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%.
The use of natural daylighting compares favorably to most artificial lighting systems, and the codes are written to take advantage of daylight as a supplemental lighting source. In spaces with plenty of daylight, this strategy is inherently one of the best ways to reduce lighting energy consumption by controlling the amount of time the fixtures are on during occupied hours. The energy codes define various “daylight zones” based on side- or top-lighted areas and require that these zones are separately controlled.
The daylighting zone control requirements are relatively new to both codes, so it is important for the designer to understand the building envelope and zoning requirements to design the correct control strategy. ASHRAE 90.1-2013 defines the zones based on the total wattage installed, whereas IECC-2012 defines the zones based on square footage and distance from the daylight fenestration. The codes also differ on their method of control. IECC-2012 allows the daylighting controls to be either manual or automatic, but ASHRAE 90.1-2013 requires all daylight controls be automatic.
Acceptable automatic methods are continuous dimming, or stepped dimming using multi-level switching and daylight-sensing controls. As previously discussed, dimming fixtures tends to add initial costs; however, with some facilities seeing an average of 46% energy savings when installing daylight harvesting systems, the return on investment is relatively quick (Energy savings in schools, 2011). A continuous dimming system includes indoor photo sensors where, as the daylight contribution increases in a space, the lights automatically dim to preset levels. This provides gradual lighting adjustments without lowering the lighting quality or levels in the space. Zoning the light fixtures based on their proximity to the window or skylight allows the system to properly adjust the artificial light in response to daylight.
If the project includes exterior lighting, additional requirements are outlined in the codes. The exterior fixtures must automatically turn off based on daylight, and any decorative façade and landscape lighting must be automatically shut off between midnight and 6 a.m. (security lighting is exempt from this requirement). The exterior lighting must also be controlled by a combination of photo sensor and time switch. The basic components of an exterior control system will easily interface with whatever control strategy is applied on the interior of the building for a total building lighting control solution.
Specialty and parking garage controls
Once the above standards are met, the energy codes have more specific requirements for specialty areas such as display/accent lighting, case lighting, and task lighting. These sections remain relatively unchanged from previous versions of the code and require separate control devices for specialty lighting. However, in 2010, ASHRAE 90.1 added a new section dedicated to parking garage control, and in 2013 it enhanced the requirements even further. Previously, requirements for control of parking garage fixtures were not mandated, but now ASHRAE 90.1-2013 requires automatic shutoff in garages based on both occupancy and exposure to natural daylight.
The occupant control must be by one or more devices that automatically reduce power of each fixture by a minimum of 30% when no activity is detected within a zone. A basic solution to the requirement is to provide fixtures with onboard occupant sensors. The onboard sensor signals the fixture to reduce the light output to a preset level. The designer must be cognizant when incorporating such a system, however, to not jeopardize the safety of the garage occupants. ASHRAE 90.1-2013 defines the zone as not more than 3,600 sq ft, so the controls must be triggered far enough in advance so that a car or pedestrian is not entering a dark area before the fixtures are triggered to react.
The code also mandates that additional controls are required to automatically reduce lighting levels of fixtures located with 20 ft of a perimeter opening exposed to daylight. Similar to the indoor application of daylight control, garage daylight sensors must be installed to reduce the light output in response to daylight.
Total building lighting control solution
With a better understanding of how to manage the multiple individual components of the energy code requirements, let’s discuss a total building lighting control system that integrates all of the code required controls into a single system. A full networked
lighting control system is a digital architecture that integrates occupancy-, schedule-, and daylight-based controls into one networked system (see Figure 2). The network control system includes addressable light fixtures, switches, occupancy/vacancy sensors, relay panels/time switches, and photosensors, and when implemented in a facility, it not only meets the current energy code requirements, it also reduces energy consumption and enhances occupant convenience. The system provides the ability to modify any number of parameters such as adjusting time delays in specific occupancy sensors, recalibrating setpoints for daylight controls, and adjusting maximum power consumption on any device in the network from a single location. As the system is calibrated to more accurately react to occupant schedules and the presence of natural light, the overall building lighting power consumption may reduce significantly.
The ultimate goal is to provide not only a code-compliant design, but also a high-performing, energy-efficient building. Fully understanding the detailed requirements of the codes (and the differences between them) will lead the designer down the correct path. Refer to Table 1 as a quick reference guide to the different requirements discussed in this article. As the codes continue to change, so will the available lighting and control products.
A full building lighting control solution may very well become a standard design practice in the near future. The actual energy savings will depend on a multitude of factors such as occupant behavior, building type, site orientation, device settings, and level of commissioning, and the initial upfront cost may sound daunting (anywhere between $1 to $2 per sq ft). However, the realized energy consumption savings average as much as 40%, making the investment well worth the effort.
Danna Jensen has 14 years of experience at ccrd in Dallas, where she became associate principal in 2012. Most of her work consists of designing electrical distribution for hospitals. She also designs electrical systems for office and retail facilities. She is the project manager for major hospital projects, which includes knowledge of all mechanical, electrical, plumbing (MEP), and fire protection systems, as well as commissioning. Jensen was a 2009 Consulting-Specifying Engineer 40 Under 40 winner and is a member of the Consulting-Specifying Engineer editorial advisory board. Jason Jullie has 10 years of experience with ccrd in Dallas as an electrical engineer and associate. He works mainly in the health care field designing electrical distribution systems. He is a 2014 Consulting-Specifying Engineer 40 Under 40 winner.
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