Advanced thermal regulating materials and systems for energy saving and thermal comfort in buildings

Building sector is responsible for 40% of primary energy use worldwide. The heating, ventilation and air-conditioning (HVAC) systems, which provide cooling and heating to maintain indoor thermal comfort, accounts for over 50% of total building energy use. Thus, HVAC systems play a crucial role in achieving energy saving and thermal comfort goals. In recent decades, advanced materials and systems are developed to regulate the thermal energy in buildings for reducing HVAC system energy consumption without compromising thermal comfort. Broadly speaking, there are mainly two strategies to apply these materials and systems for thermal regulation. One strategy is to apply them on the building envelope for regulating the heat transfer between outdoor and indoor, whereas another strategy is to apply them on the human body envelope (i.e., textile/clothing) for regulating the heat transfer between human body and the indoor environment. Existing reviews only focused on specific areas of this topic, but a comprehensive review is still lacking. To fill this gap, this article provides an overarching review covering thermal regulating strategies on both the building and human body envelopes. In each strategy, the associated materials and systems are further classified into the passive and active types. In each type, the materials and systems are discussed with respect to working principles, applications and future prospects.