An illuminance ratio prediction method for daylighting control of buildings

Heating, cooling and lighting are the dominant sectors of energy consumption in commercial buildings. Controlling solar radiation through windows will improve the illuminance distribution as well as energy efficiency of buildings. Advanced window systems with motorized shading controlled in conjunction with light dimming constitute a promising approach for improving energy efficiency of buildings. However, the performance of current controlled daylighting systems is neither sufficiently reliable nor accurate, thereby reducing their widespread adoption.; The uncertainty of light dimming control system performance is largely due to prediction of workplane illuminance. This makes the system unreliable and sometimes more complex. To improve the performance of light dimming control systems, the prediction of the workplane illuminance must be considered first. Without thorough understanding of systems, their control may not be achieved efficiently.; A new daylight prediction method, Illuminance Ratio Prediction (IRP) method, is proposed in this thesis for an integrated daylighting control system. The proposed method, which is theoretically developed based on radiosity theory, shows that the illuminance ratio of two arbitrary surfaces in a space in the presence of one initial light source with varying quantity at a fixed location is always constant. The proposed method was experimentally proved. With the IRP method, reliable and accurate predictions of daylighting parameters such as the workplane illuminance, the exterior vertical illuminance and the solar heat gains through the window systems, were obtained as the basis for development of an integrated daylighting control methodology.; The methodology was validated in an outdoor test-room with dimmable electric lighting and a window with built-in motorized blinds. The algorithm was calibrated with a workplane sensor control. Then, an integrated daylighting control system using an interior front wall sensor for prediction was successfully tested. It was found that this system could maintain both the workplane illuminance level and the solar heat gains at the desirable level by simultaneous controls of light dimming and blind tilt angle. With active daylighting control, significant energy savings may be achieved in energy consumption for lighting and cooling. One important asset of the methodology developed is that motorized blinds are optimally tilted so as to admit just enough daylight to satisfy workplane illuminance requirements predicted with IRP method, thus reducing cooling loads due to potential excessive solar gains.