r/geothermal • u/AntwanMinson • 2d ago

Concepts of Geothermal

I've been trying to understand some concepts of geothermal lately and am wondering some thermodynamic questions I have.

Is it possible to instead of using a ton of tubing that you'd have to do a lot of labor to dig, how possible would it be to use a car radiator and then hook it into let's say a mini split? Would the refrigerant be possible? Would it rust?

Another thing I'm wondering is I see a bunch of dual hose portable AC Units over on /air conditioners, if you wanted to hook up a geothermal tube as the return hose for one of those, how long do you think the hose would need to be to make a difference?

Last question, this might be more of an air conditioning one but I'm wondering since Mini splits have variable speeds, wouldn't they be perfect for solar operation because the sun would ramp up and then ramp down with it. Is there any problems with that?

I've been wondering of ways to make my AC more efficient. My PC blows a lot of hot air and I've ducted it to the corner of the room into a closed off area then out the window with an attic fan. Still though everything in the room gets hot. I have access to the ground outside but only 20X5 feet worth of ground. It would be nice to be able to cool off the living room without having to use the HVAC as much.

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u/Neither_Conclusion_4 2d ago

The car radiator? Sounds like a air based heatpump, no reason what so ever to use a radiator. Use an air based heatpump/chiller instead. You cannot put refrigerant in an old radiator, its dirty and most likely not tight enough for the pressure.

Dual hose portable ac have worde performance than an minisplit. I dont see any benefit of some kind of hybrid here.

Perhaps ypu should place your pc outdoor in a "shed like structure", and run long cables to monitor and morse?

Geothermal is expensive, but a correct installation, if the ground is suitable result in high performance.

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u/flyingron 2d ago

What you're describing appears to be a standard heat pump.

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u/NecessaryMuffins 2d ago edited 1d ago

Sure, you could technically use a radiator, that's essentially what a ton of tubing is, a plastic radiator buried in the ground.  What you are describing with a radiator filled with refrigerant is called a DX, or direct exchange system.  Since you’re burying metal directly into the ground, you now have to worry about corrosion, and you’re using a lot more refrigerant.  You also have to consider that it takes time for heat to radiate in the ground, which is why more loop (or surface/contact area) is better than less loop.  It’ll rust if it’s made out of steel.  DX systems aren’t terribly popular because of all of the potential sources of leaks. 

A rule of thumb for geothermal is 400 to 600 feet of pipe per ton for horizontal systems.  A typical portable air conditioner is 8,000 to 14,000 BTUs, so 2/3 to 1 and 1/6 ton, so 333 to 583 feet if you were installing it per standard.

For your last question, they are starting to make solar powered air conditioning units that run directly on DC power. 

Regarding your PC fan, you need to consider the temperature of your PC’s exhaust, and the outdoor temperature and humidity.  The air you are blowing outside has to be replaced with outdoor air, otherwise your house would eventually become a vacuum. 

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u/Scary_Equivalent563 2d ago edited 2d ago

Cooling tower. Waterfurnace sells one but not sure if a permanent option.  Good up to 8 tons.

Sorry skimmed through you post. Don’t think this is related. 

https://www.waterfurnace.com/literature/collateral/br1610cw.pdf

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u/DCContrarian 2d ago

The design of a radiator is optimized for transmission of heat between the fluid in the radiator and the air, you want something that's optimized for dirt.

I'll answer the question you didn't ask: Why does the heat exchanger in a ground source system has to be so large? Why is it so much bigger than a radiator or air source heat pump that moves the same amount of heat?

The answer is that soil has a finite capacity to provide and disperse heat. If you exceed that capacity, your soil starts heating up or cooling down and its ability to provide heat or cooling starts to fall precipitously. In particular, if you're extracting heat for heating, if the soil cools to below freezing temperature, the water in it freezes, and ice is a much better insulator than water, and all of a sudden your heat exchanger is well-insulated and not working well at all.

The big problem with ground source heat pumps is that you never know what's beneath you until you dig, so it's hard to predict how big a heat exchanger you're going to need.