Thermal energy storage using phase change materials: Techno-economic evaluation of a cold storage installation in an office building

Utilizing the latent heat of solidification and melting of so-called phase change materials (PCMs) allows higher storage densities and increased process flexibility within energy systems. However, there is an existing gap in the current literature studying simultaneously the technical and economic performance of these thermal energy storages within an actual application. Thus, in this work a comprehensive techno-economic analysis of a fullscale storage with 7000 L salt-hydrate surrounding a polypropylene capillary tube heat exchanger is presented. The storage is located in a multi-story office building in Gothenburg, Sweden and is used for daily peak shaving of the building's cooling energy demands. The daily utilizable storage capacity for the installation was determined to be 99kWh, which is 36% of the installed capacity given by the storage manufacturer. The major limiting factor were found to be 60-75% smaller charging rates than what was designed by the manufacturer. Using a mixed integer linear programming model (MILP) to yield optimum scheduling, the storage investment cost limit for a 5 year payback time can be estimated as 9804 SEK (approximate to 921 EUR). These developed key performance indicators can be readily compared against alternative storage technologies and designs in order to select the optimal storage design for equivalent applications. Future work is needed to investigate reasons behind the lower than expected storage capacity.