Performance comparison of a two-bed solar-driven adsorption chiller with optimal fixed and adaptive cycle times using a silica gel/water working pair

The previously published studies based on the performance prediction of solar-powered adsorption chillers incorporate a fixed cycle time which is either prespecified, or determined as a result of a numerical optimization procedure. However, the cycle time of a solar-powered commercial adsorption chiller cannot be expected to remain constant with the number of cycles owing to the continuously varying intensity of solar radiation from sunrise till sunset. This paper presents the first attempt of comparing the numerically predicted performance of a solar-powered two-bed silica gel/water adsorption chiller based on adaptive and fixed cycle time conditions using a two-stage iterative optimization. The adsorption/desorption (ads/des) stage for the adaptive cycle time condition is terminated as soon as the ads/des uptakes reach their corresponding equilibrium values, while the preheating/precooling (PH/PC) stage is ended as soon as the vapor pressure gradient inside either of the two beds becomes negligibly small. The optimal ads/des as well as the PH/PC times for the adaptive cycle time condition have been used as a baseline for maximizing system performance for the fixed cycle time condition using a two-stage iterative optimization, and the two optimized cycle time conditions have been compared in the context of commercial applications.