A traditional lighting control design deploys manual switches and simple controls such as load scheduling to control large zones of luminaires. Even when occupancy sensors are installed, these devices are typically assigned to large control zones.
Increasingly stringent commercial building energy codes have made control zoning more granular. Emerging control strategies such as daylight harvesting (daylight-responsive lighting) became recognized based on proven effectiveness, resulting in a layering of strategies. Additionally, smaller control zones generally increase responsiveness, flexibility and energy savings. However, individual luminaire control, with a lighting controller installed in each luminaire, increases equipment costs.
The greatest potential to save energy is with advanced lighting control systems that feature three capabilities. First, all applicable control strategies can be layered in a hierarchy of control zones. Second, zoning can be precisely matched to the application, potentially resulting in a mix of larger zones with zones as small as individual luminaires, which increases responsiveness while allowing personal control of overhead general lighting. Third, these systems provide a central mechanism for calibration, sophisticated programming, measuring and monitoring.
Wireless lighting control systems are now available that are designed to simplify installation while potentially reducing material and labor costs associated with control wiring, making highly granular zoning more cost-effective. Radio-frequency (RF) wireless controls originally gained popularity in the residential market. They entered the commercial market after technological improvements and the development of wireless mesh network standards. As such, RF wireless is a relatively young technology in commercial lighting control, albeit one with significant potential.
The General Services Administration (GSA), the agency responsible for Federal real estate management and products and services procurement support, studied deployment of advanced RF wireless control systems in two Federal buildings. The study, conducted by the Lawrence Berkeley National Laboratory (LBNL) for the agency’s Green Proving Ground (GPG) program, sought to quantify the performance of wireless lighting systems.
Two buildings were selected for installation. One is the 16-story Appraisers Federal Building (San Francisco, CA), the other the 8-story Moss Federal Building (Sacramento, CA).
The Appraisers Federal Building consisted mostly of open office spaces with some private offices and other spaces. Occupancy sensors and manual switches were already installed before the study. The GPG study included an LED luminaire retrofit combined with wireless controls, and with one controller per luminaire allowing individual luminaire control.
The Moss Federal Building also consisted mostly of open office spaces with some private offices, corridors and meeting spaces. Each space already had manual switches and/or occupancy sensors, and in some cases, time scheduling systems. The GPG study saw installation of wireless controls with existing fluorescent luminaires in three locations on two floors, with multiple luminaires assigned to luminaire-based controllers.
At both locations, control software was used to assign luminaires to control zones that typically included four to six luminaires. Photosensors were installed in control zones configured within perimeter daylight zones. Wireless occupancy sensors were installed, typically one per control zone. In private offices, an occupancy sensor, dimmer-switch and, if the office had a window, a photosensor were installed. The system was then tied to an Internet server enabling facility operators to program and monitor the lighting using a web-based interface.
The LBNL researchers studied each site before and after the retrofit, which included site visits, energy measuring, photometric study (light levels and color quality) and occupant satisfaction surveys. A month of performance data was collected for luminaires in three control zones, one in Appraisers and two in Moss, so as to estimate average lighting power density and annual energy consumption. This formed the baseline. Various lighting scenarios were then implemented and monitored to identity energy savings resulting from various control scenarios.
• Advanced wireless lighting control resulted in estimated 32.3% lighting energy savings at the Appraisers Federal Building.
• Advanced wireless lighting control resulted in estimated 32.8% average lighting energy savings at the three sites in the Moss Federal Building.
The lowest energy savings (9%) were at one site at Moss, with savings mostly produced by reducing after-hours operation of the lighting. Energy savings were dampened by programming that kept the luminaires at a dimmed (20%) level during periods of no occupancy, as opposed to previously being turned OFF by occupancy sensors. The highest energy savings were at the other two Moss sites, 42 and 47%, which was produced by a combination of after-hours lighting reduction, institutional tuning and daylight dimming.
At Appraisers, the LED luminaire retrofit reduced lighting power density by 55%, from 0.97W/sq.ft. to 0.44W/sq.ft. Total energy savings, including the wireless controls, increased savings to about 69%.
The LBNL researchers were able to disaggregate the performance of various control scenarios. In one Appraisers location, relative to a basic time-based control strategy, occupancy sensors were found to produce 22% energy savings, with an additional 10% for institutional tuning and 7% for daylight harvesting (noting daylight harvesting was implemented on about a third of the luminaires in this group). In all, advanced wireless controls were estimated to save about 39% lighting energy compared to time-scheduling control.
The researchers concluded, “Overall, this study found that implementing advanced wireless control systems can save significant lighting energy.”
They noted that savings are not guaranteed, being dependent on baseline control conditions, such as whether an existing system already has occupancy sensors installed, and baseline site conditions, such as prevalence of daylight.
At Appraisers, the LED lighting system with advanced wireless controls reduced average light levels from about 57 to 37 footcandles, which was found to be satisfactory as it was above the 30 footcandles deemed appropriate for the tasks performed in the space. The occupant satisfaction surveys found occupants perceived the new lighting conditions and control performance favorably, with overall comfort increasing.
At Moss, average light levels remained fairly consistent before and after the upgrade. Occupant satisfaction, however, was slightly reduced after the retrofit in terms of perception of comfort, light levels and control performance. The researchers believe that fluorescent lamp failures resulting from the lamps not being properly seasoned prior to dimming (see NEMA-LSD-23-2010), coupled with commissioning errors and existing wired occupancy sensors applying legacy zoning onto new workstation and controls layouts, may have influenced these results. Use of wireless occupancy sensors could have improved the control performance, as wireless sensors can be relocated easily without rewiring to better align with new workstation layouts.
In a retrofit situation, the project must carry the entire installed cost of the control system, though if luminaires are replaced, installation labor can be economized. In a new construction scenario, return on investment is based on the incremental cost of the new controls over an energy code-compliant solution. The LBNL researchers concluded, “With paybacks ranging from 3 to 6 years, adding wireless advanced lighting controls to lighting projects is a compelling opportunity in new construction and major renovation.”
Click here to download the LBNL report on advanced wireless lighting controls.