Low temperature geothermal systems

In low temperature geothermal systems, where temperatures are below 140° C, direct production of electricity from vapour is not generally convenient. However, if temperatures are above 90° C it is possible to use warm fluids to vaporise a second fluid that has a lower boiling temperature (such as freon, isobuthane or ethyl cloride), thus obtaining vapour for indirect electricity production, even if the productivity level of this process is rather low.
Hot waters though lend themselves to a variety of uses, with a “cascade” scheme, that first uses hot fluids in applications that require higher temperatures, and then reuse them, in applications that require lower temperatures, as they get cooler.
Its primary application is for urban heating, for which water between 130° C and 50° C can be used. Hot water fields are used for domestic heating in various states around the world, especially, in order of importance, in Japan, China, Hungary, ex- URSS, Iceland, Poland, France. The first experiments of geothermal heating for domestic usage took place in Iceland in 1930: in this country, a significant part of the capital’s houses heating comes from low-energy geothermal fields. In Italy this method is applied, for example, to hotels in the thermal area around Abano Terme (Colli Euganei, Veneto) and many buildings around Larderello (Tuscany).

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