| NZB: DAYLIGHTING |
Commissioning Occupancy Sensors Lighting controls allow buildings to achieve significant savings in well-designed daylighted facilities. However, if these systems are not installed properly, notably occupancy sensors, a portion of these potential savings will be squandered. The solution: commission said sensors.
Barbara HorwitzBennett has been reporting on the architectural industry for the past 15 years. She covers glazing and daylighting for Architectural Products, and in 2011 contributed to an important industry white paper on net-zero buildings.
roven to be highly beneficial, the commissioning process, according to Lawrence Berkeley National Laboratory, is “arguably the single-most cost-effective strategy for reducing energy, costs and greenhouse gas emissions in buildings today.” The process of commissioning, mandated by LEED for certification, and also required by a number of energy codes, ensures that lighting control systems, including occupancy sensors, satisfy design intent and owner requirements.
Best Practices The process really begins with a few best practices architects and installers can employ to ensure that occupancy sensors are properly positioned and set up. For sensors that incorporate a daylighting control component, Jennifer Li, P.E., LEED AP, and an energy engineer at Seventhwave, Madison, Wis., recommends beginning with a study of the sensor’s coverage patterns, as well as the manufacturer’s recommendations for optimal placement to sense motion within a space. The latter step, says Li, ensures that a sensor will not see motion outside of the controlled space. Once installation begins, she adds it’s critical that designers follow up on proper placement, including aiming and selection. Another common issue is leaving insufficient distance between a sensor and an HVAC diffuser, which can result in false occupancy detection. Finally, Li advises a double-check of the setting of timeouts and sensitivities. Regarding the former, Craig DiLouie, LC, CLCP, education director with the Lighting Controls Assn., points out that the majority of commercial building energy codes impose a maximum time delay of 30 minutes. That said, he adds the latest
24 | 03.17 | NET ZERO BUILDINGS
ASHRAE/IES 90.1 reduce that number to 20 minutes. “If using fluorescent, a typical time delay is 10 to 15 minutes, which balances energy savings with the effect frequent switching may have on lamp life,” says DiLouie. LED, on the other hand, allows for even shorter time delays, as the effect of frequent switching is negligible, meaning it’s possible to increase energy savings. As a general rule of thumb, Li’s Seventhwave colleague, Scott Schuetter, P.E., LEED AP BD+C, senior energy engineer, recommends longer delays for spaces that are more frequently occupied, or where the sensor may not see the entire space—for example, open office space with high partitions.
The secret to good daylighting results, in context of substantial energy savings for net zero projects, lies in the art of proper commissioning.