| Summary: | 碩士 === 國立臺北科技大學 === 冷凍與低溫科技研究所 === 90 === According to some investigation, the number of cool storage air-conditioning systems accumulated over the years has reached more than 350 sets in Taiwan. The total storage tank capacity has also accumulated above 1 million RTh. It has played a significant role in shifting peak power load due to air-conditioning. Pumps are used in cool storage air-conditioning systems to deliver the chilled water (or brine water) through chillers, storage tanks or heat exchanger (load side). Either in full or partial cooling load situation, the pumps often operate in full flow rate and some pumping power is thus wasted. By a survey and a simple analysis, the power consumption of the pumps of a cool storage system (circulation through the chillers and the storage tanks) ranges between 8%~26%. ASHRAE STANDARD 90.1 suggests that pumps with capacity above 37kW and 300kPa should install variable-speed-drive for energy conservation. This indicates that variable speed drive (e.g. variable frequency drive) has become a main energy conservation measure. The study presents the results of the energy conservation potential when variable speed drive is applied to chiller pumps and ice melting pumps in cool storage systems.
The study focuses on internal melt ice-on-coil cool storage systems. The model of analysis for chiller pumps and ice melting pumps with variable-flow operations are built in this study. The analysis was done using a yearly dynamic cooling load profile to calculate the hourly cooling and water flow rate requirements. A practical case was used for computation of the dynamic cooling load, discharge rate required of the storage tanks, and tanks discharging characteristic. Thus theoretical pump flow rates and pumping power during the discharging of storage capacity can be obtained. Theoretical pumping energy for a year was computed and is good agreement with an actual case if actual operation conditions are considered. It is found that pumping energy saving potential of more than 60% is feasible with variable flow design of pumping systems.
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