Evaluating cost-efficient P.I.R. occupancy sensors: a guide to proper application

Energy engineers and building managers are becoming increasingly aware of the benefits of occupancy sensors. First introduced more than a decade ago for security use (which continues to be a peripheral performance benefit), occupancy sensors today are used to help reduce the mounting costs reflected in the monthly electric bill. For example, they can achieve energy savings of 25 to 50% in virtually any building with only minor modification of the existing lighting system. As lighting can represent up to 30% of the annual electric costs of a commercial building, such energy savings are significant and put money back to where it belongs--the institutional budget. If the local utility unit price of energy is more than eight cents, the payback will typically be less than two years. Occupancy sensors, however, remain application-sensitive devices. Improper positioning and setting may result in performance that fails expectations. In this article, the authors will review how occupancy sensors save energy, then discuss proper application so that installation is effective as well as energy-saving--essential when considering the lighting system's intent, which is to provide a quality environment for people.