Abstract
To utilize geothermal energy from hot springs, an organic Rankine cycle/vapor compression cycle (ORC/VCC) system was employed for air conditioning and a thermodynamic model was developed. Six working fluids, R123, R134a, R245fa, R600a, R600 and R290, were selected and compared in order to identify suitable working fluids which may yield high system efficiencies. The calculated results show that because of high system pressure for R290 and R134a, R600a is the more suitable working fluid for ORC in terms of expander size parameter, system efficiency and system pressure. In addition, R600a is also the most appropriate working fluid for VCC in terms of pressure ratio and coefficient of performance. R600 and R600a are more suitable working fluids for ORC/VCC in terms of overall coefficient of performance, refrigerating capacity per unit mass flow rate and chilled water yield from per ton hot water. In sum, R600a is the most suitable working fluid for ORC/VCC through comprehensive comparison of ORC efficiency, expander size parameter, pressure ratio, coefficient of performance, system pressure and chilled water yield from per ton hot water for six different working fluids. However, the flammability of R600a should attract enough attention.
Highlights
To utilize geothermal energy from hot springs, an organic Rankine cycle/vapor compression cycle (ORC/VCC) system was employed for air conditioning and a thermodynamic model was developed
There are a lot of hot springs in the world, many of which exceed 70°C (Lund et al 2005, 2011), while the proper bath temperature at the hot spring hotel is generally in the range of 30°C to 50°C, which causes the heat energy to be rejected to the atmosphere if the water temperature of the hot spring is higher than the bath temperature, resulting in greater waste of energy and the existence of thermal pollution in the surrounding environment
Most of the hot spring hotels need air conditioning. Making use of these waste heats from hot springs released to the environment for air conditioning is of great significance
Summary
To utilize geothermal energy from hot springs, an organic Rankine cycle/vapor compression cycle (ORC/VCC) system was employed for air conditioning and a thermodynamic model was developed. Making use of these waste heats from hot springs released to the environment for air conditioning is of great significance. Some effort has been devoted to the utilization of the vast amount of waste energy for refrigeration or air conditioning. Heat-operated absorption/adsorption systems can utilize waste heat for refrigeration or air conditioning (Lu et al 2013; Luo et al 2012). Wang et al (2013) studied an absorption air-conditioning system driven by a low-grade geothermal heat source. Davis and Wu (1997) used a finite-time thermodynamic approach to analyze a geothermal-powered low-temperature Rankine cycle for air conditioning. Kececiler et al (2000) designed an absorption refrigeration system with geothermal energy and experimentally analyzed its performance
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