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Technology / How fast do earth temperatures change in the surface layer?
« on: 28/12/2022 04:42:34 »
I am trying to evaluate the design of some wells for a ground source heat pump, and would like to know how fast soil/rock temperatures change with depth from the surface -- in the first 500 feet / 150 m. I know the first 2m or so is fairly rapid, but what happens below that? In our area (western Montana, USA, elev. ~4200'), "ground temperature" is supposed to be about 43 °F, but it is unclear to me where that figure comes from, and there is an obvious non-linear change as depth increases. I have an existing heat pump with 5 wells 200' deep, and another family member down in Colorado, at elevation ~8500', has one with 3 wells 350' deep.