Detailed analysis on part load ratio characteristics and cooling energy saving of chiller staging in an office building

Commercial buildings account for significant portions of the total building energy in Korea and thus a variety of research on the chiller operation was carried out thus far. However, most of the researches were carried out on the chiller itself, i.e., the part load ratio characteristics and the corresponding electricity energy consumption patterns were not analyzed in the existing studies. In this study, the part load ratio and the operating characteristics of vapor compression chiller were analyzed within an office building equipped with the conventional variable air volume system. In addition, the energy consumption among different chiller staging schemes was comparatively analyzed. As a result, significant portions of total operating hours, cooling load and energy consumption turned out to be in the part load ratio range of 0 through 50% and thus the energy consumption was significantly affected by the chiller COP (Coefficient of Performance) at low part load conditions, indicating that the chiller operation at the part load is an important factor in commercial buildings. In addition, utilizing sequential chiller staging scheme can save annual cooling energy usage by more than 10.3% compared to operating a single chiller. For further reduction in cooling energy, applying the sequential control chiller staging during the intermediate season and applying the uniform control chiller staging algorithm during the cooling season is considered to be the optimal control algorithm for maximum efficiency of chillers.