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Old 23rd April 2010, 11:07   #1
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Default Geo Thermal Heat Exchange

For years now I've been toying with the idea of making a heat exchange between ambient air and the cooler layers of soil about 15-20 feet under. Last night I gooled casually to see if someone has thought of the same thing and was astounded to discover a considerable body of knowledge and experiments in the field. How did I come upon this in such detail? Mind boggling

One explanation I can think of is while our brains and resultant thought structures are unique/individual the human mind quite possibly is a single entity common to Mankind. How else did I discover the whole science of geo thermal heat exchange completely on my own with no exposure ever in media or in conversation with anyone. Till last night I had no clue this whole process was ever in practice anywhere!

The principle is very simple.

The temperature of soil about 10-15 feet below the surface is about the same as the average temperatures you encounter above across the year. So if you average out the winter and summer months overall the soil is always cooler in summer and warmer in winter as compared to ambient air.

Now if you build a heat exchange that funnels ambient air in a room, deep into a coil/tubes laid out inside the earth it will cool the air. This works off the principle that heat moves from hot to cold surfaces

The second element that has always fascinated me is the way a simple terracotta surai or water jug cools water to almost 20 degrees lower than ambient temperatures. Evaporation is an amazing way to cool things.

Both processes above require low energy inputs. It would be fun to build something based on both these principles. Infact one could build a air cooler based on terracotta tubes that hold water, cooling an inner tubing that carriers air

What do you guys think?

Last edited by DKG : 23rd April 2010 at 11:10.
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Old 23rd April 2010, 13:14   #2
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DKG:
The second element that has always fascinated me is the way a simple terracotta surai or water jug cools water to almost 20 degrees lower than ambient temperatures. Evaporation is an amazing way to cool things.

Coolers work on the same principle, don't they?

Another simple principle to achieve a significant level of comfort is of blocking heat exchange by keeping doors/windows closed during night in winter and during day in summer. Although we do it in winters, in summer, I have found it hard to explain it to my family that they should not let hot air from outside by closing the doors and also avoid radiant heat/direct sun by closing the curtains during the day. I have myself experimented greater comfort by following this when I am at home. The argument they have is there should be ventilation for the house to remain cooler in summer but they do not understand that it is the warmer air that is getting in the house.

Last edited by alto99 : 23rd April 2010 at 13:15.
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Old 23rd April 2010, 13:33   #3
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Originally Posted by alto99 View Post
Coolers work on the same principle, don't they?
Yes you are right.

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Another simple principle to achieve a significant level of comfort is of blocking heat exchange by keeping doors/windows closed during night in winter and during day in summer
Very true. Infact the older houses with lime walls were totally cool throughout the day when you kept doors and windows closed and curtains drawn.

These days the cement walls and roof also serve as radiators of heat. Its all so energy inefficient.

Another very interesting architectural device is the wind tower used in Arabia. Its amazing how it keeps the room below cool. They also have versions which work off the principle of evaporation in a channel underground letting in cool air.

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Old 23rd April 2010, 14:13   #4
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i think Lotus temple is cooled naturally in someway on similar principles?
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Old 23rd April 2010, 14:16   #5
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Originally Posted by DKG View Post
The temperature of soil about 10-15 feet below the surface is about the same as the average temperatures you encounter above across the year. So if you average out the winter and summer months overall the soil is always cooler in summer and warmer in winter as compared to ambient air.

Now if you build a heat exchange that funnels ambient air in a room, deep into a coil/tubes laid out inside the earth it will cool the air. This works off the principle that heat moves from hot to cold surfaces
I hope it doesn't causes any imbalance to the nature to spun off other disasters.
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Old 23rd April 2010, 14:21   #6
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I hope it doesn't causes any imbalance to the nature to spun off other disasters.
If you dig and install pipes just ten feet underground I don't see how that can cause any imbalance. For borewells you are digging as much as 1000 feet !!!
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Old 23rd April 2010, 14:24   #7
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Originally Posted by DKG View Post
If you dig and install pipes just ten feet underground I don't see how that can cause any imbalance. For borewells you are digging as much as 1000 feet !!!
Rigs upto 300 feet at my home = no big difference
Rigs upto 300 feet in my locality = something noticed
Rigs upto 300 feet in my entire city = water table imbalance

Perfect example - Sea water seeped into Chennai

Hope you got what I meant.

Last edited by aargee : 23rd April 2010 at 14:25.
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Old 23rd April 2010, 14:46   #8
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DKG, I am quite aware of Geo Thermal Cooling for a decade now. I even wanted to implement it in my office in Manipal. However, i couldn't find any GTC vendor in India to make it a reality for me.

I recently mentioned it in another thread: https://www.team-bhp.com/forum/shift...ml#post1832538
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Old 23rd April 2010, 15:04   #9
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The idea is interesting - injecting heat into mother earth!

Assume we managed to place the radiator grill with lots of small tubes to increase the exchange of heat underneath the soil. After hotter air flows through them for a while, the surrounding soil gets heated up. Since this is not going to spread that quickly through the soil, the cooling will become inefficient after some continuous usage.

How this is taken care in GTC systems?

(Just my thought)

Found this interesting diagram in the net

Geo Thermal Heat Exchange-geothermalbuilding.jpg

Last edited by clevermax : 23rd April 2010 at 15:11.
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Old 23rd April 2010, 15:34   #10
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A far more efficient system is where the pipes are laid under water in a large man made pool or natural lake. All open water bodies continuously exchange heat via evaporation keeping the water cool.
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Old 23rd April 2010, 15:38   #11
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Quote:
Originally Posted by Samurai View Post
DKG, I am quite aware of Geo Thermal Cooling for a decade now.
Considering I had never heard of it, or read about it, or met someone who knew something about it, I was puzzled as to how I figured out a system which happens to be identical to what is widely accepted as the way to implement GTC. Quite obviously many people, including yourself knew about this.

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Since this is not going to spread that quickly through the soil, the cooling will become inefficient after some continuous usage.

How this is taken care in GTC systems?
A red hot iron will cool within minutes when you set it in some soil. The soil in turn will cool in another few minutes given the larger volume of soil at cooler temps. So I don't think the degree to which you exchange heat will overwhelm the degree to which the soil will cool the pipes

If you couple this with a system that further cools due to evaporation I feel you get a reasonably good air conditioner (theoretically speaking)

Ofcourse I would need to build a working model and test it to say how effective this will be

Quote:
Originally Posted by aargee View Post
Rigs upto 300 feet at my home = no big difference
Rigs upto 300 feet in my locality = something noticed
Rigs upto 300 feet in my entire city = water table imbalance

Perfect example - Sea water seeped into Chennai

Hope you got what I meant.
So what kind of disturbance to the soil do you reckon pipes buried at 10 feet would bring about?
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Old 23rd April 2010, 15:47   #12
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Quote:
Originally Posted by Samurai View Post
A far more efficient system is where the pipes are laid under water in a large man made pool or natural lake. All open water bodies continuously exchange heat via evaporation keeping the water cool.
Don't you think the entire water body will heat up too as it remains exposed to sunlight?

The way to really optimise this is the water should be in a underground channel not exposed to sunlight. When hot dry air is routed over it the water starts evaporating lowering the surface temp. There is no sunlight to further heat the water, and in a short while the water temp starts dropping. Lets say the ambient temp is 40 deg celcious. I reckon the water can drop to 20 deg by this process. Just to illustrate what I mean leave the terracotta pot out in the sun. It won't cool the water as much despite the evaporation as the sun is heating the clay directly too which in turn heats the water. But when you leave the pot in shade the ambient dry air enables evaporation and since there is no other direct heating element to the pot's clay the inner temp starts dropping
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Old 23rd April 2010, 15:48   #13
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Guys, Geo Thermal Cooling has been around for decades and is under use in many developed countries. It works both as a heater and cooler since it maintains the same temperature throughout the year.

The real issue is why it is not available in a power-starved country like ours. BTW, there are many GTC companies and GTC consultants in India. Last time we contacted a GTC consultant in Chennai, he claimed there are no GTC installations in India. I was tempted to ask how he makes a living...
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Old 23rd April 2010, 15:59   #14
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So what kind of disturbance to the soil do you reckon pipes buried at 10 feet would bring about?
Well DKG, I'm no expert here or even have thought about this in my wildest dreams. My only strong faith being that, never disturb nature, 'cause you don't know the repurcation as no one has understood the nature. Basically trying to follow Newton's first law.
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Old 23rd April 2010, 16:43   #15
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Some very interesting examples of heat exchangers. The former is the classic wind tower that exists for thousands of years across the middle east. It seems to work on both principles of geo thermal exchange and cooling through evaporation.

The later I have never seen in application but seems to be the ideal solution for city homes with access to a roof.

Geo Thermal Heat Exchange-badgir.jpg

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Last edited by DKG : 23rd April 2010 at 16:45.
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