Illuminating advances in wireless lighting controls

Figure 1: Summary of pre- and post-retrofit average workday lighting power density at the Appraisers building and three sites at the Moss building.

The Appraisers Federal Building consisted mostly of open office spaces with some private offices and additional rooms. Occupancy sensors and manual switches were already installed before the study. The GPG study included a LED luminaire retrofit combined with wireless controls, and with one controller per luminaire allowing for individual control.

The Moss Federal Building also consisted mostly of open office spaces with some private offices, corridors, and meeting rooms. Each area already had manual switches 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, usually including four to six luminaires. Photosensors were installed in control locations configured within perimeter daylight areas; wireless occupancy sensors were installed, typically one per control location. In private offices, an occupancy sensor, dimmer-switch, and if the office had a window, a photosensor was installed. The system was then tied to an Internet server enabling facility operators to program and monitor the lighting using a web-based interface.

LBNL researchers studied each site before and after the retrofit, which included site visits, energy measuring, photometric study (i.e. light levels), and occupant satisfaction surveys. To form a baseline, a month of performance data was collected for luminaires in three control zones (one in Appraisers and two in Moss), estimating average lighting power density and annual energy consumption. Various lighting scenarios were then implemented and monitored to identify energy savings resulting from various control scenarios.

The advanced wireless lighting control (Figure 1) resulted in 32 per cent lighting energy savings at the Appraisers Federal Building, and the same for the three sites located in 
the Moss Federal Building.

Shedding light on the key findings
The lowest energy savings (i.e. nine per cent) at one of the Moss sites consisted of 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 per cent level during periods of no occupancy, as opposed to previously being turned off by occupancy sensors. The highest energy savings were 42 and 47 per cent and located at the other two Moss sites; they were 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 per cent, from 0.97 to 0.44 W/sf. Total energy savings, including the wireless controls, increased savings to about 69 per cent.

The LBNL researchers were able to disaggregate the performance of various control scenarios. In one of the Appraisers locations, occupancy sensors were implemented on about one-third of the luminaires. This was found to produce 22 per cent energy savings relative to a basic time-based control strategy, with an additional 10 for institutional tuning and seven for daylight harvesting. Ultimately, advanced wireless controls were estimated to save about 39 per cent lighting energy compared to time-scheduling control.

The researchers concluded implementing advanced wireless control systems can save significant lighting energy. It was noted savings are not guaranteed, as they depend on baseline control conditions (e.g. whether an existing system already has occupancy sensors installed and prevalence of daylight).

Figure 2: Estimated project costs for retrofit and new construction scenarios involving advanced wireless lighting controls.
Image courtesy LBNL

At Appraisers, the LED lighting system with advanced wireless controls reduced average light levels from about 613 to 398 lx (57 to 37 fc), which was found to be satisfactory as it was above the 322 lux (30 fc) deemed appropriate for the tasks performed in the space. The occupant satisfaction surveys found inhabitants perceived the new lighting conditions and control performance favourably, with overall 
comfort increasing.

At Moss, average light levels remained fairly consistent before and after the upgrade. Occupant satisfaction was slightly reduced after the retrofit in terms of perception of comfort, light levels, and control performance. The researchers believed fluorescent lamp failures were the result of not being properly seasoned prior to dimming, coupled with commissioning errors and existing wired occupancy sensors applying legacy zoning onto new workstation and controls layouts. (NEMA Publishes LSD 23-2010, Recommended Practice: Lamp Seasoning for Fluorescent Dimming Systems.) Use of wireless occupancy sensors could have improved the control performance, as the 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—however, if luminaires are replaced, installation labour can be economized. In a new construction scenario, return on investment (ROI) is based on the incremental cost of the new controls over an energy code-compliant solution (Figure 2).

LBNL researchers calculated payback ranging from three to six years. This suggests adding wireless advanced lighting controls to projects is a compelling opportunity in new construction and major renovation.

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