Parker, Danny; McIlvaine, Janet; Sherwin, John
In 1995 the Florida Department of Education and the Florida Solar Energy Center jointly sponsored a test of occupancy sensors used to control lighting in a Florida school. Occupancy sensors replace conventional light switches and use passive infrared or ultrasonic sensing to control lighting in classroom and other spaces. The test was intended to demonstrate the performance of such controls in saving energy in Florida educational facilities.
The evaluation was performed at Northwest Elementary School in Pasco County on Florida's west central coast. A before and after monitoring protocol was utilized for the study which saw lighting circuits for 33 classrooms and seven offices sub-metered. Fifteen minute electrical demand data were taken for six months prior to the lighting controls being modified to accomodate occupancy sensors. Recorded data in the baseline period showed that lighting made up approximately 24% of total electrical energy use at the school.
The test building was unusual in that the it contained a modern efficient lighting system with T8 flourescent lamps and electronic ballasts. More importantly, the Pasco County features one of the most aggresive energy management programs of any district school board in the state. Even before installation of the occupancy senors, lighting was effectively controlled by facility staff so as to prevent waste. Given these factors, it was expected that the evaluation in Northwest Elementary would provide insight into the minimum savings that could be expected from the technology in Florida school. A total of 46 occupancy sensors were installed in August, 1995 and then carefully adjusted in terms of location, time delay and sensing sensitivity over the following two weeks. Data were taken in a post retrofit configuration for five months. The analysis of the comparative pre and post retrofit periods showed that the occupancy sensors saved an average of 10% of the pre-retrofit lighting energy (97 kWh/Day) with greater reductions to total energy due to reduced load on the air conditioning system. Most of the savings occurred during the evening hours so that monthly peak electrical demand was little affected.
Including costs of installation and commissioning, the payback of the occupancy sensor retrofit was five years with a 21% simple rate of return from the investment. This performance is considered excellent given the fact that the building already had an efficient lighting system which was responsibly controlled prior to the occupancy sensor installation. The project results indicate that with proper installation and adjustment (which was found to be critically important to user acceptance) occupancy sensor technology will provide economically attractive returns either in new or existing Florida educational facilities.
Florida Solar Energy Center and Floyd, David, "Energy Efficiency Technology Demonstration Project For Florida Educational Facilities: Occupancy Sensors" (1995). FSEC Energy Research Center®. 803.