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Dumb Question About Chilling Water

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gotgas
gotgas Member Posts: 78

Where we are, like most of planet Earth, the temp 4-6 ft below the ground is about 55 degrees. Why it that not being used as part of a cooling system?

For example, I am building a house in the next couple months. The foundation footers will be about 10ft below ground level, and the basement walls on top of those. While this is all excavated, why not bury a tank or large coil by the foundation that can be used as a water chiller, then circulate that water to cool air handlers for the AC system?

The idea would be to pipe water through the tank or coil underground to chill it and then return the chilled water to the air handler. This could be a mix of pipe and underground tank large enough to provide a good reservoir of cool water.

I think the initial costs would be high, but running it would be very inexpensive, just a circulator and a fan.

I have never seen or heard of this being done, which is why I think it is probably a dumb question. Try to be kind…

Edit: Am I describing geothermal?

Comments

  • dko
    dko Member Posts: 644
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    Yes

  • Intplm.
    Intplm. Member Posts: 2,084
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    You are indeed describing Geothermal. It is available but is not always considered practical in some climates.

    From your description, it might be available in your area.

    Some well drilling contractors have taken up geothermal in their businesses. Figuring so many BTU's per foot of underground exposure. It draws the heat and cool up from the ground.

    Hopefully, someone who does geothermal for a living will offer a more specific explanation.

    gotgas
  • DCContrarian
    DCContrarian Member Posts: 305
    edited July 9
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    The problem is that the earth doesn't have an infinite capacity to provide or absorb heat, once you've warmed the earth up it no longer provides useful cooling. A very rough rule of of thumb is you need 500 feet of pipe per ton of cooling — either horizontal or vertical. Once you price out the several tons that a typical house needs the idea kind of loses its shine.

    I've read about people who excavated geothermal loops in the winter and found the entire length of the pipe encased in ice.

    gotgas
  • jumper
    jumper Member Posts: 2,333
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    Tried to use reject heat from A/C to warm earth beneath parking lot for snow melting. Did not work for most winters. And most summers needed backup for heat reject.

    gotgas
  • mattmia2
    mattmia2 Member Posts: 9,962
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    You would need an enormous amount of surface area in contact with the earth to do it passively. To keep the size of the loops practical you need to use a refrigeration cycle to drive up the delta t between the loop and the earth.

    hot_rodgotgas
  • hot_rod
    hot_rod Member Posts: 22,483
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    A earth loop geo system could be considered a solar system. The energy from the sun warms the earth, and that heat energy is pumped into the building

    I visited a job near Fairbanks where 6 large solar panels pumped heat into the ground all summer to enhance the geo HP system in the winter

    The Cold Climate Housing Research Lab at U Alaska, Fairbanks now partnered with NREL did the design

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    mattmia2gotgas
  • ChrisJ
    ChrisJ Member Posts: 15,922
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    As far as just a circulator and a fan, I would disagree.

    At best you've got a dew point of 55F and that's probably unrealistic.

    If you could manage to drop your air temperature to 60F that gives a RH of 66% at 72F.

    In my opinion you'll need some good old refrigeration no matter how you look at it.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    gotgas
  • Jamie Hall
    Jamie Hall Member Posts: 23,655
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    In dry climates one can do some really interesting things with evaporative cooling — provided one has the water supply to do it. As @ChrisJ implied, you can in fact cool the air down to the incoming air dewpoint that way.

    That is the way "swamp coolers" work — and they use very little power; just a fan. But… they do use a lot of water.

    Very common in agricultural use in drier climates.

    Also why a wooded area will be cooler than the open ground nearby.

    Fun trivia: in ancient Persia, which also is exceedingly dry but which had adequate water, the same principle was used — but without fans, just natural convection in tall stacks — to keep the well-connected cool.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    gotgasdelcrossv
  • gotgas
    gotgas Member Posts: 78
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    Good point about the humidity. I had not thought about that. Where we are humidity is an issue. If there is not going to be a significant reduction in the humidity it would not work.

  • gotgas
    gotgas Member Posts: 78
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    It has always been one of my goals in life to be like the Persians, well connected and cool. So far 0 for 2.

    delcrossv
  • jumper
    jumper Member Posts: 2,333
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    Indirect evaporative cooling and reliably low wet bulb can replace mechanical A/C. An interesting variation is regenerative cooling. Fresh air is indirectly evaporatively cooled with exhaust air. At low loads inside air approaches outside dewpoint. Now if only sea water can be used then………

  • ChrisJ
    ChrisJ Member Posts: 15,922
    edited July 11
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    That would depend on the area, as Jamie said previously.

    We've had dewpoints between 76f and 80f here over the past week.

    I don't want anything like that inside if I can avoid it at all costs.

    In a dry area, that could be a really good setup though.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • jumper
    jumper Member Posts: 2,333
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    »dewpoints between 76f and 80f « pretty sticky

    PC7060
  • DCContrarian
    DCContrarian Member Posts: 305
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    There's a song by The Who called "Another Tricky Day." This morning I was singing "Another Sticky Day."

    PC7060
  • ChrisJ
    ChrisJ Member Posts: 15,922
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    The last thing I'm doing is singing if there's a dew point of 80. 😁

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • DCContrarian
    DCContrarian Member Posts: 305
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    Legit readings from my outdoor thermometer: 80F, 99% RH.