Development of a stable inorganic phase change material for thermal energy storage in buildings

• Published in: Solar energy materials and solar cells Vol. 208; p. 110420
• Main Authors: Bao, Xiaohua, Yang, Haibin, Xu, Xiaoxiao, Xu, Tao, Cui, Hongzhi, Tang, Waiching, Sang, Guochen, Fung, W.H.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.05.2020; Elsevier BV
• Subjects: Building envelopes; Buildings; Calcium chloride; Computer simulation; Construction materials; Crystallization; Differential thermal analysis; Differential thermogravimetric analysis; Energy consumption; Energy storage; Flake graphite; Flakes; Fourier transforms; Graphite; Industrial grade calcium chloride hexahydrate; Infrared spectroscopy; Latent heat; Mathematical models; Payback periods; Phase change material; Phase change materials; Phase transitions; Polymers; Scanning electron microscopy; Segregation; Solar energy; Solar radiation; Storage systems; Super absorbent polymer; Superabsorbent polymers; Supercooling; Thermal analysis; Thermal conductivity; Thermal energy; Thickening agents; Supercooling; Phase change material; Super absorbent polymer; Segregation; Flake graphite; Industrial grade calcium chloride hexahydrate
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2020.110420

Building energy consumption is influenced evidently by solar radiation. To achieve a stable indoor temperature by minimizing the heat fluctuations resulted from solar radiation, latent heat thermal energy storage systems with phase change materials (PCMs) in building envelope have been studied. Though inorganic PCMs have promising potential applications among all kinds of PCMs, the supercooling and segregation are the major issues which have restricted their practical applications. The purpose of this study is to lessen the supercooling degree of an industrial grade PCM (CaCl2·6H2O) by using a nucleating agent - flake graphite. A super absorbent polymer (SAP) was also used as a thickener to prevent segregation of CaCl2·6H2O during phase transition. The combined method of thermogravimetric analysis/differential thermal analysis (TGA-DTA) was firstly proposed to evaluate the segregation of inorganic PCM innovatively. The results showed that using 0.5 wt% flake graphite not only eliminated the supercooling of CaCl2·6H2O, but also improved its thermal conductivity for better thermal performance. The results of Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) demonstrated that the flake graphite did play an important role on the crystallization of CaCl2·6H2O. Numerical simulation demonstrated that using modified CaCl2·6H2O within walls of buildings in Hong Kong and Changsha are economically feasible with the payback periods of 18.3 years and 8.4 years respectively. [Display omitted] •The supercooling degree of CaCl2·6H2O can be reduced to less than 1 °C with the addition of 0.5 wt% flake graphite.•The addition of 25 wt% SAP can eliminate the segregation of CaCl2·6H2O.•The combined method of TGA-DTA can evaluate the segregation of CaCl2·6H2O effectively.•Using modified CaCl2·6H2O in buildings is economically feasible with the payback period of 15 years.