THERMAL-ANALYSIS OF INDIRECT GEOTHERMAL DISTRICT-HEATING SYSTEMS

Low- and moderate-temperature geothermal resources have been discovere d in many areas of the world, and are being used increasingly for dist rict heating. Due to the corrosive action of some geothermal waters, h eat exchangers are used to avoid circulating the geothermal fluid dire ctly through the district heating systems, in what are called Indirect Geothermal District Heating Systems (IGDHS). In this case, the geothe rmal water acts as a heat source directly heating the network fluid th rough a heat exchanger. However, it is different from that of conventi onal systems in which hot water from a fossil fuel boiler is used dire ctly. In the former (IGDHS), the geothermal water is regarded as a hea t source with constant temperature, and in the latter the boiler is co nsidered a heat source with variable heat flux. This paper presents a thermal analysis of a simple IGDHS, and discusses the selection of hea t exchangers and optimum operating conditions. (C) 1997 CNR.