Downhole heat exchanger

A downhole heat exchanger, (DHE) also called a borehole heat exchanger, (BHE) is a heat exchanger installed inside a vertical or inclined borehole.[1] It is used to capture or dissipate heat to or from the ground. DHT's are used for geothermal heating, sometimes with the help of a geothermal heat pump. Downhole heat exchangers, like other use of geothermal energy, have the potential to significantly contribute to the reduction of CO2 emissions.[2] In northern Europe, DHE are already widely deployed.[3]

Drilling process for a Downhole heat exchanger. Furled tube in the foreground on the left.
Bottom end of a Downhole heat exchanger
Top end of a Downhole heat exchanger

Types

U-tube

The heat exchanger usually consists of one or two u-tubes through which the carrier fluid, usually water, circulates. The space around the u-tubes is filled with groundwater or backfilled with thermally conductive grout.

Open pipe

Another design uses a single open pipe to flow water downward. The water then returns through the annular gap between the pipe and the casing. This design provides better thermal contact than u-tubes, but risks contamination by groundwater. Since this involves practically no downhole equipment, these systems usually only go by the name of borehole heat exchangers (BHT).

Standing column well

If no casing is installed and groundwater is permitted to charge the system, this arrangement is no longer a BHT, but rather a standing column well.

References
  1. "Downhole Heat Exchangers" (PDF). Geo-Heat Center - Oregon Institute of Technology. Retrieved 21 April 2013.
  2. "Geothermal Energy - Professur für Geothermal Technologies". www.bgu.tum.de. Retrieved 2021-01-15.
  3. https://www.mbie.govt.nz/assets/14861fe5a3/geothermal-barriers-update-1.pdf
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