DESIGN AND OPTIMIZATION OF PCM-AIR COLD ENERGY STORAGE DEVICE TO BE USED FOR PEAK ELECTRICITY SHAVING

Abstract

Parametric analysis and dimensional optimization study for the melting process of the phase changing material placed in cold energy storage devices have been conducted. Phase changing material, PCM, is used to store the cold energy. A cross-flow tubular PCM-air heat exchanger is used. An electricity peak shaving for a summer day in Antalya for 5 hours (10:00-15:00) is aimed. The cooling load of a room (33 m2) in Antalya is taken as a reference value. A minimum cooling load of 2850 W is supplied throughout 5 hours to maintain the building's comfort temperature. Contrary to the studies handling air velocity constant, it is varied during melting in the present study to satisfy the minimum cooling load. The melting process is analyzed using a numerical model. A computational algorithm is implemented in MATLAB environment. The numerical model is validated for the same conditions and the dimensions with an analytical model presented in the literature. A transient analysis has been employed, and the problem is discretized for the time and space domain. A dimensional optimization algorithm is employed. A parameter “performance ratio/ cooling index”, the ratio of total cooling to fan energy consumption, is defined. Spacing between the tubes giving the maximum performance ratio is sought for aligned and staggered tube bank arrangements using this algorithm. The best performance ratio is obtained at 0.2 m/s initial velocities for both arrangements. In addition, the effect of sizing/arrangement of the tubes, PCM mass, and thermal conductivity of the PCM on the melting characteristics is investigated. As a result of increasing the thermal conductivity from 0.2 W/(m·K) to 0.6 W/(m·K), the performance ratios are raised 4.58 and 3.52 times for aligned and staggered orders, respectively. It is calculated that 10 kg PCM can be saved thanks to enhancing the thermal conductivity of the PCM.