Examples of United States Geothermal District Heating Systems

Abstract

There are 18 geothermal district heating systems in the United States. These systems use geo-thermal fluids from 59 to 103'C, with peak flow rates from 5 to 250 Us. Installed power varies from 0.2 to 31 MWt, and annual energy use from 0.6 to 22 GWh. Thus, the total installed power is almost 100 MWt and the annual energy use is 168 GWh. Both open and closed distribution systems are used--the later type using a secondary fluid to supply the heat to the customers. Approximately half of the systems use a central mechanical plant containing heat exchangers, circulating pumps, expansion tanks and controls. Both volume and energy metering systems for customer billing are used. A variety of geothermal fluid disposal systems are used, including injection and disposal in a nearby river or stream. The energy and environmental savings, as compared to fossil fuel, amount to nearly 135,000 barrels of oil equivalent annually (20,200 TOE), and a reduction of 58,000 metric tons of carbon (coal) or 12,000 metric tons of carbon (natural gas) per year. Three systems are described.