Chillers Operating Strategies of a Thermal Energy Storage System: Case Study of a Gas District Cooling Plant

Chillers could either be operated on continuous basis or only during selected hours of a day to generate required chilled water for the thermal energy storage (TES) system. The operating strategy depends on the design configuration of the system. The strategy was studied for a TES system of a gas district cooling plant in an educational institute. The TES system consists of two absorption chillers and four electric chillers with unit capacity 1250 RT and 325 RT respectively. The system is also equipped with a 10,000 RTh thermal storage tank. The system delivers chilled water at 6oC and receives return water at 12oC. Hourly operating data for three weeks, i.e. one week each in January, April and July 2005, were analysed. Results indicate that for the period under consideration, both the absorption chillers were on full operation during the day and off during the night, with the exception of Saturdays and Sundays. On each Saturday only one absorption chiller was on during the day, while on Sundays none of the absorption chiller was on. However, some changes to the operating patterns of the electric chillers were noted during the three week period. During January, 2005 electric chillers were operated using no fixed pattern. However during April, 2005 the electric chillers were operated continuously during the days of the week, with the exception of Sunday, when it was operated from late morning to late night only. The reason being, the system was required to fulfill higher cooling requirements. In July, 2005 the electric chillers were used in a more organized manner, following the partial storage strategy. Hence the system was adopting both the full load and partial load operating strategies.