Digging Deeper into Direct Use of Geothermal Energy

Below the earth’s surface is a source of heat available year-round that can be utilized to supply heating and cooling to buildings, industrial processes, agricultural applications and more: geothermal energy, which has vast potential for use in the district energy industry. There are currently two approaches used to harness these renewable geothermal resources for heating and cooling. One is geothermal heat pump technologies (also called ground source or geoexchange), which transfer heat – at relatively shallow depths – to and from the earth using the constant temperature as the exchange medium. The second is directuse geothermal technologies, which, by contrast, directly tap heat from the earth in areas where the subsurface is hot enough for use in a range of applications from sidewalk snow melting and pool heating to district energy systems. Direct-use resource temperatures are typically below 150 degrees C (<300 degrees F), which is lower than the typical temperatures of resources used for geothermal electricity generation. In addition, direct-use resources are more widely available and therefore deployable on a much larger scale than those utilized in geothermal electricity generation. In 2017, the U.S. Department of Energy Geothermal Technologies Office awarded funding to six research projects to study the feasibility of deploying largescale direct-use geothermal systems. The studies included district heating, district cooling and thermal energy storage applications.