How to Design a Proper Daylight Control System? An Example of Calibration Under Overcast Sky Conditions

Despite the benefits that lighting control systems provide in terms of energy saving and improving user comfort, these systems are not very spread due to several factors. Furthermore, one of the main challenges to overcome in the configuration of these systems is the adaptation to natural lighting, due to its continuous variations. With this paper it is proposed to give the keys to obtain a simple automatic control system, which gives good results and low cost. To do this, it is proposed to find the existing correlation value between the photosensor signal and the work plane illuminance to calibrate the system under overcast sky conditions. For this, a private office in Naples is considered as a case study. Specifically, three calibration strategies were compared, respectively based on 1) data referred to the entire year, 2) data referred to each month and 3) data depending on sun position. The results obtained show that the best calibration strategy for this case located in Naples and facing south, is considering the position of the sun. This is so because it has been demonstrated that despite being an analysis under overcast sky condition, there is an influence of the incidence of the sun.