Balancing Cooling and Comfort: Lessons from Fan Coil Units in Estonia

This study examines the performance of fan coil units (FCUs) as active cooling devices during the cooling season across six case settings, located in Estonia. Uncomfortable thermal conditions are known to impair cognitive performance, reducing concentration, memory retention, and reaction speed, whereas thermal comfort enhances productivity. Draught risk was evaluated through air velocity measurements conducted with a thermal comfort measurement kit equipped with low-air-speed probes. Measurements were performed in three open-plan offices, in two control centers, and in one computer classroom. The measured rooms were equipped with ceiling-mounted FCUs - either water-based or multi-split systems. The high-temperature cooling system demonstrated superior performance, maintaining air velocities predominantly below 0.2 m/s. Draught risk and occupant complaints were predictably more pronounced in spaces with high ceilings. In several cases, workstation layouts were modified to avoid cold air jet zones, leading to inefficient spatial utilization. These results reveal deficiencies in the FCU system design and commissioning process, emphasizing the need for proper unit placement and thorough performance verification to ensure occupant comfort and spatial efficiency.