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Abstract In this study a compound parabolic collector (CPC) taken from literature was investigated optically and thermally through simulation. The collector was tested at different transversal and the longitudinal incident angles and the results showed us a total agreement between the present and the previous study where TracePro software was used. In addition, a new optical efficiency relationship was proposed and it was found that diverges significantly from the commonly used relationship as the reflector's shape losses and/or the absorber's diameter increase. Also, the CFD analysis results were validated from the previous study experimental data (4.2% mean divergence in thermal efficiency), something that reveals how sufficiently the real problem has been approached. Finally, an optimization process was followed in order to improve the collector's optical performance, while the novel CPC resulted from the optimization was compared with the initial design for the typical conditions of the 11th of June in Athens from 08:00 to 16:00, in order to examine the effect of different solar irradiation intensities in the comparison process. It was revealed that the novel design exceeds the initial one in all the examined hours. The design and the simulation of the collector were conducted via Solidworks Flow Simulation software. Highlights • A new optical efficiency relationship is proposed. • The previous ray tracing agree with the present one (2.9% and 1.8% mean deviations). • The simulation results diverge 4.2% on average from the experimental one. • The present simulation exceeds the previous theoretical solution in accuracy. • The novel design enhances the optical efficiency by 2.4% regarding a daily operation. [ABSTRACT FROM AUTHOR]

Solar energy utilization for covering the heating loads of buildings is an innovative and clean way which leads to lower electricity consumption. Passive heating systems are low-cost and simple technologies which are able to cover a great part of the space heating demand. Trombe wall is the most mature technology for capturing solar irradiation and transferring it inside the building in order to cover a part of the heating loads, especially the hours after the noon. In this study, an innovative Trombe wall with an extra window in the massive wall is suggested. This wall is compared with the conventional Trombe wall and the usual insulated wall in order to make a complete investigation. The examined walls are located in south direction, in order to maximize the impact of solar irradiation. According to the final results, the new Trombe wall is the most appropriate technology, creating warmer indoor profile than the other cases, especially the hours between noon and afternoon. The analysis in performed with the commercial software Solidworks Flow Simulation and the examined building is located in Athens, Greece. [ABSTRACT FROM AUTHOR]