Summary The requirement of simultaneous heating and cooling effects at different zones of a building demands for the development of an energy‐efficient air‐conditioning system for heating and cooling outputs. In order to fulfil this requirement, a novel multistage hydrogen‐alloy–based sorption heat pump (H‐A SHP) for space air‐conditioning is proposed in the present work. The proposed system produces multiple cooling and heating outputs at 20°C and 45°C, respectively, with single heat input at 160°C. A set of MmNi5, La0.8Ce0.2Ni5, MmNi4.4Al0.6, and LaNi4.6Al0.4 metal hydrides (MHs) is chosen to operate at the above‐mentioned temperature range with hydrogen as working fluid. The proposed system can completely eliminate the requirement of conventional compressor because it operates using waste heat, and useful outputs (cooling‐heating) result from reaction enthalpies (MH + H2 interaction). The thermodynamic and heat‐hydrogen transfer analyses of H‐A SHP are carried out through finite volume approach, in which heat and mass transfer equations are solved to foresee the variations in MH bed temperature, hydrogen concentration, and heat interactions during cycle operation as well as the amount of cooling and heating outputs delivered to the air‐conditioning space. The numerical code is validated with experimental pressure‐concentration isotherms (PCIs) measured through Sievert's apparatus. The maximum heat exchange during the cooling and heating processes, at a particular instant of time, is observed as 257.5 and 286.1 W with cooling temperature of 10°C and heating temperature of 53°C, respectively. The thermodynamic performance is estimated as 178.5 kJ of cooling effect, 265.5 kJ of upgraded heat with overall coefficient of performance (COP) of 6.8, and overall specific alloy output of 396.5 W/0.34 kg of alloy.

In the present study, the performance of H 2-metal hydrides-based (HSRS) and CO 2-adsorbent-based refrigeration systems (CSRS) are investigated and compared. The pair of metal hydrides (MH) used for HSRS is La 0.9 Ce 0.1 Ni 5-LaNi 4.7 Al 0.3 whereas, for CSRS, it is Activated Carbon-Pore Expanded Mesoporous Silica (PEMS) adsorbents. The above pairs are chosen due to their suitability toward the sorption refrigeration system, which results from the screening of different pairs. The performances of these systems are investigated through the thermodynamic simulation as well as computational fluid dynamics (CFD) approach. The thermodynamic cycles of both the systems are analyzed for the operating temperatures of 0 C (T r ; refrigeration), 25 C (T a ; heat sink), and 100 C (T s ; heat source). Upon thermodynamic simulation, the refrigeration output, coefficient of performance (COP), specific refrigeration power, and second law efficiency are observed as 87.04 kJ, 0.91, 24.17 W/kg, and 41.6% for HSRS whereas, it is 49.32 kJ, 0.72, 20.55 W/kg, and 33.1% for CSRS, respectively, using 0.5 kg of each alloy. The CFD simulation results in the behavior of absorbent/adsorbent beds concerning temperature and gas mass variations. The minimum bed temperature is observed to be −31 C in HSRS, which is lower than that of CSRS (i.e.,-9 C). The overall cycle time is predicted to be 3600 seconds for HSRS and 2400 seconds for CSRS. The shorter cycle time in CSRS is due to the high-pressure differential between coupled beds during reactions and higher reaction rates of adsorbent materials than metal hydrides. Though CSRS possessed shorter cycle time, HSRS is found to be more suitable for refrigeration application due to better thermodynamic performance, in the given operating temperature range. Besides, the influence of variations in operating temperatures on the system performance is investigated and obtained the optimum temperature range of T r = 5 C, T a = 20 C, and T s = 95 C. Finally, the thermodynamic performances of HSRS, CSRS, and CO 2-based vapor adsorption refrigeration system (CO 2 VARS) are compared and observed that HSRS possessed better refrigeration performance among three.

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