Commercial Rental Office Building with Developed Convection and Radiant Air Conditioning Systems for Enhanced Comfort and Energy Efficiency

This paper presents an environmentally conscious commercial rental office building in Tokyo featuring a unique architectural design with stairwells integrated into the façade. These stairwells contribute to year-round energy savings in air conditioning by serving multiple functions: acting as natural ventilation shafts through the chimney effect during intermediate seasons, as a double-skin façade in summer, and as sunrooms in winter. Two energy-efficient air conditioning systems—one convection-based and one radiant—were developed and installed on identically designed floors, allowing for direct comparison in terms of energy performance and occupant comfort. Both systems maintain a standard ceiling height of 2800 mm within a reduced overall floor height of 3450 mm (compared to the typical 4000 mm), enabling the addition of an extra floor and expanding the rentable area within local height limits. The convection system uses variable airflow and exploits the Coanda effect to distribute air evenly without ductwork, reducing fan power consumption by 83%. The radiant system employs variable temperature and water flow control to optimize free cooling, even at outdoor temperatures near 30°C. This system achieved a coefficient of performance (COP) of 8.1 when using high-temperature chilled water.