Geothermal heating for the Arizona Environmental Research Laboratory greenhouses

Abstract

A preliminary study of the technical and economic feasibility of installing a retrofit geothermal heating system is analyzed for the Environmental Research Laboratory Farms greenhouse facility located in Tucson, Arizona. The facility consists of 10.6 acres of greenhouse area, of which 7.4 acres are currently operational. Natural gas or diesel fuel are presently used for heating. The maximum heating load is estimated to be 28,620,000 Btu/hr. Average annual heating energy consumption between 1974 and 1979 was 35,684 million But/year for 7.4 acres of greenhouse, costing an estimated $96,703 at 1981 natural gas prices. Two 2500 foot geothermal production wells are required, each capable of producing 1500 gpm of 130{sup 0}F water. The geothermal water is expected to contain 500 ppM total dissolved solids. Total estimated capital cost for installing the system is $902,946. The expected first year geothermal energy cost savigs are estimated to be $58,920. A simple payback of 9.1 years is calculated and the project has a net present value of $961,751. Geothermal heat could be supplied at a cost of $5.39 per million Btu in the first year of operation. The project as herein presented is marginally economic. However, it became clear after the study that an attractive economic case could be made for providing about 50 to 60 percent of the required heating load as a base load using geothermal energy.