ass on a project like this.
> Assuming a 15C temp difference for 6 months out of the year (greater in
> summer, lower in winter), your max power becomes 3% of your available
> heat. Now since your available heat is essential unlimited that 3% is
> not a large problem. The problem becomes when you build the heat
> engine to get to that energy, a freon heat pump doesnt work well under
> that small of a heat difference. Freon is used because it sucks or
> dumps a lot of heat when it is compressed or expanded whereas in a heat
> engine you what a molecule that expands or contracts quickly when
> heated or cooled. I have never heard of a heat pump used as a generator
> under low temps with a phase change coolant. I have read up a little on
> the otec project, construction of a vapor turbine strikes me as
> difficult and expensive. Have you been able to locate any drawings, or
> specs?
> A stirling engine sounds more feasible to me, a relativly simple
> system but one that you would have to build yourself. The best working
> fluid for a stirling is hydrogen, since it contracts and expands faster
> than any other gas. Hydrgoen is so small a molecule that it can
> penetrate metals and make them brittle and it is impossible to contain
> absolutely, industrial users simply attach a pressure bottle to make
> sure enough stays in the engine. The preformance of a stirling
> improves as the working fluid is pressurized, which makes the leaking
> and embrittling worse. Compressed air can be used instead of hydrogen,
> and simply compressed to a higher level but that means sacrificing some
> performance.
> The laws of thermodynamics say that any heat engine (be it a stirling
> or a vapor turbine) can only get as much work out as the temp
> difference between the source and the sink divided by the temp in
> Kelvin of the source. That means a 15K difference has a max effiency
> of about 5%. Homebrew performance would be about a quater of the ideal
> say 1.25% (seapower claims 3.25% but they also claim a 22C difference).
> That means that both your heat exchangers would have to be sized to
> move 80times more watts of heat than the watts of power you wanted out
> of your motor. Given the poor heat transfer of dirt as compared to
> water that is one large heat exchanger on at least one side of the
> system (you can use a well as a open source heat exchanger for the
> ground temp). You could in theroy use a large pond as a open source
> for the air temp but it would have to be large and shallow since water
> has a large specific heat.
> This is the reason that they want to use the oceans of the equator as
> both the source and the sink. Effectively then both heat exchangers are
> infinitly bigger than any power load their generators could need.
> Ghostwriter
>