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The study aims to enhance the reliability of direct thermal energy storage (TES) using phase change materials (PCMs) and nanoparticles, ensuring sustained heat supply even during periods of low or intermittent solar radiation. The study specifically investigates a TES system comprising a double-cylindrical shell container with two distinct PCM types: petroleum jelly or petrolatum with 1 % Al2O3 nanoparticles by volume in the outer shell and wax in the inner shell. Additionally, a redesigned heat exchanger is employed to improve heating efficiency. The study examines two configurations: an open system and a closed system with a storage water tank. The deliberate strategy of augmenting PCM volume is aimed at enhancing heat transfer during both the charging and discharging phases. The performance of closed and open system configurations is compared, with a focus on highlighting the temperature profiles during the charging and discharging processes. The incorporation of 1 % Al2O3 nanoparticles in the PCMs led to a significant enhancement in efficiency, with the two-phase materials case achieving the highest efficiency of 73 %. Furthermore, the utilization of nanoparticles resulted in an improvement in efficiency of approximately 5 %. These findings demonstrate the potential of using dual PCM layers with NPs additives in direct TES systems.

A mathematical model was developed to investigate the effect of crucial operating parameters, such as process inlet humidity ratio, inlet volume flow rate, R/P ratio (reactivation/process air flow), regenerative temperature and rotational speed on the performance of desiccant wheels in hot and humid climates, using wound silica gel and molecular sieve desiccants. The desiccant wheels were designed to operate in two modes, specifically, with 90° for reactivation and 270° for process (1:3 split) as well as with 180° for reactivation and 180° for process (1:1 split). The main results enabled to make the following observations: (i) higher regeneration air temperature leads to an improvement of dehumidification and reduction of the thermal coefficient of performance COPth, (ii) an increase in the process inlet volume flow rate causes a reduction in the process removed moisture; (iii) the greater R/P ratio is required to remove more moisture, while a lower R/P ratio implies the lower power consumption for regeneration; (iv) silica gel desiccant is preferred when greater moisture removal is required at high inlet relative humidity, while molecular sieve desiccant is preferred when low dew point is required at low inlet relative humidity. Keywords: Moisture, Desiccant, Cooling system, Silica gel, Molecular sieve, Indoor humidity