> you only need to go down 10 ft or so before you hit the average annual temperature

Is this because of geothermal energy leaking upwards? If so, it's not the dirt, it's the geothermal energy.

> Is this because of geothermal energy leaking upwards

No. The heat energy comes from the sun. Power flux from geothermal is measured in milliwatts per square meter, while the sun can provide more than a kilowatt during the day. So real geothermal heating is negligible at the surface. That's why the temperature a few feet down equals the average annual temperature at the surface.

The only reason people call this "geothermal" is because marketing people realized that this sounds more impressive than "ground source heat pump". It really should not be called "geothermal", because that's something very different. Real geothermal involves extremely deep drilling (not feasible for residential use) or unusual geology.

	▲	westurner 2 days ago \| parent [-]
		Geothermal energy: https://en.wikipedia.org/wiki/Geothermal_energy Geothermal heating > Extraction (GCHE, GHX) \|\| Ground source heat pump (GSHP) https://en.wikipedia.org/wiki/Geothermal_heating GSHP: Ground source heat pump: https://en.wikipedia.org/wiki/Ground_source_heat_pump Heat pump: https://en.wikipedia.org/wiki/Heat_pump #Types : > Air source heat pumps are the most common models, while other types include ground source heat pumps, water source heat pumps and exhaust air heat pumps. Heat pump > Types: - SAHP: Solar-assisted heat pump; w/ PV - acronym for a heat pump with TPV thermophotovoltaic heat to electricity: - acronym for a heat pump with thermoelectric heat to electricity: - TAHP: Thermoacoustic heat pump - ECHP: Electrocaloric heat pump Electrocaloric effect > Electrocaloric cooling device studies: https://en.wikipedia.org/wiki/Electrocaloric_effect#Electroc... GCHE, GHX: Ground-coupled heat exchanger: https://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger Acronyms! From https://www.google.com/search?q=Ground-coupled+heat+exchange... : HGHE: Horizontal Ground Heat Exchanger: a GCHE installed horizontally e.g. in trenches VGHE: Vertical Ground Heat Exchanger: GCHE installed vertically e.g. in boreholes or piles. PGHE: Pile Ground Heat Exchanger: A specific type of GCHE that is integrated into the structural foundation piles of a building. Solar chimney or Thermal chimney: https://en.wikipedia.org/wiki/Solar_chimney OTEC: Ocean Thermal Energy Conversion: https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversio... and the ecological salinity gradient: FWIU archimedes spiral turbines power some irrigation pumps in Holland at least. Is there an advantage to double/helical archimedes spirals in heat pumps if/as there is in agricultural irrigation? Screw turbine: https://en.wikipedia.org/wiki/Screw_turbine Noiseless double-helical Achimedes spiral wind turbine on a pivot like a pinwheel: Liam F1 average output with 5m/s wind: 1500 kWh/yr (4.11 kWh/day); Weight: ~100 kg / ~220 lbs; Diameter: 1.5 m / 4.92 ft What about CO2 and heat pumps? Would a CO2 heat pump make sense? Absorption Heat pump (AHP) https://en.wikipedia.org/wiki/Absorption_heat_pump Adsorption Heat pump (AHP) CO2-Sorption Heat Pump: a Adsorption Heat pump (AHP) that uses CO2 as the adsorbate. NISH: Nano-Ionic Sorption Heat Pump; with e.g. sustainable hydrogels Is it better to just recover waste heat from other processes; in a different loop? LDES heat pump Supercritical CO2 heat pump Aerogels don't require supercritical drying anymore, There's also buoyancy. The pyramid builders may have used buoyancy in a column of heated bubbly water to avoid gravity, in constructing the pyramids as a solar thermohydrodynamic system with water pressure.

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werdnapk 2 days ago | parent | prev | next [-]

Yes, the you can put "thick" insulation over top of any buried plumbing and the exposed bottom will gain geothermal heat from the below and it can prevent freezing.

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adverbly 2 days ago | parent | prev | next [-]

Its a bit of both, but its primarily due to the high insulation.

There are 2 gradients: The surface gradient is what I mentioned about and its quite steep(only a few meters to drop tens of degrees). After that, you reach approximately the average annual surface temperature, but do continue to get small drops due to the geothermal gradient. The geothermal gradient is relatively shallow - you need to go down a thousand meters to see tens of degrees drop.

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vasco 2 days ago | parent | prev [-]

Had the same thought, we'd have to put a thermometer inside a 10ft cube full of dirt for science.

	▲	profsummergig 2 days ago \| parent [-]
		> a 10ft cube full of dirt suspended in air