Recent architectural trends in high-rise residential buildings are favoring more transparent facades with fully glazed exteriors. While aesthetically pleasing, high window to wall ratios (WWR) entail significant discomfort due to higher solar heat gains and heat losses. In this architectural context, passive latent heat thermal energy storage (LHTES) is a possible solution to regulate indoor thermal comfort by limiting the room temperature swings. This study investigates the effectiveness of adopting Phase Change Materials (PCMs) in retrofitting high-rise apartments with 80% WWR. A composite PCM system, comprised of two PCM products with melting temperatures of 21.7 degrees C and 25 degrees C is introduced to provide thermal energy storage across the year. The phase change cycle of the PCMs and their impact on indoor air and interior building surface temperatures are assessed. For this, two test cells were constructed, one acting as a baseline and another enhanced with the composite PCM system positioned on the walls and the ceiling. The results indicate improved performance of the test cell containing the composite PCM system in lowering peak indoor and surface temperatures up to 6 degrees C. The melting and solidification patterns of the PCMs showed a close correlation with peak solar heat gain and heat loss periods respectively. The benefits of the PCMs were more pronounced in stabilizing indoor cell temperatures in extreme conditions with sharp temperature variations. Aspects such as the effectiveness of night natural ventilation and shading design optimization were also assessed. (C) 2019 Elsevier B.V. All rights reserved.