Experimental and Numerical Investigations of a Solar PCM Heat Exchanger for Indoor Temperature Stabilization

Abstract

The mismatch between indoor daytime and nighttime temperatures in continental climates must be exploited to minimize energy consumption and greenhouse gas emissions using a solar-coupled thermal energy storage device. A phase change material (PCM) based heat exchanger (HX) for indoor temperature stabilization in continental climate zones typical of Southeast Asia is investigated in this study. Eight different cases are experimentally tested, in which the PCM HX is charged and then discharged for different humidity conditions until the indoor temperature reached 20°C using combinations of free and forced convection. The study is conducted for two different system configurations in Pakistani winters. The results reveal that Case 2, using forced convection during both the charging and discharging, provides the best thermal performance with a gradual temperature reduction during PCM discharging, an adequate discharging time of 20.5 h, and the most uniform temperature distribution in the test volume. Cases 1, 4, 5, and 7 result in indoor temperature differences of 20°C, 15°C, 15°C, and 10°C, respectively, for discharging times ranging from 8 to 10.5 h. The PCM HX maintained a temperature difference of 6°C for 12 h whilst keeping the relative humidity between 45 and 65% using forced convection of testing in an actual room. Such solar powered PCM-HX is uncommon in Southeast Asia with a potential to minimize domestic heating loads while maintaining indoor thermal comfort unlike currently used conventional heating technologies. Additionally, a comprehensive numerical study was conducted to assess the performance of the PCM HX in thermal management within the Test Volume (TV). Mesh convergence studies determined that a Fine cell size (M2) with 76,000 cells offered a balance between accuracy and computational efficiency with a deviation of just 0.5%. Temporal discretization convergence was achieved with a time step of 400ms, providing a reasonable computational period while maintaining accuracy. Numerical convergence was attained with residuals below 10-6 after 80 iterations. Consistency checks involving ten repetitions of simulations under identical conditions ensured reliability. Sensitivity analysis confirmed findings and aligned with existing literature. The numerical results were validated against experimental data, yielding negligible deviations of 4.5% for PCM temperature and 6.5% for TV temperature. Furthermore, varying test volumes (TV1, TV2, and TV3) demonstrated the PCM HX's capability to effectively manage larger volumes. In conclusion, this study combines experimental and numerical approaches to optimize PCM-based thermal management systems vi for continental climates, offering significant potential for reducing energy consumption and greenhouse gas emissions.