Energy codes and lighting design
Engineers have many resources when designing energy-efficient lighting in nonresidential buildings. Lighting designers do not have to sacrifice quality or reduce lighting levels just to meet energy codes.
When I first started my electrical design career 20 years ago, a lighting design with a lighting power density (LPD) of 3.0 W/sq ft or higher was common and a design of 2.0 W/sq ft was considered “efficient.” Today, lighting power densities that high would never be accepted; 1.0 W/sq ft and lower is typical in most building design applications. That’s a 66% energy use reduction compared to systems installed 20 years ago. Few other design sectors can claim such a dramatic improvement in efficiency in that timeframe.
Over the past 20 years, not only have lighting technologies, lamp sources, and controls improved considerably, but energy codes and green building standards have also driven what we consider to be efficient. We no longer simply lay out 2 x 4-ft, 4-lamp troffers on an 8 x 10-ft grid spacing. Lighting designers, architects, and engineers work together to balance aesthetics, lighting quality, and energy for a better total lighting solution that performs well and complies with energy codes. We do not have to sacrifice the quality of lighting designs or reduce lighting levels just to meet energy codes.
Lighting as an energy reduction target
Buildings use a lot of energy. And a lot of that energy is used for artificial lighting. According to the U.S. Energy Information Administration, 21% of the total energy used in commercial buildings and 38% of all electricity used in commercial buildings is used for artificial lighting (see Figure 1).
In the “original” articficial lighting source developed by Thomas Edison more than 100 years ago, incandescent, visible light was merely a by-product. Incandescent lamps produce light by passing an electrical current through a filament of tungsten metal until it gets so hot it glows. Incadescent sources are essentially resistive heaters with 10% of the input energy producing visible light and 90% of the energy producing heat. Modern lighting sources such as fluorescent and LED are much more energy efficient but still produce heat as a by-product, which has to be removed from the building by adding more cooling capacity to the building’s HVAC system. For every 100 W of lighting that is NOT put into a building, approximately 50 W of cooling energy is saved (depending on the region), making energy-efficient lighting a very attractive target for overall building energy reduction.
Lighting and energy codes
Lighting is a primary component of a commercial building’s electrical system. In the United States, there are a number of energy codes and sustainability standards that help drive overall building energy performance including lighting efficiency.
Each of these codes and standards has its own goals, focus areas, and applications. It can be hard to keep them all straight. Table 1 summarizes various building performance standards and compares their lighting energy requirements for typical hospital/inpatient healthcare, commercial office, and school/university educational buildings.
ASHRAE Standard 90.1 is generally considered the industry accepted baseline standard for building energy performance and is incorporated by reference or otherwise integrated into most energy codes and green building standards. ASHRAE Standard 90.1 addresses lighting energy in two ways:
- Power consumption of lighting is addressed by setting limits on lighting power density (LPD), measured in W/sq ft, based on the specific use of the space.
- Mandates the use of lighting controls to shut off lighting automatically when it is not needed.