Improving variable refrigerant flow system operation and energy efficiency: A study of the urban Minoh campus, Osaka, Japan

Variable refrigerant flow (VRF) systems are widely adopted in commercial and institutional buildings; however, their actual performance often diverges from design expectations due to oversizing, low-load operation, and user-driven control behaviors. To clarify these issues and quantify their impact, this study conducts a comprehensive operational analysis of 100 outdoor units and 650 indoor units installed across a large multi-purpose academic building at Osaka University's Minoh Campus. One-year high-resolution operational data were examined to characterize part load ratios (PLRs), COP behavior, refrigerant-cycle conditions, and inefficiencies caused by excessive temperature settings, nighttime unattended operation, and uneven indoor-unit usage patterns. The analysis identified frequent low-load operation and oversized outdoor units as primary causes of performance degradation. After implementing operational energy-saving measures—including optimal temperature settings, reduced nighttime operation, and improved control awareness—the annual VRF energy use decreased by 12.9%. Additionally, a capacity optimization simulation revealed that resizing oversized outdoor units could yield a further 15.9% reduction, emphasizing the need to address both operational and design-level inefficiencies. The study demonstrates that substantial energy savings can be achieved through combined operational improvements and capacity optimization, even in large-scale, diverse-use campus buildings. These findings offer practical insights for enhancing VRF system performance and provide evidence-based guidance for improving energy management in buildings employing distributed air-conditioning systems.