Daylight-linked Control Systems Research Articles

Testing the use of daylight-linked control systems to address integrative lighting and energy savings in office buildings

Daylight-linked control systems (DLCSs) are used to maintain constant work plane illuminance and save energy. If properly calibrated, they could be used to guarantee circadian requirements fulfilment as well. In this study, the functioning of a closed-loop proportional dimming system is simulated based on on-field measurements. Simulations are performed calibrating the system to achieve different targets: three work plane task illuminances (300 lx, 500 lx, 750 lx) and one melanopic equivalent daylight illuminance (melEDI) value (250 lx) alternatively. Four electric light CCT profiles (stable at 3000 K, 4000 K, and 6500 K, and variable during the day) are considered. Results demonstrate that when the system is calibrated according to work plane illuminance, melEDI values are always fulfilled under clear sky and with overcast sky when task illuminance and CCT are high. When the system is calibrated to meet circadian requirements, the CCT choice is crucial to guarantee work plane illuminance.

Selection of spatial sensitivity curve and installation location of photosensors for daylight-linked control systems in space with dynamic shading devices

Daylight harvesting and daylight-linked control systems (DLCSs) are important building design strategies that maximize daylight usage and save energy. Proper setup of DLCSs, which use photosensor signals to control electric lighting and shading devices, can be challenging. Despite previous efforts to find an optimal layout, locations, and spatial sensitivity curve of photosensors, there are inconsistencies in the findings, and the presence of dynamic shading systems has not been fully addressed. Annual daylight simulations are used to study the impact of the spatial sensitivity curves and installation locations of photosensors for spaces with dynamic shades. This study also provides recommendations for sensor selection, installation, and commissioning. The results show that shading systems cause significant discrepancies in the ceiling-to-task illuminance relationship but restricting the sensor field of view (FOV) can minimize the discrepancies. Cosine-curve photosensors with narrower FOV are capable of predicting task illuminance directly below the sensor and the illuminance of other parts of the space. Light deficit and light waste of the DLCS are strongly affected by ceiling-to-task ratios picked, especially when using photosensors with a low coefficient of determination of ceiling-to-task illuminance. Keeping shades at a low position is recommended when commissioning to avoid a light deficit.

Energy Saving and Life Cycle Analysis of a Daylight-Linked Control System

The main purpose of this work is to examine the environmental impact of a daylight-linked dimming lighting control system integrated in the Lighting Laboratory of Electrical and Electronics Engineering Department, Sakarya University. For this purpose, total annual energy savings and greenhouse gas emission savings is performed in terms of measured annual in operation data and calculated life cycle energy data. The results indicate that the system provides 1,519.55 kWh annual energy savings and spends 365.26 kWh life cycle energy. Assuming that life time of a lighting control system is ten years, annual energy spent by the control system is estimated 36.54 kWh/year. Total annual lighting energy savings, subtraction of estimated annual life cycle energy from measured annual energy savings, are calculated 1,483.01 kWh which is nearly 40% of total annual lighting energy consumption of the test room accordingly. In conclusion, it is established that emissions of the test room are reduced 2.71 tCO2 annually by the lighting control system proposed in this work.

Assessing the lighting systems flexibility for reducing and managing the power peaks in smart grids

The application of “shiftable” or “modulable” load (i.e. washing machine, dishwasher, etc.) in a Smart Grid, can provide energy saving or modify the power flows in the grid, allowing a reduction of the electrical power peak. This paper explores the possibility to modulate the indoor artificial lighting to support this reduction. The study examines the impact of two different measures of power shaving. On the one hand, the change of Correlated Colour Temperature of the light source, and, on the other hand, the dimming of its luminous flux. The possibility to merge the above-mentioned technical solutions is also analyzed. Based on these strategies, several daily schedules of lighting management are defined, and the corresponding energy saving during some critical time slots are assessed. Results show that in all cases, it is possible to achieve a significant reduction of the absorbed power and a consequent increment of energy savings (up to 59%) also in specific time ranges. Furthermore, considering the application of a Daylight-linked control system, it was observed that power regulation associated with the exploitation of the daylight represents itself a way to dynamically reduce the electric loads on the grid.

Automated daylight-linked control systems performance with illuminance sensors for side-lit offices in the Mediterranean area

Abstract Daylight-linked control systems (DLCSs) installation guarantees noticeable benefits, optimizing both energy saving and occupants' visual comfort. These systems performances are influenced by different factors, above all daylight availability. To deepen this issue, daylight illuminance measurements were performed at the work-plane and at the ceiling (corresponding to the position of a typical closed-loop photosensor) in a side-lit office during summer and winter. The office was equipped with two windows: one facing South and the other facing West. For each orientation, starting from measurements, the functioning of different closed-loop DLCSs was modelled. Results underlined that proportional dimming systems guarantee the best performances for each analyzed case, however they demonstrated that, for specific indoor daylight levels and task illuminances, switching systems can be profitable as well. It was underlined that, for specific daylight conditions, integral reset control guarantees performances comparable with those of proportional dimming. However, it was observed that for integral reset and multi-levels stepped systems, the risk that total illuminances (daylight plus electric light) are lower than the prescribed ones is higher than the other analyzed control strategies.

Evaluating performance of daylight-linked building controls during preliminary design

Abstract Thanks to the spread of new light sources and of smart dynamic control systems, automation sector has begun to play a fundamental role in lighting design. In this regard, daylight-linked control systems (DLCSs) represent a particularly interesting research field, since they offer great opportunities both in obtaining energy savings and in improving visual comfort conditions. However, their use is not so spread, because of the difficulties in predicting their functioning during the design process and in evaluating their effective energetic and economic advantages: available technical solutions are so many that design choices can be very hard for specialists. To overcome these obstacles, a precise assessment methodology is needed. Given these premises, the goal of the paper is to show the effectiveness of new performance parameters (Daylight Integration Adequacy, Percentage Intrinsic Light Excess, Percentage Light Waste and Percentage Light Deficit) in order to evaluate DLCs performance and to underline which factors mostly affect their functioning.

Assessment of indoor illuminance and study on best photosensors' position for design and commissioning of Daylight Linked Control systems. A new method based on artificial neural networks

Artificial lighting systems have to ensure appropriate illuminance with high energy efficiency according to best design practice and technical standards. These aims can be tackled, by incorporating a Daylight linked control system. However, the system behaviour is strongly influenced by several factors and, in particular, by the sensors' position. Indeed, very often the illuminance on work-plane is not fully correlated with illuminance measured by the photo-sensor used to control the luminaires. This fact leads to wrong information for the Daylight linked control systems affecting its efficacy. The artificial intelligence of Neural Networks can be exploited to provide a method for finding good relationships between the illuminance on workplane and the one measured in another surface. Artificial Neural Networks are able to process complex data set and to give as output the illuminance in a point. By the use of measured values in an experimental set up, the output of several Artificial Neural Networks related to different sensors placements have been analysed. In this way it was possible to find the position of the photo-sensor associated to the best forecast of the workplane illuminance with a mean square error of 2.20 E−3 and R2 of 0.9583.

Daylight fluctuations effect on the functioning of different daylight-linked control systems

One of the problems preventing daylight-linked controls spread is users' reluctance in accepting them. Continuous electric light oscillations, determined by control systems, can annoy users. This problem is particularly relevant for switching systems and it is strictly dependent on sky conditions: the more variable the weather is, the more frequent the oscillations are. To deepen these issues, irradiance and daylight illuminance measurements were performed in a mock-up office. Percentage daylight fluctuations (PDFs) were calculated. Then, starting from measured data, the functioning of different switching systems (differential switching, switching with switching linked time delay, switching with daylight linked time delay and solar reset switching) was simulated, in order to investigate daylight fluctuations effect on controls performances. Simulations were repeated on varying dead band and time delay, to verify the effectiveness of techniques in reducing daily switching actions. Results demonstrates that when sky is clear, PDFs are generally comprised in the ranges [-5%; 0% [ and [0%; 5% [ both outdoor and indoor; whereas, when weather changes from a sky condition to another, fluctuations can be higher than 50%. Despite the choice of the switching technique is not univocal and its effectiveness strictly depend on specific indoor daylight availability, differential switching associated with a switching linked time delay turns out to be the strategy more adaptable to different cases. Moreover, not always the increment of the dead band extent or time delay corresponds to a reduction of the daily amount of switching actions.

A set of indices to assess the real performance of daylight-linked control systems

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.