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geothermal storage?

DrDoggy

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Joined
Sep 21, 2022
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Hi all,
Thanks for having me!
I just started reading about seasonal geothermal storage. I read alot about how efficent it all is, but maybe not since there is confusion about storage and a true system,

My first question is for example if i put a tube in the ground then fill it with hot water it will dump the heat in to the ground. as I dump the heat the surrounding ground warms up. but then winter comes and i then dump cold water in the ground forcing the water to extract and retrieve the heat which i can use, but as the heat is sitting in the ground it is radiating outward away from my pipe, so the only heat i can collect is the remaining heat that has not spread out.

If this is the case doesnt that mean that the efficency can only be 50% or less?
Am I confuseing the 90% efficency i read about with other systems?

Thanks!
 
Hi all,
Thanks for having me!
I just started reading about seasonal geothermal storage. I read alot about how efficent it all is, but maybe not since there is confusion about storage and a true system,

My first question is for example if i put a tube in the ground then fill it with hot water it will dump the heat in to the ground. as I dump the heat the surrounding ground warms up. but then winter comes and i then dump cold water in the ground forcing the water to extract and retrieve the heat which i can use, but as the heat is sitting in the ground it is radiating outward away from my pipe, so the only heat i can collect is the remaining heat that has not spread out.

If this is the case doesnt that mean that the efficency can only be 50% or less?
Am I confuseing the 90% efficency i read about with other systems?

Thanks!
I don't think one could effectively use the earth as long term heat storage without some sort of insulation. I did see a design some years ago where a big office building was constructed with a large insulated mass of wet sand in an underground chamber under the building. An antifreeze solution was circulated to an outside heat exchanger during the winter to freeze the mass of wet sand. Then in the summer they reversed the cycle to put building heat into the cold sand mass, removing heat from the building.

Recently I saw a design where an insulated room of sand was heated by solar to bank heat for the winter. The room was inside the building and well insulated. So heat loss from the heated mass would be lost to the inside of the building. Since heating the building was one of the design goals, this was okay. By the way, the sand was hot enough to make steam from, so they could run a boiler and generator from it.
 

this is just another example i am looking at but they all seem similar, just like the ones that burry horizontal loops. but are they all insulated in such fashion mentioned?
 
I see one side of the cycle still has a heat pump in the design. I have had a geothermal heat pump for 39+ years. It is hard to imagine in a house size scale that you could ever alter an underground space's heat enough to be very useful. A good heatpump can take great advantage of the heat or heat sink of the ground. I also dump my heat from my air conditioning cycle into a preheat water heater, to my summer water heating energy is very low.

I have some potential solar power that is not used. I have a crawl space and I have considered putting an insulated mass in the crawl space and heating that with solar. Lots of ideas.
 
I don't think the idea is to store energy in the ground as much as it is to take advantage of the relatively stable in-ground temperatures. If the temperature at some depth is, say, 20 degrees warmer than the atmosphere, you could use a heat pump to extract that energy and heat your home. And the opposite is true in the summer.
 
I don't think the idea is to store energy in the ground as much as it is to take advantage of the relatively stable in-ground temperatures. If the temperature at some depth is, say, 20 degrees warmer than the atmosphere, you could use a heat pump to extract that energy and heat your home. And the opposite is true in the summer.
Exactly. Changing the ground temperature is undesirable because you gradually lose your temperature differential as the heating or cooling season progresses. They size the buried loops in part based on how effectively the soil/groundwater moves heat towards or away from the loops. If the local ground tends to trap heat they have to make the loops longer. That adds cost, so you want ground that's good at moving heat away instead of storing it.
 
I recently visited a food plant that requires hot water for their process (85*C). Besides introducing a heat pump soon, they will do thermal storage in one single tank. I do not think insulating is very complicated; nowadays there are many materials (even waste materials) that can offer you a decent thermal insulation; but no matter how good it is, it is only for temporary storage. In that food plant they can store the hot water within the operating range for no more than 8 hours. If you use insulation like in the refrigeration equipment (eg. Liquid nitrogen) you can probably even double that time but at a $$$$$ cost.

When you do that in pipes underground, you are just using the ground as a free insulator and taking advantage of the ground sun heat retention (winter) and ground insulation to keep your water fresh (summer).

Such effects here mentioned are strongly influenced by daily weather conditions and also follow a seasonal trend; but as storage I would not expect periods longer than 24h; in fact the whole temperature cycle of geothermal I guess happens in 24h.

The easiest example of geothermal (even though there is no specific installation build in my building) is that in summer at 35*C the tap water comes fresh at 20*C and in winter, at 0*C the water still comes slightly warmer at 15*C. The pipes underground are kind of doing geothermal storage.
 
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