Wireless lighting control systems allow users to avoid the cost and complexity of installing new wiring, but how well do they work?
The GSA’s Green Proving Ground program tested advanced lighting controls with wireless networking in two California office buildings and discovered energy savings of 54% when pairing the controls with fluorescent lamps that have dimmable ballasts and 78% when the controls were matched with LED fixtures.
The John E. Moss Federal Building in Sacramento and the Appraisers Building in San Francisco served as the test sites for the control retrofits. All of the fixtures in both sites were programmed into zones, each of which received at least one occupancy sensor. Photosensors were added to zones along the perimeter to enable daylight harvesting. The controls utilized an open standards ZigBee mesh network and a web-based interface, and both also integrated with the automation systems at both buildings.
Savings were heavily dependent on the baseline conditions, GSA found. However, the Appraisers Building, which had a baseline EUI of 2.3 kWh per square foot, noted a savings of 39% in lighting energy with the wireless controls compared to an automatic scheduling baseline. Roughly 22% of that was from the occupancy sensors, 10% from institutional tuning and 7% from daylight harvesting. Buildings with the GSA’s average EUI of 3.25 kWh per square foot, however, would see a total savings of 54% with fluorescents or 78% if an LED retrofit was conducted with the control installation.
The incremental cost of adding wireless advanced controls worked out to roughly $1 per square foot for a payback of three to six years; adding LEDs to that retrofit would add up to about $3 per square foot, meaning a 10-year payback if the electricity rate is 12 cents per kWh. This long payback may deter some potential investors, GSA notes.