Parametric study on inclination angle and aspect ratio of direct absorption/storage solar collectors for building heating

Direct absorption/storage solar collectors (DASSCs) based on composite phase change materials (CPCMs) are a promising technology for efficient building heating systems. However, most existing studies focus on material modification, largely overlooking the critical influence of the collector's geometric parameters on system performance. This study addresses this gap by developing an experimentally validated numerical model to investigate the effects of inclination angle and aspect ratio on the melting behavior and photo-thermal conversion efficiency (PTCE) of a DASSC using a one-factor-at-a-time approach. The results uncover a significant trade-off between the heating rate and energy efficiency. Specifically, while an inclination angle of 45° maximizes solar irradiation intensity and accelerates the melting process by 31.2% compared to the horizontal case, it results in the lowest PTCE due to excessive sensible heat loss. Furthermore, the aspect ratio is identified as a key factor regulating the latent heat storage capacity. Reducing the aspect ratio from 13.3 to 5.0 increases the PTCE by 17.6 percentage points by improving the latent heat fraction, although this comes at the cost of a 23.5% reduction in heat storage density. These findings provide essential design guidelines for balancing melting speed, efficiency, and storage density in DASSC systems.