Thread: Can geo-thermal be adapted for low temp differences ?

So, if the earth is a constant 50 degrees or whatever at about 10 feet below the surface, and let's say that the surface temperature reaches 90+ degrees in the summer and 10 in the winter... that's a difference of 40 degrees in temperature.

I would think that one could design a heat engine to make free energy at the times of the year when heating and cooling are consuming massive amounts of electrical power.

I'm talking about a steam-like heat engine with a closed system and heat exchangers, with a fluid that condenses/boils at either above or below 50 degrees.

Why could or wouldn't this work?

You are describing more of a primitive solar energy system than geothermal. As a heating system, you are describing a heat pump which has been used for decades. However, anyone who has ever used a heat pump knows that they don't work particularly well. That said, the best performing heat pumps extract their heat from tubes buried below the frost line.

As for using the temperature differences during the summer, your best bet is a Sterling cycle engine. Sterling cycle engines have the same theoretical efficiency as the Carnot cycle. However, the relatively low temperature of the heat source means that your engine will have very low efficiency. You are much, much better off with photovoltaic cells or solar water heaters.

From Stirling engine - Wikipedia, the free encyclopedia


"To summarize, the Stirling engine uses the temperature difference between its hot end and cold end to establish a cycle of a fixed mass of gas, heated and expanded, and cooled and compressed, thus converting thermal energy into mechanical energy. The greater the temperature difference between the hot and cold sources, the greater the thermal efficiency. The maximum theoretical efficiency is equivalent to the Carnot cycle, however the efficiency of real engines is less than this value due to friction and other losses.

Very low-power engines have been built which will run on a temperature difference of as little as 0.5 K.[49]"


Okay, so why isn't there a Stirling-Gas hybrid car. Why is the engine heat being transferred to the atmosphere via the cooling system and exhaust temp, when that engine heat could be put to work and good use ? The heat could travel from the gas engine to the Stirling and then to the cooling system.

Dumb, da-dumb dumb, Dummmmmmmmmb !

Originally Posted by MisterMe

You are much, much better off with photovoltaic cells or solar water heaters.

The more, the merry-er. Thank you for suggesting the Strirling. That is an interesting machine.

I think you're trying to deter me because of the costs associated with the materials for the heat exchangers.
I say, on the contrary, I would have to follow traditional heat exchange design for this.
Let's say, out on the farm, I would dig a hole with a post hole digger mounted on my loader tractor.
The digging is easy. There's plenty of land.
The heat exchanger would be made of flexible Pex tubing in a coil, with insulation around the leads.
For the heat exchanger above ground,
I would use a scrap radiator from a salvage / junk yard.
And then I would probably have to buy the Striling engine,
until I figure out how to make one.
I wonder if I could modify an old hydrauling cylinder ?
You know, this Fluidyne model seems pretty simple too.

Fluidyne engine - Wikipedia, the free encyclopedia

typos galore. what I meant to say was:

The more, the merrier?. Thank you for suggesting the Strirling. That is an interesting machine.

I think you're trying to deter me
because of the costs associated with the heat exchangers.
I say, on the contrary,
I would NOT have to follow traditional heat exchange design for this,
so I could use much cheaper designs that don't require skilled assembly or welding.
The heat exchanger could be made of flexible tubing in a coil,
with insulation around the first so many feet of the underground lead.
What do you think would be the cheapest heat exchanger design ?
Let's say, out on the farm,
I would dig a hole with a post hole digger mounted on my loader tractor.
The digging is easy. There's plenty of land.

For the heat exchanger above ground,
I would use a scrap radiator from a salvage / junk yard.
and find some fluid circulation pumps.
And then I would probably have to buy the Striling engine,
unless I figure out how to make one.
I wonder if I could modify an old hydraulic cylinder ?

You know, this Fluidyne model seems pretty simple too.

Fluidyne engine - Wikipedia, the free encyclopedia[/QUOTE]

Originally Posted by Jeffrey DreamKing

I think you're trying to deter me because of the costs associated with the materials for the heat exchangers.
I say, on the contrary, I would have to follow traditional heat exchange design for this.

Yup. I remember reading about them in Mother Earth News forty years ago. A quick google should bring up scads of plans.

ETA: Here's a wiki page: Geothermal heat pump - Wikipedia, the free encyclopedia

Originally Posted by grapes

ETA: Here's a wiki page: Geothermal heat pump - Wikipedia, the free encyclopedia

D*ng! it's all blacked out now. What's going on?

Here's something neat I came across.

Electricity

Morris has got some neat ideas about power generation and his heat sources.
He plans on using ionized fluid to generate power and
internalize the heat source using a fusion generator.
That would simplify things.

Yeah, that's apparently a small hand-size nuclear fusion device that's safe enough to touch, except you might burn your fingers, and it powers a magnetohydrodynamo. Nothing about geo-thermo though.

Originally Posted by Jeffrey DreamKing

I wonder if I could modify an old hydraulic cylinder ?

You know, this Fluidyne model seems pretty simple too.

Fluidyne engine - Wikipedia, the free encyclopedia

The Fluidyne is a type of Sterling.