Occupancy sensors reduce energy case

TRW’s Space and Defense Park is an office building campus of more than three million square feet in Redondo Beach, Calif. Jerry Andis, the director of the company’s energy management program when the lighting upgrade program began, knew that there were opportunities to reduce the multimillion dollar lighting energy bill. “We wanted a system that would be flexible to meet our changing needs, that would be reliable in turning the lights on and off, and that would be convenient for our employees,” he said. Those criteria led Andis to occupancy sensors.

TRW conducted a painstaking, 18-month evaluation of options. The first step was a pilot study in which different types of sensors were installed in six offices. The energy savings shown in those offices led TRW to install 550 sensors in two buildings. That test confirmed the forecasts by the company’s energy management team for cost and energy savings. As a result, TRW has retrofitted more than 8,000 offices, labs, conference rooms and work areas with occupancy sensors and continues to install the sensors in new construction.

The sensors have reduced by 50 percent the total number of kilowatt hours used by TRW to light the offices where they are installed, Andis says. The bottom line: TRW is saving more than $1.3 million per year after the installation of the lighting controls. Each sensor saves about $169 per year. Andis reports that the sensors paid for themselves in 1.1 years, a 61 percent return on investment.

Lighting energy savings aren’t the only economic benefit of lighting controls. By reducing the amount of time lights burn, controls also reduce the cooling load of a building. And a reduced cooling load can translate into smaller HVAC equipment in new construction or renovation projects. Having the mechanical engineer rightsize the HVAC system in this way can trim both first costs and operating costs — savings the facility executives should consider in the economic evaluation of lighting controls.