Posted by ghostwriter on January 8, 2006, 2:03 am
<Snipped to save space>
You have about the same approach to the idea that I have, start with a
traditional geothermal heat pump set up and try small upgrades from
there. And I certainly agree that a liquid heat exchanger moves heat
faster than a gas based one. The major issue that I see is that a low
pressure steam engine and/or a vapor turbine are machines that get more
effient the larger they are. Stirlings have the advantage of slower
movement and therefore less friction based ineffiencies (they of course
have a list of their own unique ineffiencies). That means to optimize
a small vapor turbine you would need percision bearings and perfectly
balanced bades, things that require the services of a custom machinist.
A steam engine requires a crankshaft and machined pistons and would
be difficult to time since expantion speed would be dependent on temp
difference. Addditionally a steam engine only uses the expansion side
of the cycle, whereas both the vapor turbine and the stirling use both
heating and cooling.
The vapor turbine is the best idea I think given the ineffiency of a
small steam engine(especially running on low pressure steam). But the
reason that small aircraft still use props is because microturbines are
expensive to manufacture and traditional turbines dont reach the
effiency of piston engines until they get above a certain size.
Perhaps the best system for a small scale generator would be a hybrid
stirling using a phase change material, but that would require a lot
of check valves and a computer based system to optimize timing etc. as
well as needing careful installation to prevent vapor lock or flow
abnormallities. But in exchange you would get a higher effiency and a
smaller heat exchanger. as well as getting the advantages of the
cooling side contraction. And of course a lot lower price per Kw than a
microturbine.
Ghostwriter
Posted by MadDogR75 on January 8, 2006, 5:43 am
>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
You will find that your source is not "practically unlimited".
It is practically limited by the heat conduction in the ground you are
tapping. The more you draw, the larger the surface area you must
present
and as your draw gets larger, the volume you can effectivly tap grows
smaller in relation to the area you present. Once you tap-out that
volume,
there goes your delta T.
As to OTEC, a google searce will find you a french project that was
planned somewhere in Africa but did not get funding.
Posted by MadDogR75 on January 8, 2006, 5:57 pm
> 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.
You will find that you do encounter limits.
The limiting factor will be the ability of the soil to conduct heat
to your collector. No matter how large you make it, the rate at
which you can draw energy is limited. You will find that unless
you're tapping a volcanic heat source, you are economically limited
to installations of small capacity. (The square/cube law applies and
soil conduction rates are generally low.)
The OTEC systems you mention, and certain ground-water systems
don't neccessarilly have this problem, but Geothermal, as you describe
it, does.
BTW open circuit OTEC with a solar component does look promising
for certain locations where the byproduct, (desalinated water), might
be particularly desirable.
MadDog
Posted by ghostwriter on January 8, 2006, 9:50 pm
<Snipped to save space>
You have about the same approach to the idea that I have, start with a
traditional geothermal heat pump set up and try small upgrades from
there. And I certainly agree that a liquid heat exchanger moves heat
faster than a gas based one. The major issue that I see is that a low
pressure steam engine and/or a vapor turbine are machines that get more
effient the larger they are. Stirlings have the advantage of slower
movement and therefore less friction based ineffiencies (they of course
have a list of their own unique ineffiencies). That means to optimize
a small vapor turbine you would need percision bearings and perfectly
balanced bades, things that require the services of a custom machinist.
A steam engine requires a crankshaft and machined pistons and would
be difficult to time since expantion speed would be dependent on temp
difference. Addditionally a steam engine only uses the expansion side
of the cycle, whereas both the vapor turbine and the stirling use both
heating and cooling.
The vapor turbine is the best idea I think given the ineffiency of a
small steam engine(especially running on low pressure steam). But the
reason that small aircraft still use props is because microturbines are
expensive to manufacture and traditional turbines dont reach the
effiency of piston engines until they get above a certain size.
Perhaps the best system for a small scale generator would be a hybrid
stirling using a phase change material, but that would require a lot
of check valves and a computer based system to optimize timing etc. as
well as needing careful installation to prevent vapor lock or flow
abnormallities. But in exchange you would get a higher effiency and a
smaller heat exchanger. as well as getting the advantages of the
cooling side contraction. And of course a lot lower price per Kw than a
microturbine.
Ghostwriter
Posted by Arnold Walker on January 7, 2006, 7:09 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?
Are you good at machining your own parts......Reliable Steam Engine Co. in
Tidewater,Oregan
has both several piston and one microturbine castings and plans.
Bechmann Boatshop Limited in Slocum,RI has castings,plans ,and ready made
piston.
Tiny engine has moved ....death of the previous owner to Virginia, not sure
on them.
Cole Power Models does good now ,after the death of the husband.
Located in California.She appears to have been close to his work and kept
the original employees.
This is the third genration of Coles running the business.
Leroy Mietzner has an engine he just finished. Listed on N.W. Steam Society
classified.
Preston Steam products in Kent Engine usually has both piston and microsteam
antique engines.
Microturbines were used on a lot of steam buses and lorries to spin the
generator.
British Army didn't use batteries on their radios until the early 60's so
you might find a Ricardo
steamplant(6v field radio power),as well.
Just running off memory ....might check for other names on records,if I get
a chance.
Are you near the river in that basin.....might test your idea in the water
source during the summer
months.In the Southern states , it would work for outright system, in
winter, as well......not sure
about New Hampshire.Easier to haul coils and condensers in /out of lake or
river than ground as you tune/test.
Though if you hit ground water it would be the same difference on setup
expense.
> 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
>
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>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