Sonoma State Hospital, Eldridge, California, geothermal-heating system: conceptual design and economic feasibility report

The Sonoma State Mental Hospital, located in Eldridge, California, is presently equipped with a central gas-fired steam system that meets the space heating, domestic hot water, and other heating needs of the hospital. This system is a major consumer of natural gas - estimated at 259,994,000 cubic feet per year under average conditions. At the 1981 unit gas rate of $0.4608 per therm, an average of $1,258,000 per year is required to operate the steam heating system. The hospital is located in an area with considerable geothermal resources as evidenced by a number of nearby hot springs resorts. A private developer is currently investigating the feasibility of utilizing geothermally heated steam to generate electricity for sale to the Pacific Gas and Electric Company. The developer has proposed to sell the byproduct condensed steam to the hospital, which would use the heat energy remaining in the condensate for its own heating needs and thereby reduce the fossil fuel energy demand of the existing steam heating system. The geothermal heating system developed is capable of displacing an estimated 70 percent of the existing natural gas consumption of the steam heating system. Construction of the geothermal fluid distribution and collection system and the retrofits required within the buildings are estimated to cost $1,777,000. Annual expenses (operation and maintenance, insurance, and geothermal fluid purchase) have been estimated to be $40,380 per year in 1981 dollars. The proposed geothermal heating system could then be completely paid for in 32 months by the savings in natural gas purchases that would result