Energy and Buildings 149 (2017) 235–245 Contents lists available at ScienceDirect Energy and Buildings j ourna l ho me page: www.elsevier.com/locate/enbuild A set of indices to assess the real performance of daylight-linked control systems M. Bonomolo ∗ , M. Beccali, V. Lo Brano, G. Zizzo DEIM-Dipartimento dell’Energia dell’Ingegneria dell’informazione e dei Modelli matematici, Università degli Studi di Palermo, Palermo, Italy a r t i c l e i n f o Article history: Received 26 January 2017 Received in revised form 27 April 2017 Accepted 24 May 2017 Available online 27 May 2017 Keywords: Daylight-linked control systems Building automation Lighting design Daylight a b s t r a c t The installation of Building Automation Control Systems (BACs) in general is an effective action to achieve relevant energy savings. Commercial BACs, installed in residential or small offices, often include functions of lighting control, acting as Daylight-Linked Control Systems (DLCSs). Nevertheless, because system performance is strictly dependent on different parameters, BAC’s hardware and software configuration and as well as an inaccurate commissioning do not always allow a perfect execution of the desired tasks; therefore, the system could not work as expected. Moreover, it is well known that energy saving potential is specifically related to the variability of the light environment. Although many methods to assess it are available, these are mainly based on average data, tabular factors, and climate/lighting time series embedded in weather files used in detailed simulations and, in general, they adopt as a benchmark the performance of ideal control systems. In this paper, actual performances of a daylight-linked control system have been evaluated by a set of indices which, in general, can be calculated, after measurement, during the commissioning stage or in periodic monitoring of the system. In particular, these indices take into account the excess and the deficiency of illuminance over time with respect to a target set point that a lighting system should provide and the related energy consumption. The indices have been tested using data measured in a laboratory set up where a commercial daylight-linked control system, working not close to an ideal one, is installed and has been evaluated for different end uses, operating schedules, control strategy (dimming and ON/OFF) and daylight conditions. Finally, useful relations between system performance and environmental conditions have been found. © 2017 Elsevier B.V. All rights reserved. 1. Introduction In the last years, an increasing attention has been focused by researchers, designers and technicians on the use of automated light control systems, which are today widespread components of smart buildings. This kind of system can play a key role in achieving a significant reduction in the electrical consumption for Abbreviations: ALD, artificial lighting demand; BAC, building automation con- trol; DA, daylight autonomy; DF, daylight factor; DFave, average daylight factor; ELEC, electical consumption; Eart , illuminance due to the artificial lighting; E in , indoor illu- minance; Enat , illuminance due to the natural lighting; Eout , outdoor illuminance; Eset , illuminance target value on task area; Etot , illuminance due to the natural and artificial lighting; ERI, energy ratio of illuminance; OAR, over illuminance avoidance ratio; UAR, under illuminance avoidance ratio; UDI, useful daylight illuminance. ∗ Corresponding author. E-mail addresses: marina.bonomolo@deim.unipa.it (M. Bonomolo), marco.beccali@dream.unipa.it (M. Beccali), lobrano@dream.unipa.it (V. Lo Brano), gaetano.zizzo@unipa.it (G. Zizzo). lighting and all of the well-acknowledged benefits received from daylight (e.g. occupant comfort, health, well-being and productiv- ity). It is very common, during the design steps, to build reliable relationships between energy saving and available daylight. This is an important task for designers and architects [1]. Many studies have tried to gain understanding of how to assess the energy sav- ings achievable by installing a lighting control system for lighting that works according to the daylight contribution. Most of these compared the energy consumption with and without a control sys- tem [2], others used simulation software [3–13], others used field tests and monitoring [14–19], others developed algorithms or com- bined more methods [20,21]. Furthermore, many indices have been defined to synthetize this information, taking into account climate and luminous contexts. Reinhart improved the Daylight Autonomy originally proposed by “Association Suisse des Electriciens” [22]. Two modifications of Daylight Autonomy are the “continuous day- light autonomy (DA con )” and the “daylight autonomy max (DA max )”. DA con , as proposed by Roger’s [23] associates partial credit for daylight levels below a user-defined threshold in a linear fashion. http://dx.doi.org/10.1016/j.enbuild.2017.05.065 0378-7788/© 2017 Elsevier B.V. All rights reserved.