Determining Photosensor Conditions of a Daylight Dimming Control System Using Different Double-skin Envelope Configurations

Daylight responsive dimming control systems are analysed in a small office with a double-skin envelope to recommend better control alternatives for achieving target illuminance and better energy savings. Computer simulations are performed for photosensors positioned at three different locations in three different shielding conditions. These are applied in both northwards and southwards facing rooms. Daylight conditions included three sky types at different times of the day and year. Shading device conditions are: a horizontal blind on the external envelope, a combination of a horizontal blind on an external envelope and a retractable shading device on an internal envelope. A partially-shielded condition generally achieved good dimming performance under clear and intermediate cloudy skies. Regardless of position, the unshielded photosensors generally fails to achieve target illuminance, providing excessive dimming levels for all tested daylight conditions. Reasonable lighting energy savings are achieved. The savings were not critically influenced by the photosensor positions, but rather are impacted significantly by the sky conditions. Linear prediction models are studied to determine the relationship between photosensor signals and workplane illuminance according to photosensor conditions. The models are acceptable with low significance levels. The linear correlation is best for the partially-shielded condition, but the correlation is weaker for the fully-shielded photosensor.