Recent advancements in low-energy buildings: Integrating bio-phase change materials and rooftop greenery systems

Buildings are a major part of sustainable urban development. The need to increase the energy efficiency of buildings is attested by the growing demand for energy usage and emission reduction targets. This review identifies the significance, challenges, and mitigation strategies for the energy performance of buildings. The individual and combined abilities of bio-phase change material (bio-PCM) and rooftop greenery systems (RTGS) as building envelopes on building energy performance are critically reviewed and discussed accordingly. The literatures revealed that implementing bio-PCMs and RTGS as building envelopes can significantly increase building thermal performance, thermal comfort and reduce energy. Annual reduction in energy utilization was reported at 28 % while using bio-PCM as building envelope with approximately 17 % drop in thermal load demand. RTGS has been known to reduce heating and cooling demands, with studies showing up to a 45 % drop in air-conditioning energy demand in hot, sub-humid and warm regions with a temperature drops of up to 10 °C in the summer season. A simulation-based study has shown approximately 13.5 % energy savings in subtropical Queensland, Australia, when using RTGS. Integrating cool roofs with PCMs in a study led to findings suggesting 46 % and 25 % energy savings in Australian cities Sydney and Darwin respectively. In the sub-tropical climates of Rockhampton, the energy savings was noted to be 30 %. This review points toward the unexplored potential of energy-efficient technologies and implementation techniques, which will certainly aid in the lack of advancement towards sustainable and energy-efficient building designs, particularly in subtropical climates. This study will provide essential information to builders, developers, and policymakers for applications of combined bio-PCMs and RTGS in buildings.