Good Design Key to Savings with Occupancy Sensor Controlled LED Systems

Occupancy sensor controlled LED lighting — if done correctly — can enhance savings from an already efficient lighting system as much as an additional 76 percent, after those gained by the initial conversion to LED, according to a U.S. Department of Energy report.

The DOE Gateway Solid-State Lighting Technology Demonstration Program, which evaluates LED products in real-world applications, reviewed motion detection systems at two parking structures and two parking lots. It found a broad range of outcomes (see table) and several issues that affected savings, including product design deficiencies. In some cases, these problems stemmed from inexperience deploying occupancy sensors; in one case the products weren’t designed to sustain exposure to the environment, DOE reports.

Using technology that is not adapted to an individual site can also bring additional energy savings down to virtually nothing, according to the study. Problems here include inadequate or incorrect sensor coverage.

Additionally, widely varying time delay settings between sensors at a single site, and low power settings producing more light than needed during periods of non-activity made occupancy sensor systems less efficient. Overlapping controls over the same lighting system also cut savings.

In one of the report’s case studies, DOE reviewed an underground parking garage in Washington, DC. The project replaced 19 ceiling-mounted 100 W (129.5 W including ballast) HPS fixtures with LED lighting.

The parking garage, located under an office building, is lighted 24 hours per day, 365 days per year; it sees little traffic at nights, weekends and holiday. Most of the spaces are assigned, which means drivers don’t spend much time searching for parking. DOE says the parking garage’s consistent schedule makes is an ideal facility to use motion detectors.

The study found energy savings relative to the original HPS baseline was 74 percent when the sensors’ time delay was set at 10 minutes. It increase to 88 percent at the 2.5-minute setting. DOE says is the initial 10-minute LED setting is used as the baseline (instead of the HPS, yielding a projected 134 kWh/yr per fixture at 2.5 minutes versus 293 kWh/yr per fixture at 10 minutes), the increase in savings from adjusting the occupancy sensor delay is 54 percent.

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