An energy-neutrality based evaluation into the effectiveness of occupancy sensors in buildings: An integrated life-cycle study

One of the rapidly emerging trends towards sustainable urbanization are smart cities which consist of smart homes as its building blocks. India is rapidly moving towards becoming a country with 50% of its population (600 million) which would live in the cities by 2030. The rapid urbanization would be a huge challenge in view of the overpopulation, resource shortages and energy crisis; and smart cities (and controls) could be viewed as one strategy to regulate energy consumption. Energy consumed for lighting and ventilation represents approximately 90% of total energy consumed by commercial buildings, especially in the tropical Indian conditions. Occupancy sensors monitor indoor environment and regulate the energy consumption in building integrated systems. While there is evidence of immediate energy saving by the adoption of such measures, one needs to carefully discern the effectiveness of such measures over the life-cycle (energy) of occupancy sensors. Energy neutrality, defined here, assesses the life-cycle energy of an occupancy sensor against the accruing energy saving from the connected luminaire (device/appliance). Preliminary studies have shown that for certain type of luminaires the energy neutrality is quite high to justify use of the sensors itself. Life-cycle application energy integrates the life-cycle energy study associated with a sensor versus the energy saving accruing due to its adoption in the building-integrated system. The increasing evidence of rebound effect, attributed to energy efficiency, has motivated this study to assess effectiveness against efficiency. In this paper design features of these sensors have been studied for their adoption for lighting loads in typical office buildings. The role of designer in designing such smart sensors for energy-neutral smart homes has also been examined through case-studies in the Indian context. The study could provide valuable feed-back to both designers, that of the sensor and of the building (architect), in designing a low-energy sensor and also deciding on whether installation of sensors is effective from an energy neutrality point of view.