Operation guidelines for daylight dimming control systems in an office with lightshelf configurations

This study examines the system performances of daylight dimming controls under various photosensor conditions in an office space with three lightshelf configurations to propose operation guidelines for the control systems. Using Lightscape, computer simulations were conducted for photosensors positioned at three points with three shielding configurations, and a series of computations procedures were employed. The results indicated that a photosensor should be at least shielded partially and positioned at the center of the ceiling or any point beyond the center to the back wall to ensure optimum system performance of the dimming controls under clear and partly cloudy skies. The dimming control system affected by the photosensor positioned 2 m from the window failed to provide the target illuminance under all the photosensor shielding and sky conditions. No-shielding conditions were inappropriate for most of the cases, because over dimming occurred owing to the excessive light detection at the photosensors. The coefficient of determination between the desktop and the photosensor illuminance due to the daylight varied from 0.8568 to 0.9965 for all cases. The maximum lighting energy saving were 77.5% under a partial shielding condition for a clear sky. The lighting energy savings were not significantly different for the photosensor positions at 5 m and 8 m under clear and partly cloudy skies. Under overcast sky conditions, the dimming control systems operating with partial and full shielding provided the target illuminance but achieved less than 25% energy saving.