Improving visual comfort and energy efficiency in a classroom : A comparative approach of evaluating a lighting design technique and a sensor positioning method

Sammanfattning: The reduction of energy demand and increased energy efficiency is believed to play a major role in tackling the global climate change. Artificial lighting systems in commercial buildings accounts for a substantial proportion of the total energy consumption. Studies shows that significant energy savings can be achieved by improving the energy efficiency with the application of control systems and daylight sensors. However, this may not come to the expense of impaired visual comfort. This study contains a comparative analysis of methods to improve the visual comfort, optimise light sensor placement for proper performance and estimate the potential energy savings for a classroom located in Umeå, Sweden. The term visual comfort and corresponding photometric properties has been evaluated in regards to international standards and recommendations. The lumen method, a lighting design technique, showed promising accuracy in determining a more optimal lighting design, this was confirmed by using the lighting simulation software Dialux evo. The results obtained by the simulation software showed improved visual comfort in terms of illuminance-based metrics that fulfilled the international requirements EN12464-1.  A sensor positioning method denoted as "Point-by-point" has been evaluated for two different lighting designs. The current lighting design is based on the existing lighting arrangement in the classroom, denoted as "current design". The other lighting design is based on improved positioning attained by the lumen method, denoted "Test design 2". The point-by-point method showed considerate accuracy in comparison to reference values obtained by simulations, however the credibility of the method is dependent on the lighting design. The average deviation for the current design were determined to be 23.7 lx (15.16 \%), whilst the improved Test design 2 attained an lower average deviation of 8.3 lx (9.20 \%). Lighting characteristics of the luminaries also has an impact on the credibility of this method, as uniform lighting proves to be more suitable than non-uniform lighting.  The integration of daylight data in the simulations showed different optimal position for light sensors due to the natural changes in illuminance. Thus, the positions with the most established linear relationships between the light levels on the workplane and ceiling throughout the year were consider to be the most suitable. The point-by-point method for Test design 2 acquired an average deviation of 13.1 lx (16.40 \%) in comparison to the daylight simulations. The results showcased that this method may be applied in similar studies in the future. The daylight simulations indicated significant energy savings throughout the lifetime of the lamp. The most substantial savings were obtained in the month of May during the first year (63.4 \%). This study demonstrates that daylight harvesting is beneficial despite the latitude of the location with proper dimensioning of the fluorescent lighting system.