In the recent early period of substantial interest in alternative energy supplies just after the oil embargo of 1973, the U.3. national emphasis on the use of geothermal energy was almost exclusively directed toward production of electricity. This occurred even though there have been a number of direct geothermal operations, basically for space heating, that have been in existence for several decades and in some instances since the 1800's. More recently, it has become evident that much of our overall geothermal resource appears better suited for direct applications than for electrical production. In the last several years, there have been substantial efforts directed toward the direct use of geothermal energy for space and domestic water heating, industrial processing and, to a considerably lesser extent, cooling. Presently, geothermal energy is a practical source of energy that is being used, being planned for in quite a number of new installations and one that should be considered a candidate for "fueling" a particular operation until it is ruled out. Furthermore, space conditioning and domestic water heating represent large energy requirements that can in many instances be met more efficiently, in a thermodynamic sense, with geothermal energy systems than with the usual fossil fuel based systems.