Y. Qiao, L. Wang, X. Liu, B. Shen
Oak Ridge National Laboratory,
United States
Keywords: rule-based control, cooling storage, time-of-use, heat pump, load shifting
Summary:
Advanced control strategies can significantly enhance the performance of thermal energy storage (TES) systems, particularly in load shifting. This study focuses on the field testing and simulation of a TES-integrated heat pump (HP) system for cooling storage, aimed at reducing operational costs. The organic phase change material (PCM) with a phase change temperature range of 2–6 K is encapsulated and used in the antifreeze tank to store and release cooling as needed. The TES unit is connected to an air-source heat pump (ASHP) through a plate heat exchanger and hydronic loop in parallel, allowing the ASHP to operate independently of the TES when required. To charge the TES, the outdoor unit of the ASHP functions as a condenser, with the hydronic loop storing the cooling in the TES. For discharging, the hydronic loop transfers the cooling to the indoor air via a water-to-air cooling coil. This research introduces a rule-based control (RBC) strategy for the intelligent charging and discharging of TES, considering time-of-use electricity pricing, weather conditions, and occupant requirements, based on field test results. The performance of the RBC-based TES-HP system is compared to a conventional non-TES-based ASHP system. Additionally, a numerical model of the TES-integrated HP is developed and validated against field test data, and a parametric study is conducted to evaluate the impact of control parameters on load shifting performance. The results demonstrate that the RBC strategy can charge the TES during low electricity price periods, leading to significant savings. Control settings were found to notably influence overall costs. The RBC-based TES-integrated HP system can reduce total electricity costs by 10–20% and peak load costs by up to 70%, while maintaining the indoor air temperature at the setpoint. This study highlights the importance of advanced control strategies in TES-integrated HP systems and the potential for future improvements in control development.