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  1. #1
    Join Date
    Feb 2004
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    Midwest
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    Temperature down in the ground?

    I read that the temperature in the ground goes up about 30 degrees Celsius each km^-1 farther down you get. And it gets hotter than he11 after a ways.

    Here's what I can't figure out. Let's say it's summer time and the temps stay up around 100F up here on the top. But when you go down like 10' the soil temp is like 55F.

    How's that happen when it's hotter than 55 F both below and above that depth?

  2. #2
    Join Date
    Dec 2007
    Location
    Midwest
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    638
    Heat coming from two directions. Not enough from either one makes it to the 10 foot depth to raise the temperature there.

    Though the temperature of the ground does change from season to season. I control the temperature of a professional football field , they want it kept at 45 degrees in the winter at 18" depth. It takes some heat to do that, so it does change , but ten feet down would take a lot of heat to change, there just isn't enough coming from either direction to cause it to change much.

  3. #3
    Join Date
    Mar 2004
    Location
    Grottoes VA
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    5,856
    Another way to think of it........



    How many hours in a year above 55 degs and how many hours below 55 degs.


    In New Mexico the ground temp is 68 degs. In Costa Rica it is 78 degs.
    Karst means cave. So, I search for caves.

  4. #4
    Join Date
    Feb 2004
    Location
    Midwest
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    9,919
    Quote Originally Posted by mikesands View Post
    Heat coming from two directions. Not enough from either one makes it to the 10 foot depth to raise the temperature there.

    Though the temperature of the ground does change from season to season. I control the temperature of a professional football field , they want it kept at 45 degrees in the winter at 18" depth. It takes some heat to do that, so it does change , but ten feet down would take a lot of heat to change, there just isn't enough coming from either direction to cause it to change much.
    That's a good explanation. I guess the R of the ground is greater than I thought, even though it's a few thousand degrees F in way down there. But I guess it ain't like the R in a wall. That's a REALLY DEEP WALL, like a few thousand miles.

    Obviously in the summer the ground is going to be cooler in most places.

    Does anybody know at what average depths it starts to rise like in the U.S.?

  5. #5
    Join Date
    Jul 2008
    Location
    Denver, CO
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    4,207
    the deeper you go the increased pressure causes the surrounding matter (soil, rock) to get hotter due to compression.

    To answer your second questions the rate of change of temperature with depth is referred to as the geothermal gradient. The geothermal gradient varies depending on location, so there is no uniform answer. On average, the geothermal gradient is approximately 75 degrees F per mile. In volcanically active areas, the gradient can be as high as 150 degrees F per mile. In ocean trenches, the gradient may be as low as 15 degrees F per mile. Decay of naturally occurring radioactive elements may also cause localized increases in temperature in some locations.

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