Energy-maintenance optimization for retrofitted lighting system incorporating luminous flux degradation to enhance visual comfort

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Retrofitting existing buildings with energy-efficient lighting systems is an effective way to reduce their lighting energy consumption and improve lighting quality. In a lighting system, the illumination level decreases over time owing to the luminous flux degradation of lights. This degradation may cause visual discomfort if proper maintenance is not carried out. Also, energy savings decrease with the degradation of retrofitted lights. Maintenance of lighting devices requires investments for the purchase and installation of new lamps. Therefore, optimum balance is required between maintenance costs and the performance of the lighting system. This study presents an energy-maintenance optimization model, which takes into account the luminous flux degradation. Luminous flux degradation is modeled based on users’ lighting level requirements. Based on the proposed luminous flux degradation model, the energy-maintenance optimization model is formulated to find the optimal number of lamps to be replaced, maintenance schedules, and brightness dimming level, while taking into account users’ lighting level requirements, maintenance budget, and energy savings. An open-plan office is taken as a case study to illustrate the effectiveness of the proposed optimal energy-maintenance plan. It is found that the optimal energy-maintenance plan yields to 31.27 MWh energy savings in 10 years. Compared to the full maintenance, the optimal maintenance plan developed in this study reduces the total maintenance cost by 30%.