PCMs to reduce energy consumption in buildings
A recent review article describes the principles of latent heat thermal energy storage systems using phase change materials (PCMs), and their applications to improve thermal performance in the building sector.
In 2018, the building sector accounted for the largest share of global energy consumption (36%) and global energy-related CO2 emissions (39%), with a rising demand for space cooling, according to a report by the International Energy Agency (IEA). 
Thermal energy storage (TES) systems using phase change materials (PCMs) have been investigated for building applications as a promising and sustainable option to reduce energy consumption, while maintaining a comfortable environment inside the building envelope.
According to a recent review article, PCM applications for thermal energy storage in buildings can be divided in two categories: active and passive systems. 
Active systems for thermal energy storage in buildings using PCMs
Active TES systems are characterized by forced convection heat transfer and, in some cases, mass transfer, as with a heat exchanger. Active application systems based on PCMs require mechanical equipment or an additional source of energy for operation, such as electricity for pumps or fans. These systems are best suited in cases where higher heat transfer performance or better control of the application is needed.
Active systems are primarily intended to control the indoor conditions of a building. This includes systems located inside the building envelope for heating, ventilation, and air conditioning (HVAC) and systems that are integrated in the building structure and operating through air or water distribution, as well as systems located outside the building envelope, such as storage containers for domestic hot water.
Additionally, active systems can be used for peak shaving purposes in HVAC systems, i.e. in order to reduce the amount of energy used during peak energy demand hours.
Passive systems for thermal energy storage in buildings using PCMs
Passive PCM systems exploit naturally available energy sources (e.g. solar or wind) along with the architectural design of building components to minimize the energy requirements of building operations. Passive systems minimize the use of mechanically-assisted heating or cooling systems. There is no need for additional energy input, because the heat is charged or discharged when the environment’s temperature rises or falls beyond the PCM’s phase change temperature.
Passive systems are intended to improve the thermal performance of the construction. They include PCMs that are embedded in the building materials, such as walls, floor or ceiling materials, as well as PCMs implemented as components of the building envelope, such as blinds or suspended ceilings.
For example, the authors presented a study in which PCMs had been included into building materials. With the addition of 3.2 wt.% and 2.7 wt.% PCM to cement and concrete, the building's power consumption was reduced by 11% and 15%, respectively, in a 23 °C environment.
 Global Alliance for Buildings and Construction, International Energy Agency and the United Nations Environment Programme. 2019 global status report for buildings and construction: Towards a zero-emission, efficient and resilient buildings and construction sector. https://www.iea.org/reports/global-status-report-for-buildings-and-construction-2019
 Podara, C.V.; Kartsonakis, I.A.; Charitidis, C.A. Towards Phase Change Materials for Thermal Energy Storage: Classification, Improvements and Applications in the Building Sector. Appl. Sci. 2021, 11, 1490. https://doi.org/10.3390/app11041490