Lighting controls increase energy performance
Engineers should look at the specific lighting control requirements in the latest versions of ASHRAE Standard 90.1 and IECC and review some best practices and insights on how incorporating lighting controls influences a building’s energy performance.
High-performance, energy-efficient buildings tend to be the obvious choice in today’s design of commercial buildings, and lighting is a primary target for energy savings. However, not that long ago, energy conservation was not a primary consideration in building design. In response to the energy crisis of the 1970s, the first standard for energy efficiency was established in 1975 and is the standard we still know today as ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings.
The creation of this standard initiated the formation of many energy codes and standards over the next few decades, and in 1998, the International Energy Conservation Code (IECC) was developed. Today, both ASHRAE 90.1 and IECC have become widely adopted as the benchmarks for energy efficiency in buildings. There are numerous other relevant energy codes such as ASHRAE Standard 189, California Title 24, and various state energy codes, as well as building rating systems such as Energy Star, U.S. Green Building Council (USGBC) LEED, International Green Construction Code (IgCC), and the Architecture 2030 Challenge.
For the purposes of this article, the term “energy codes” is used to describe both ASHRAE 90.1 (a standard), and the IECC (a code) as a collective group. To check the status of current energy code adoption across the United States, refer to the U.S. Dept. of Energy Building Energy Codes Program at www.energycodes.gov (see Figure 1).
The primary purpose of the energy codes is to conserve energy in commercial building construction. The codes include requirements for building envelope and HVAC equipment, and devote an entire chapter to lighting. While energy codes may be confusing, their proper application has the potential for significant energy savings.
Lighting power densities
There are two main methods of reducing lighting power consumption within buildings: restricting the input wattage of fixtures and restricting the length of time the fixtures operate. Energy codes address both of these methods; however, this article will only discuss methods of lighting control with the intent to optimize the length of time a fixture is in operation.
This is not meant to diminish the importance of lighting power density in lighting design; it is simply not within the scope of this article. The concepts discussed in this article should be used in tandem with lighting power reduction as a complete method to reduce lighting power consumption.
Automatic space control
One of the fundamental principles of the energy codes is to regulate how lights are turned on and off in a space. Controlling the duration artificial illuminance is energized is one of the most basic methods of conserving energy. The code requirement states that the lights in most areas must be automatically switched off either via schedule-based or occupancy-based shutoff. (Certain exceptions apply to this requirement as well as to the other the requirements discussed in this article; however, a discussion of the exceptions is omitted for the sake of brevity.)
Next, the codes address how the lights are permitted to be turned back on. The latest codes mandate that using sensors that simply switch lights on and off based on passive infrared or ultrasonic technologies is no longer acceptable. The controls are still required to automatically switch the lights off when a space is unoccupied, but now they are not allowed to automatically switch the lights back on. The controls must be set so that the fixtures are either manually turned on, or if automatically switched on, they may only be switched on to not more than 50% power. This can lead to additional ballasts, fixtures, and wiring, so an automatic on design at this reduced power may not be the most economical solution.
Meeting these fundamental requirements may be accomplished in a number of ways, and the designer must first consider the use of the space. Small areas with less predictable schedules or intermittent usage, such as private offices and conference rooms, are good candidates for occupancy-based shutoff. Occupant sensing devices are installed to signal the lighting to turn off when an area becomes unoccupied and are set to automatic off/manual on (referred to as “vacancy sensing”). Controls for larger spaces with regular schedules, such as common areas and open offices, are better suited for a schedule-based shutoff. A relay panel design solution suits this application because it offers flexibility with scheduled automatic shutoff during normal business hours with the option to manually override the controls if an occupant should require lighting beyond the normal schedule.
After applying automatic control strategies, lighting reduction requirements offer additional energy savings by further reducing the lighting power used throughout the day. The codes state that separate controls are required to reduce the lighting power in a reasonably uniform pattern across the space. The lighting reduction requirement is designed to allow occupants to actively reduce the output of the lighting in the space to adjust to their personal comfort level. Several methods of reduction are described in the codes, ranging from separate switching to continuous dimming.
Dimming of fixtures in a space is achieved by adding a dimming ballast or driver to the fixture, and while this option will yield the greatest range in flexibility for lighting reduction, it may drive up the overall cost of the lighting control system. A dual-ballasted or stepped-ballasts approach may reduce the premium for dimming by as much as 85%.