Non-conventional thermodynamic converters for low temperature geothermal application

Non-conventional thermodynamic converters suitable for low-temperature geothermal applications have been considered in the present paper. The first type, called a thermogravimetric system, TG, runs with a direct cycle: this is capable of transforming thermodynamic energy into mechanical-electric energy. The second type, called a thermogravimetric heat pump, TGHP, works with an inverse cycle. In this case the mechanical energy is supplied to the system through a feed pump and not by a compressor as in a conventional plant: heat is delivered within a range of 50–80 C. The values of the cycle extreme temperatures make a TGHP appear more promising than a thermogravimetric system and therefore it has been analysed in more detail. In particular, a regenerative TGHP is characterised by COP values that are larger than those of a TGHP in its basic configuration and, furthermore, such values are larger than those of a conventional heat pump. In the present investigation, both the thermogravimetric system and the TGHP use demineralized water as a carrier fluid. Due to the environmental impact and other basic reasons, PP 50 (C5F12) and HFC 134a (C2H2F4) at present appear to be the most promising working fluids. # 2003 CNR. Published by Elsevier Science Ltd. All rights reserved