Daylight-linked control systems: a new method to assess their performances

According to a recent Navigant Research report (Market Data: Intelligent Lighting Controls, 2017) revenue from lighting control systems is supposed to grow at 14.3% compound annual growth rate between 2017 and 2026, considering all building types globally. The spread of sophisticate lighting controls is especially expected in tertiary applications and specifically in retail, office and education sectors, due, on one hand, to higher lighting energy costs and, on the other hand, to the necessity of guaranteeing high visual comfort conditions. Indeed, the use of smart lighting systems allows to reduce energy costs, since lights are turned on only when necessary, and to improve visual comfort, tailoring light characteristics to people needs. Control strategies can be classified in three categories depending on the device operating the control. It can be a timer (regulating flux emission depending on a specific scheduling), an occupancy sensor (regulating flux emission depending on occupants’ presence/absence) or a photosensor (regulating flux emission depending on indoor daylight availability). Despite noticeable related achievable energy savings, the use of daylight-linked controls based on photosensors is rather limited if compared with the two other strategies. This is mainly due to difficulties in designing and properly installing them (since many factors affect these systems performances) and to uncertainties connected to achievable energy savings calculation procedures, reducing reliability in their convenience evaluation. So, it is fundamental to experiment methodologies useful to evaluate daylight-linked control systems performances both during design phase -to predict installation usefulness- and during commissioning -to verify installation properness-. Given that, a method is here presented in order to assess the capability of different daylight-linked control systems typologies in integrating daylight. This is based on the calculation of new performance parameters: Daylight Integration Adequacy (DIA), Percentage Light Deficit (LD%), Percentage Intrinsic Light Excess (ILE%) and Percentage Light Waste (LW%). Reported results are a summary of authors’ previous researches. Specifically, illuminance measurements were performed in an office of the Department of Industrial Engineering of the University of Naples. Collected data are referred to the workplane and to a ceiling-mounted luxmeter. Starting from this luxmeter detections and from the observed ratio of the workplane illuminance to the ceiling illuminance, the functioning of different control systems was simulated. Related performances were analyzed by means of the abovementioned parameters. Results were compared and factors mostly affecting control systems operating conditions were highlighted.