The energy and maintenance savings from relamping with LEDs are well known. But incorporating daylight and occupancy sensors into the fixtures themselves raises efficiency to a new level, according to a study by the Lawrence Berkeley National Laboratory (LBNL) for GSA’s Green Proving Ground program.
The LED fixtures were installed at Chicago’s Metcalfe Federal Building and Atlanta’s Peachtree Summit Federal Building. The LEDs integrate advanced lighting control systems (ALC) that can switch, dim and brighten lights in response to daylight and occupancy. The study notes that the initial cost and complexity of implementing such controls has often been prohibitive when the controls have been standalone rather than built into the LED fixture.
Replacing Recessed Fluorescent Fixtures
The applications in the two GSA buildings minimized installation costs by using the wiring of the legacy recessed fluorescent fixtures. Earlier implementations of onboard ALC have required complex programming to assign fixtures to lighting zones and make connections to strategically placed sensors. The ALC-integrated LEDs were programmed and assigned to zones using handheld remote controls. After the supplier programmed a few sample zones, facility staff and contractors were able to program the rest.
“The system was so easy to set up that it literally took us less than an hour to commission all 300 fixtures – and we didn’t need an engineer or program specialist to do it,” says Joshua Westhouse, Building Manager of the Metcalfe building.
Once zones are set up, the fixtures within them communicate with each other wirelessly. Fixtures can operate as part of the zone’s group or as individual units. For example, all lights within a zone turn on to a minimum level if any part of the zone is occupied, but only the lights that sense occupancy brighten to full output. Depending on occupant needs, the maximum light level in a zone can be tuned to low, medium or high. The controls change brightness levels gradually to avoid distracting occupants.
The LEDs replaced fluorescent fixtures in large open-office areas of both federal buildings. LBNL researchers evaluated energy savings, photometric measurements and occupants’ satisfaction.
Savings in Energy and Initial Cost
The surveys showed that occupants were more satisfied with the new lighting’s brightness and illumination of work surfaces. Compared to GSA’s average energy usage intensity (EUI) of 3.25 kWh/square foot/year, the LEDs with integrated ALC provided a savings of 69%. Compared to the national EUI average of 4.1 kWh/square foot/year, the savings were 75%.
Measured against the fluorescent baseline, the wattage reduction from the LED lamps alone accounted for 41% of the GSA’s 69% savings, while the ALC accounted for the remaining 28%. The initial cost of the integrated ALC was lower than that of similar standalone controls – $0.47/square foot for integrated ALC vs. $1/square foot for standalone.
Given the savings, the research estimates an incremental payback between three and four years for renovations and 10 to 14 years for retrofits. Discounted life-cycle cost analysis that considers avoided costs as well as savings creates a more accurate picture of LED cost-effectiveness. Longer-life LED lamps significantly reduce maintenance costs, increasing total system savings by about 25%. For GSA retrofits, the average Savings to Investment Ratio (SIR) is 1.4 (i.e. savings exceeds investment by 40%), assuming the national average utility rate of $.10/kWh and the current estimated cost of $3.29/square foot. For renovations and new construction, the SIR is 4.4 (see graphs).
The GSA’s LED findings, as well as Green Proving Ground findings on other buildings systems, are available at the GSA website.