Asuuming Surface temp is 100 F, If I dig a hole 200 feet deep what is the temp at the bottom?

Question

landmass is lower appalachian, so no geothermic activity to offset the temp. I actually googled this for a while then decided to post here.
Any pointers to temp variation by depth in the earth would be appriciated.
Assume hole is a 3 foot shaft if that helps.

So it looks like my plan for cheap air conditioning by digging a 200 foot deep hole and running two pipes connected by a U down the hole and blowing room temp air in and expecting nice cool air out aint gonna work. Good thing I asked before I started digging.

Answer 1

At that depth the temperature is likely to be close to the annual average temperature. Your idea is excellent and is commonly applied commercially in the form of geoexchange pumps.

One reason this works, besides the fact that shallow ground is going to be near annual average temperature, is that there is an observed delay in the change of ground temperature at some shallow depth that will be about 6 months out of phase with the surface temperature. So in the summer when you need it most, there will be a cooler zone in the ground beneath you that is still affected by last winter's cooling.

The SMU Geothermal Lab has a lot of data relative to geothermal gradient. However, geothermal gradient is the 'rate of change' in temperature and not the actual temperature data, so I went through their spreadsheet data and tried to find a well temperature that would be relevant to you. Few wells have temperature readings taken at such a shallow depth as 60 meters. Here is their site, which you may find interesting:
http://www.smu.edu/geothermal/

What you are really interested in is called a geothermal heat pump. Here is a page with links to lots of information on geothermal heat pumps:
http://www.smu.edu/geothermal/GPW_TX/GPW_TX_HeatPumps.htm

Take a look at some of this information:
http://www.geoexchange.org/publications/factsheets.htm
Geothermal heat pumps have been found to be one of the most efficient methods for heating and cooling buildings, with an average of 36% more efficiency for heating and 43% more efficiency in cooling that gas heat pumps. There are over a million installations of geoexchange pumps in the US at present. Here is a diagram that shows how it works for cooling:
http://www.geoexchange.org/images/Home%20GX%20smmr.jpg

Here is another good writeup by an engineer on geoexchange:
http://www.greenbuilder.com/sourcebook/groundsource/

Here is the EPA's site on geoexchange:
http://www.epa.gov/globalwarming/greenhouse/greenhouse9/comfort.html

Answer 2

The temperature at the bottom shouldn't be a ton lower than that at the surface, at least as far as the air temperature is concerned. Because the hole is being dug and filled with surface air, and not a closed system, nor getting air from any other source, the air will only be cooled by the material surrounding the hole. The temperature of that material is going to vary by depth, warmer closer to the surface (much warmer if we're talking sunlight warmth), cooler towards the bottom, but because the air exchange in the hole is likely to be decently constant if there are things moving up and down in the hole, even that will slowly even out. There are way too many variables to give an exact answer, as I have no idea what an average ground temperature is like in lower appalachia, but remember that you're not talking about the temperature at the bottom of a sealed system or in a cave where there will be minimal air exchange. Hope that helps some !!

Answer 3

Depending on the location, below 3 to 4 feet, the temperature of the earth is approximately 50 to 55 degrees F. At a depth of 200 feet, there should be no measurable difference and the temperature should be 50 to 55 degrees F. This will vary greatly if there is geothermal sources nearby.

Answer 4

Tempreture closer to the earth's core will increase however at a depth of 200 ft there will be no difference in fact it will probably be a bit cooler because of the moisture that is in the surrounding soil and the shade from the sun that is produced from being under ground.

Answer 5

As you dig inside the Earth the temperature would only increase because at Earth's centre lies molten lava ( you must have seen it comming out of volcanoes it's very hot and will burn your body)
so my friend your idea won't work as the air which will come out of the U pipe would be very hot .

Answer 6

It would be cooler then the air temp. In Australia in the desert they have built homes underground to protect them from the heat

Answer 7

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Answer 8

100 - 200 = -100F

The temperature will be -100F.

Well... its as good as your going to get...