Design and Economic Analysis of an Actively Controlled PCM Cold Thermal Energy Storage Demonstrator

Space cooling has seen a faster growth than any other major end-use in the buildings sector and demand could be further amplified if extreme temperatures occur more frequently. Flexible HVAC (Heating, Ventilation and Air Conditioning) systems with active thermal energy storage (TES) offer great potential for demand side management, such as load shifting, peak shaving or increased self-consumption of renewable energies. Utilizing latent heat of phase change materials (PCM) can further increase storage density. However, efficiently charging, discharging or taking advantage of the full storage capacity have been proven difficult so far. In this work, we propose a hydraulic layout to actively charge and discharge a packed-bed PCM TES tank, that conforms to reliability and safety requirements for continuously providing cooling to relevant infrastructure. To evaluate the cost savings potential, a simulation of the charging and discharging process is performed and the truly utilizable storage capacity determined. A MILP (Mixed Integer Linear Programming) model, fed with recorded data and dynamic electricity prices related to the EPEX Spot market, is used to solve the charging-schedule problem and assess the theoretically achievable savings for multiple scenarios. We find that to achieve an amortization time of 10 years by exclusively load-shifting, investment costs would have to drop by at least 57%. However, by combining load shifting with peak shaving and a power-dependent electricity tariff, amortization times of less than 10 years can theoretically be achieved.