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• Four different heat pump systems (CVI-1S, CVI-SR, CVI-2S and CVI-3S) are analyzed. • The COP of each heat pump is maximized by optimizing the heat pump design. • The optimizations involve 167 fluids as possible refrigerants in the heat pumps. • The optimal fluids and the maximal COP are reported in charts. • The refrigerants dme, r161, r40, cf3i, r435a, r510a are among the best fluids. In this paper, numerical optimization analyses are performed for four distinct heat pump systems, namely, the CVI-1S, CVI-SR, CVI-2S and CVI-3S systems. These analyses are performed for various combinations of hot side and cold side temperature values (i.e., for hot side temperatures ranging from 25 °C to 60 °C, and for cold side temperatures ranging from -40 °C to 10 °C). A total of 167 fluids are compared in order to obtain the highest COP value, for each temperature combination investigated. A robustness analysis is also achieved so as to identify the fluids that provide a COP value larger than 95% of the maximal COP value. Results are presented as charts that allow identifying the best fluids and the most robust fluids for each heat pump system. The results show that heat pump systems involving more equipment or including separators are more efficient than the others. Moreover, the results show that the refrigerants dme, r161, r40, cf3i, r435a and r510a are among the most robust fluids for all heat pump systems investigated. [ABSTRACT FROM AUTHOR]

In this paper, three different modifications of the basic Rankine thermodynamic cycle are proposed. The objective is to increase the thermal efficiency of power systems based on Rankine cycles. The three new systems are named “Rankine-1SCR”, “Rankine-2SCR”, and “Rankine-3SCR” cycles, and they consist of linking a refrigeration cycle to the basic Rankine cycle. The idea is to use the refrigeration cycle to create a low temperature heat sink for the Rankine cycle. These three new power plant configurations are modeled and optimized with numerical tools, and then they are compared with the basic Rankine cycle. The objective function is the thermal efficiency of the systems (i.e., net power output (kW) divided by heat rate (kW) entering the system), and the design variables are the operating temperatures within the systems. Among the 84 × 84 (i.e., 7056) possible combinations of working and cooling fluids investigated in this paper, it is shown that: (i) the Rankine-1SCR system is advantageous for 1338 different fluid combinations, (ii) the Rankine-2SCR system is advantageous for 772 different fluid combinations, and (iii) the Rankine-3SCR system is advantageous for 768 different fluid combinations. [ABSTRACT FROM AUTHOR]

• Dual pressure transcritical ORC is usually the best in the range of conditions tested. • Specific work output between 5 and 70 kJ/kg were obtained from simulations. • Five fluids (R218, R115, R227ea, RC318, RE245cb2) stand out in the optimization. • Optimal values of cooling tower range are lower at colder brine and hotter cold sink. • Parasitic loads (pumps, cooling) range from 15 to 45% of the gross power produced. Four variants of the Organic Rankine Cycle (ORC) applied to geothermal power plants are optimized by means of numerical tools. These variants are: (i) the subcritical ORC with single-pressure heater (ORC/S/SC), (ii) the transcritical ORC with single-pressure heater (ORC/S/TC), (iii) the subcritical ORC with dual-pressure heater (ORC/D/SC), and (iv) the transcritical ORC with dual-pressure heater (ORC/D/TC). All the systems are recuperative and include a wet cooling tower. The objective function is the specific work output and design variables include operating pressures, mass flow ratios between the brine and the working fluid, superheaters effectiveness and cooling tower range. The systems are optimized for 20 different potential working fluids. The optimization is performed for inlet brine temperatures from 80 to 180 °C, and for ambient air wet bulb temperatures from 10 to 32 °C. The results show: (i) the superiority of ORC/D/TC for most of the cases, (ii) the relevance of using a dual-pressure heater at high sink temperature and low brine temperature, and (iii) the importance of choosing the right cooling tower range for an optimal power plant design. [ABSTRACT FROM AUTHOR]