Windows let sunlight into the indoor spaces that significantly contribute to healthy indoor environments. Windows are typically made of high-heat conductive materials with relatively low thermal capacities that make them the weakest component of building envelopes. Integrating Phase Change Materials (PCMs) into the window structure is an effective method to increase the thermal resistance of the windows. PCM is an organic material with a wide range of melting points, typically between 20 o C and 70 o C. During the melting process of PCM, a large quantity of energy is absorbed, behaving like a thermal barrier. However, the fixed PCM melting point makes it effective only in a certain outdoor temperature range and window-facing direction. To tackle this problem, dual PCMs with different melting points are integrated in the window structure. The effectiveness of the integration is evaluated numerically, and the results are compared with a window with a single PCM and without PCM. The numerical results are verified and validated using experimental results obtained from a window with single PCM. The thermal effectiveness of the window with PCM is assessed in two summer months, May and August, and PCM with lower-melting point (n-Octadecane, T m =27.5°C) and higher-melting point (n-Eicosane, T m =37.5°C) are used in this study. PCM with lower melting point performs the best in May, and the heat gain reduction is between 24.2% and 38.4%, depending on the window’s facing direction. However, PCM with higher melting point, performs the best in August, and the heat gain reduction is between 9% and 11.5%. When dual PCMs are used, the results show that the window with the dual PCMs is effective in both months and for all window-facing directions, and the heat gain reduction is between 4.4% and 25.9%. However, its performance does not exceed that of the best single PCM window in either May or August.
Alawadhi et al. (2026) studied this question.