8.3 Types of geothermal energy use

This chapter describes different types of geothermal energy use. The geothermal energy can be used directly, i.e. without any further conversion, as heat. The direct application of geothermal heat is referred to as direct use. In direct use, geothermal energy is employed directly as heat without further conversion in other types of energy. In moderate and cold climates, most of the national final energy is consumed as heat. As an example, it is found in Germany in the year 2002, about 58% of the national final energy was consumed for space heating, process heat, and hot water. There is a variety of different Earth coupled heat extraction systems. Horizontal Earth coupled heat exchangers are pipe systems buried in the ground below the freezing depth. Shallow borehole heat exchangers commonly consist of one or several U-pipes installed and backfilled in a borehole, the most frequent configuration consisting of two U-pipes arranged at an angle of 90°. Heat exchanger pipe systems integrated directly into the concrete foundations of buildings and other constructions for heating and cooling. Deep borehole heat exchangers have been installed to depths of about 1500 m - 3000 m. Hydrothermal heating systems consist of one or several, usually deep, boreholes for producing water from aquifers or deep reservoirs. Commercial and industrial applications of direct use geothermal energy are illustrated. Geothermal power generation requires vapor to drive turbines. It can be derived as either wet or dry steam from natural reservoirs.