Lighting Control Systems for Energy Saving and User Acceptance: State-of-the-art and future directions
Abstract: Lighting accounts for one-fifth of global electricity use. In Sweden, energy demand for lighting corresponds to 20% of the total electricity use in office buildings. Lighting retrofit measures are considered to be among the most cost-efficient way to reduce energy use in buildings. In particular, the use of advanced lighting control systems promises energy savings of between 2 and 60%, but system failures and poor user acceptance have been significant limitations so far. This thesis uses literature reviews and field studies to investigate the effect of lighting control systems on energy use and user acceptance. In the first part of the thesis, an extensive literature review on lighting control systems indicates that manually controlled systems are generally more accepted by the users. Systems with high automation and no manual override tend to be deactivated or even sabotaged. Consequently, user behavior plays a fundamental role in ensuring proper function and actual energy savings of the lighting control system. The review also showed that presence and absence detection are often combined under the overarching category ‘occupancy strategies’, although they yield very different energy savings. The review of daylight harvesting systems highlighted critical issues relating to design and commissioning. Two field studies in individual offices were conducted. Absence and presence detection, daylight harvesting and a simple task light were tested in a real-life work environment, where energy use and user acceptance were monitored. The studies showed that the definition ‘occupancy strategies’ is not completely appropriate, since ‘absence’ and ‘presence’ detection yield different energy savings and user acceptance. The second field study showed that daylight harvesting systems could perform well, on condition that careful design and commissioning are performed along with provision of a manual override. However, the field study showed that the use of sensors and microcontrollers raised the energy demand for parasitic power (standby), which might be significant in relation to final energy use, especially with low occupancy rates and high-efficiency light sources. Lighting control systems based on wireless networks and integrated in the building management system are expected to increase during the coming years. This will overcome many of the current issues with advanced lighting control systems, but it will also require additional skills on the part of the designer and installer. In the meantime, occupancy strategies represent a good alternative in energy-efficient lighting retrofit.
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