Electrical Association

The Future in Energy Efficiency - Daylight Harvesting

Written by Scott Rieger, Dunham Engineering

Lighting systems consume 13% of direct energy use in US buildings. Reductions in lighting loads save building owners money over the life of the building and reduce the need to build new and costly power plants. Daylight harvesting coupled with a lighting control system provides an economical means to reduce lighting load in buildings.

Daylight harvesting, or using natural daylight to illuminate spaces, can be tapped as an effective lighting source by adding a photocell in the space you wish to save energy. The photocell is connected either through a lighting control system (LCS) or directly to the fixtures you wish to control. When the lighting level in the space exceeds a predetermined footcandle level, the connected fixtures automatic decrease their lumen output in either a stepped or dimming method. This reduced lumen output maintains the necessary lighting levels while reducing the power consumption of the lighting system, and saving the owner money.

Using an LCS that incorporates occupancy sensors, building-wide lighting sweeps, and local override switches also reduce building lighting loads by turning off, or decreasing light output, of fixtures in areas that are not occupied. This system also turns off all non-life safety fixtures in the building during non-business hours with the capability to turn on areas of fixtures by local override switches for off-business hour use.

Both of these systems are incorporated at the Dunham designed, Great River Energy building in Maple Grove, MN. Over the past year, this facility has seen a 50% reduction in lighting energy use over a similar building that did not use daylight harvesting and an LCS. In addition to the reduction in lighting energy usage, the owner recognizes the additional benefit of less heat generated by the lighting fixtures, that requires additional HVAC cooling capacity. Although these systems are not required by LEED, they did add to the energy performance credits that enables Great River Energy to achieve the first LEED Platinum rated building in Minnesota.

By utilizing daylight harvesting and lighting control systems, new and existing buildings can lower their energy usage, save money, and have a smaller impact on their environment.

From an article by Scott Rieger, Dunham Engineering, 612-465-7550, www.dunhameng.com.