Types of Heat Exchangers There are two primary styles of above-ground heat exchangers: shell-and-tube heat exchangers and plate heat exchangers.  Shell and Tube Heat Exchanger http://www.houseneeds.com/heating/hydronic-heat-supplies/aic-shell-and-tube-heat-exchanger-300000-btu-b300 Plate Heat Exchanger westank.com/plate-and-frame-heat-exchangers/ A third type of heat exchanger is a downhole heat exchanger. As its name suggests, this type is placed down in a well or borehole, and is quite simple in design. Geo-Heat Center, Oregon Institute of Technology, Klamath Falls, OR, USA Geo-Heat Center, Oregon Institute of Technology A downhole heat exchanger can be as simple as a U-loop of PEX plumbing pipe. As the schematic above illustrates, cool water or binary fluid flows inside the pipe. The temperature and density gradient promotes a convection current inside the pipe, such that cool water sinks down one side of the U, and warmed water rises up the other leg of the U. A separate pipe with perforations at either end submerged in the well alongside the heat exchanger loop can aid in creating a convection current. The downhole design has the benefit of not having to pump geothermal water at the surface.