# Energy Saving Potential of PCMs in Buildings under Future Climate Conditions
## 2 Background
### Application of PCMs in Buildings  
Air conditioning systems in buildings represent a significant part of global energy use. Therefore, it is necessary to improve the energy performance of buildings, which can be achieved by passive means in the building envelope [6] or active means with smart HVAC equipment [7]. The building envelope regulates the heat exchange between the indoor and outdoor environments and greatly affects building energy requirements and the thermal comfort of occupants. In addition, it has potential to integrate new materials and systems. PCMs are a promising strategy for improving the energy performance of buildings through their high energy storage capacity. When PCMs are incorporated into a building envelope (in the walls or other components [19]), they can store and release energy as latent heat in short temperature ranges, which results in a large increase in the building's thermal mass [33]. PCM application in buildings reduces heating and cooling loads and carbon emissions and provides excellent living comfort [20; 34; 35]. A considerable number of researchers have published studies about the application of PCMs in buildings. [PERSON] et al. [36] investigated the use of microencapsulated PCMs on concrete walls. Their experimental results showed that the indoor temperature of the PCM-enhanced concrete building was 1 \({}^{\circ}\)C lower than that of the building without PCM. In addition, the maximum temperature in the space with the PCM-enhanced wall shiftedby two hours. [PERSON] et al. [37] showed that integrating a thin PCM layer into the walls of residential buildings modified the heat flow fluctuations as well as the temperature. Their experimental results showed 30-40% of the peak heat flux reductions, a 2-6 h delay in the peak heat flux, and maximum daily heat transfer reductions of 3-27%. [PERSON] et al. [38] found that applying a PCM to the drywall in a lightweight steel-framed building improved energy efficiency by 10-60%, depending on the climate zone. [PERSON] and [PERSON] [19] reported that the peak heating and cooling loads of a building decreased depending on the type and phase change temperature of the PCM used. A study in New Zealand reported that using a high-melting-point PCM with an underfloor heating system led to an important shift in peak loads. In addition, using a low-melting-point PCM in the walls and ceiling provided the comfort needed in the building [39]. [PERSON] et al. [16] found that the optimal melting temperatures for internal PCMs are affected by the indoor air temperature, whereas the optimal melting temperatures for external PCMs are affected by the outdoor air temperature. A passive PCM heating and cooling system is a sustainable way to ensure thermal comfort and reduce the heating and cooling demand in buildings. For example, a study in Australia identified the ability of PCMs to reduce HVAC demand in main Australian cities. Those results showed that applying PCMs in buildings would decrease diurnal and nocturnal temperature fluctuations and increase the thermal comfort of occupants [40]. Another study investigated the energy savings from applying PCMs to lightweight steel-framed buildings in EU climates; those results suggest that applying PCMs to the walls improved the energy performance in all EU climates [41]. [PERSON] et al. [42] described how using PCMs in a passive house would decrease overheating in the summer by significantly reducing the hours of overheating in a specific area and thereby improving thermal comfort. [PERSON] et al. [3] described applying a PCM with a high melting point to building envelope models and found that they improved the heating and cooling energy performance and achieved high energy savings. A study in Chile evaluated the influence of PCMs on energy performance in relocatable lightweight buildings under different weather conditions. Those results showed that energy saving potentials are limited in tropical and snow climate regions and acceptable in arid and warm temperate climates [4].