Occupancy and Time-Based Lighting Controls in Open Offices
We present analyses of two years lighting data in open office areas, controlled by occupant sensors, time scheduling, or wall switches alone. We compare the energy savings using a before-after analysis of time scheduling and a conservative moving baseline analysis of both occupant sensing and time scheduling. We found that both techniques saved energy effectively when no occupants were present compared with wall switches alone. Time scheduling saved from 0.7 to 6.6% or an average of about 5%. Occupant sensors in similar areas saved from 9.0 to 14.6%, with an average of about 10%. False triggering of occupant sensors (by passersby) that would have caused energy waste was avoided by the presence of wall switches that positively turned lights off. Variations in occupant schedules and habits affected overall lighting energy use and the appropriateness of different control types. Little savings were found during the normal 8am to 5pm workday from either technology in large offices, but significant savings occurred after hours and on weekends. Our findings contrast with previous results for private offices in which only a single occupant is present, strengthening the evidence that different types of office space can be controlled appropriately with different types of control systems. However, small percentage savings in open areas result in larger actual savings due to the large number of fixtures controlled.