Direct Heat Applications of Geothermal Energy Resources and the Second Law of Thermodynamics

Abstract

The Second Law of Thermodynamics is the proper measure of efficiency in end use of energy resources. The available work content of energy resources is a function of the temperature difference from ambient. The efficiency in utilization of this available work depends on the degree to which characteristic end use temperature requirements are matched to the characteristic temperatures of available work content of energy resources. The characteristic temperature needs of more than 42% of present national end use of energy resources is less than 150° centigrade. Geothermal resources may have available work at temperatures of from 15° to 150° centigrade in the amount of from 640 to 1935 QUADS out of a total of from 735 to 2404 QUADS. On this basis the greatest efficiency o fuse of the available work content o from than 80% of all identified or expected geothermal resources is for direct heat applications in district heating, commercial and industrial process and space heating. Furthermore, deposits of low temperature geothermal energy are well situated for potential retrofit and new direct heat applications.