Design and thermal performance evaluation of the thermal storage layer of a solar air collector with comprehensive consideration of six factors of phase-change materials

The heat storage layer of fully filled phase-change materials (PCM) does not melt completely, and this significantly reduces the heat storage capacity, heat -release time, output temperature difference, collection efficiency, heat peak migration ability, and PCM cost of PCM-based solar air collectors (SACs), thereby affecting the comprehensive heating requirements of building households. To solve these problems and obtain the optimal filling rate for PCM, four PCM filling schemes were designed with comprehensive consideration of the six factors of PCM. (Type I is a SAC filled with 0 % PCM, Type II is the upper portion filled with 25 % PCM, Type III is the upper portion filled with 50 % PCM, and Type IV is filled with 100 % PCM). Four models were constructed for comparative experiments. A comparative analysis of the thermal performance evaluation indices indicated that the phase-change heat storage process of the Type III thermal storage layer only uses 1.25 h to store 1.505 x 106 J of heat energy, thus indicating that Type III possesses a better heat storage capacity. The max -output temperature difference of the Type III collector decreased by 20.1 degrees C compared to that of Type I. This indicates that Type III collectors can balance the range of output temperatures and increase indoor thermal comfort. After the solar energy ceases, the continuous heat -release time of the Type III collector is 13.75 h , and the ratio of its heatrelease time to non -solar time is 94.83 % . This indicates that Type III possesses a better heat release time. The daily average heat collection efficiency of Type III filled was 37.77 % , and this was only 6.72 % higher than that of Type IV, thus indicating that Type III exhibited better heat peak migration ability, PCM utilisation efficiency, and lower PCM cost.