# Inorganic Salt Hydrate for Thermal Energy Storage
## 5 Application
### Salt Hydrates for Wallboards  
With the increasing emission of carbon dioxide, blending PCMs in building materials or directly using PCMs as wall boards, is able to store considerable energy during the daytime at high temperature and release energy at night when temperature is low by melting and solidifying processing. The combination of PCMs with building materials has showed superior performance which can contribute to energy saving, electricity shifting and human comfort [70; 76; 77; 78; 79]. Figure 4a showed a schematic of a kind of full-scale room with PCM concrete wallboards. As seen in Figure 4b, the effects of alleviating temperature fluctuation of a kind of PCM wall room compared with ordinary room are apparent [80]. However, PCMs used in construction field has certain requirements in terms of phase change temperature, stability, strength and price. Consequently, it is a significant step to choose suitable materials and methods of building envelope enclosures, as it is a major parameter to decide by what extent the thermal mass is activated. High fusion heat, odorless and nontoxic properties make salt hydrates be good candidates for construction energy saving.  
Figure 4: _Cont._  
Figure 3: (a) Solar thermal collectors (b) Hot-water tanks with PCM modules. Reproduced with permission from [74]. Elsevier: Solar Energy Materials and Solar Cells, copyright 2006.  
In early years, [PERSON] [81] mixed Na\({}_{2}\)SO\({}_{4}\)\(\cdot\)10H\({}_{2}\)O with porous concrete. Due to the formation of strong hydrogen bond, composite PCMs concrete system showed high stability and it could be further applied to floor construction. Large absorption area of autoclaved porous concrete was also observed. [PERSON] et al. [82] carried out a detailed study on thermal properties of artificial climatic chamber with CaCl\({}_{2}\)\(\cdot\)6H\({}_{2}\)O/expanded graphite composite panels at different position. Figure 5 showed the PCM panel packed by polyvinyl chloride (PVC) panel followed by compacting. Four pieces of the PCM panels were fabricated by the same process to use as wallboards. The thermal performance of the test room equipped with the PCM panels at each position was evaluated by placing the room in an artificial climatic chamber. It was revealed that both elements of position and quantity could influence thermal performance of the testing rooms. Moreover, numerical modeling verified the experimental investigations, and better performance of CaCl\({}_{2}\)\(\cdot\)6H\({}_{2}\)O was found comparing with organic (RT27/EG composite PCM) panel. This success model showed that radiative effects of salt hydrate wallboards could evidently enhance thermal comfort of residents. Recently, [PERSON] et al. [83] developed a novel nonflammable CaCl\({}_{2}\)\(\cdot\)6H\({}_{2}\)O/expanded perlite composite and then fabricated into a board for replacing the foam board to be employed as the core in a foam insulating brick to obtain a PCM board. It is found that when applied PCM brick as the roof of a test room, the indoor peak temperature decreased more apparently compared with foam brick.  
Figure 4: (**a**) The schematic of a full-scale experimental room with PCM; (**b**) Temperature comparison of ordinary wall room and PCM room. Reproduced with permission from [80]. Elsevier: Energy Procedia, copyright 2017.  
Figure 5: Photographs of the panels without (**left**) and with the CaCl\({}_{2}\)\(\cdot\)6H\({}_{2}\)O /EG composite PCM (**right**). Reproduced with permission from [82]. Elsevier, Applied Energy, copyright 2017.