Extremely Low Temperature
Reservoir fluid less than 100°C is considered to to be "extremely low temperature."
Note: Sanyal classified fluids of these temperatures to be "non-electrical grade" in 2005, but electricity has since been generated from these extremely low temperature fluids so we have edited the classification title appropriately.
"The boiling point of water at atmospheric pressure, 100°C, is a reasonable lower limit for power generation from a geothermal fluid. A resource in this class is typically only suitable for non-electrical uses (reference: http://www.geothermal-energy.org/pdf/IGAstandard/SGW/2005/sanyal1.pdf).
With the advent of binary power plants this low range has actually been electrically productive in rare cases as with Alaska’s Chena Hot Springs, which uses 74°C water, the coldest water used for geothermal electrical production on earth" (reference: http://www.yourownpower.com/Power/).