VAV fan coil and demand controlled active chilled beam systems energy efficiency and thermal comfort performance comparison in a Japanese office building

In this study, we conducted a comprehensive analysis of indoor thermal condition, indoor air quality and energysaving potentials in a Japanese office building, comparing demand controlled VAV fan coil and active chilled beam (CB) room conditioning systems. The significant difference in these systems is whether or not to recirculate the conditioned air. The comparison was conducted with Osaka climate where cooling dominated over heating needs and higher summer humidity posed additional challenges. A typical Japanese office building was modeled in IDA-ICE for multizone operational performance assessment of studied systems. Also, primary side of heating and cooling system with air to water heat pump chiller was simulated using LCEM-tool ver. 3.01 to analyze HVAC energy consumption. Fan electricity was reduced with the implemented CB over existing fan coil system. These energy savings can be attributed to the difference in supply air volume and FCU installation. Both systems maintained indoor temperature and CO2 concentrations within the same limits, requiring fine-tuning of setpoints. CB operated with slightly higher relative humidity as it is less effective at dehumidifying the air, operating at non-condensing coil temperatures with dew point control. Overall seasonal coefficient of performance (SCOP calculated with PEF) was 1.37 for VAV system and 1.45 for CB system. The findings offer insights for sustainable HVAC systems, enhancing indoor air quality in offices.