Can Hourly-Based Annual Daylighting Simulations Predict Daylight Availability in Dynamic Sky?
For successful daylight harvesting in buildings, daylight availability should be accurately evaluated and predicted. Daylight availability can be evaluated by either point-in-time computer simulations under a predetermined sky condition for a given site’s geographical location or climate based daylighting simulations with standard meteorological datasets. However, predetermined sky condition or hourly climate data might not be able to predict drastic changes of dynamic sky. As daylight harvesting performance depends on daylight availability, it is important to check whether or not there is significant discrepancy between hourly-based daylighting simulations and real time measurements of luminous environment under dynamic sky conditions. Located in San Antonio, a closed office space with south facing windows was selected for both field measurements and computer-based daylighting simulations. Constant monitoring of indoor and outdoor luminous environments were compared to hourly-based daylighting simulation results in order to verify its effectiveness in predicting daylight availability in dynamic sky conditions. Vertical and horizontal illuminance levels were measured to document natural light distribution inside the office every minute for a 40 day period. Collected data shows how quickly and drastically indoor luminous environment has changed under the actual sky conditions, which would greatly impact electric lighting and interior blind controls.