EXPERIMENTAL STUDY ON REGION-CONTROL METHOD FOR A HEAT PUMP-THERMAL STORAGE HEATING SYSTEM

A heat pump-thermal storage system stores thermal energy from a heat pump by using inexpensive electricity that is available at midnight. The utilization of midnight electricity increases with increases in thermal storage usage, and this decreases heat pump efficiency owing to low part load operation. In addition, increased usage of the heat pump enhances energy efficiency of the heat pump system in conjunction with a decrease in midnight electricity utilization. Hence, an optimal control strategy is required to efficiently operate thermal storages and heat pumps during daytime. The region control method assigns a load sharing ratio of heat pump and thermal storage based on variations in heating load. A thermal storage is mostly in charge of the heating load under a low load condition. With respect to medium heating load condition, a heat pump operates efficiently, and this decreases energy consumption and operating cost. In this study, a heat pump and a thermal storage priority method were compared with a region-control method, and an experiment was performed. The results indicated that when compared with the thermal storage priority method, the region-control method had 7% less thermal storage usage but it had 5% less energy consumption as it had a higher PLR of the heat pump. When compared with the heat pump priority method, the region-control method had 32% higher thermal storage usage in addition to 15% lower energy consumption because of optimized heat pump operations. With respect to operating cost, the region-control method corresponded to 6% and 8% lower operation costs when compared with the thermal storage and heat pump priority methods. Thus, it was concluded that the region-control method was more efficient than conventional methods.