How energy codes affect lighting design
- Learn the three parts of a building’s energy-efficient lighting system.
- Understand how to create energy efficiency goals for lighting design.
- Use an example to illustrate how to design energy-efficient lighting in nonresidential buildings.
Electrical engineers and lighting designers tackle many challenges as they strive to create design solutions that enrich the built environment. One leading challenge is energy management of electric lighting in buildings. Electric lighting in buildings is a prime target for reducing energy, as it is the largest end use of electricity in commercial buildings, according to the U.S. Energy Information Administration.
There are many motives for advancing energy reduction of electric lighting in buildings, such as sustainable responsibility and lowering ongoing expenses. All of these goals result in less energy consumed for the same lighting deployed in a building.
Effective lighting energy management involves three essential parts of a building’s overall lighting system:
- Electric lighting.
- Lighting controls.
Building energy codes and standards provide prescriptive or performance requirements for the building’s lighting system with regard to its energy use. Lighting design guidelines, like the Illuminating Engineering Society (IES), “The Lighting Handbook, 10th Edition” provide prescriptive requirements for a building’s lighting system for the quantity (illuminance) in each area; the guidelines are written to inform the designer how to adequately light the space. The engineer needs to ensure that the requirements set forth do not inhibit the quality of the building’s lighting system and its positive influence on the built environment.
While many lighting systems are available to help the engineer comply with energy codes and adequately light the space, only some will accomplish this while also enhancing the quality of the built environment. It is the engineer’s responsibility to evaluate all criteria of the application and then select the lighting system that supports both energy reduction and lighting quality.
The primary challenge for the engineer is to ensure that critical tasks are adequately lit. However, the simplest solution, uniformly lighting the entire space to the critical-task illuminance, does not enhance the quality of the built environment nor does it allow for the most energy-efficient strategy. By defining and confining the multiple critical tasks to their respective areas and providing multiple layers of lighting to ensure that illumination of critical tasks is targeted while not over-lighting adjacent areas, the engineer can achieve a non-uniform, layered lighting layout that maximizes both energy management and lighting quality.
The engineer can achieve an effective energy-management strategy that satisfies energy codes and increases lighting quality by performing the following process:
- Determine applicable code requirements.
- Establish energy-management goals:
a. Illumination targets.
b. Lighting-power density (LPD) limits.
- Develop strategies to meet goals:
a. Non-uniform, layered lighting layout.
b. Evaluate efficacy of luminaires.
- Document methods and results.
The energy challenge
Building energy codes were created in response to the first world energy crisis of 1973. Long lines at gas stations, brownouts, and closing of public buildings created demands for more equitable sharing and distribution of energy supplies. As a result, ASHRAE published Standard 90-1975: Energy Conservation in New Building Design, the first professional consensus standard to address building energy efficiency. Around the same time, new legislation in the form of the Energy Policy and Conservation Act of 1975 and the National Energy Conservation Policy Act of 1978 were enacted, which began to require states to adopt an energy standard for nonresidential buildings in exchange for federal support.
In the early 1970s, there were few if any energy efficiency measures for building construction. By midway through the 1970s, a minority of states had adopted an energy-conservation standard. Beginning in the early 1980s, more than half of the United States had adopted energy-related building requirements. A “lighting power budget” was introduced in 1980, which limited lighting energy. By the end of the decade, most states had adopted some form of energy efficiency requirement for buildings.
ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings (1989 edition) included the first use of LPD as a measure of lighting energy use in a building. The passage of the U.S. Energy Policy Act of 1992 was a milestone in energy code history, effectively making ASHRAE 90.1 the law of the land and requiring all states to enforce an energy code at least as stringent, if not more, than the 1989 edition of ASHRAE Standard 90.1 . In 2000, the first version of the International Energy Conservation Code (IECC) was published. The Energy Policy Act of 2005 further elevated energy efficiency by once again requiring states to adopt a new energy code as stringent as ASHRAE 90.1-2004.
This timeline reveals a shift from an industry with few energy-conservation requirements in the 1970s to one where energy efficiency requirements are affecting every way engineers light a building today. A little more than half of the U.S. is still following a code less stringent than ASHRAE 90.1-2010. This is important to note because, between the 2004 and 2010 code cycles, the energy use of a standard building is expected to be 30% less—a significant jump. The jump in energy efficiency is quite large in comparison to the early history of energy codes. In just this past decade, the industry has seen commercial-building energy codes’ efficiency requirements increase by 45%. Contrast this to the 14% improvement over the previous 25 years.
The most current model code for commercial construction calls for energy efficiency levels approximately 37% above those required by the same code 10 years ago. Current policy discussions reveal a similar trend moving forward. A trend toward more rigorous code requirements, more performance-based requirements, more enforcement and auditing, and more post-occupancy building energy performance reporting.
Throughout all of these seismic shifts in the rules governing design and construction, there is a big question: What can engineers do to stay on top of energy code requirements?
Applicable code requirements
The best way to combat these challenges is to develop a process that identifies the obstacles (energy code requirements), creates LPD targets, develops lighting strategies to meet the targets, and establishes periodic milestones to verify that objectives are being met. By using a process like this, the engineer will not be surprised by code requirements. By following the formulas indicated, the design process changes from reactive to proactive.
The first step in solving any problem is to first define it. This means understanding what energy requirements apply to a specific project. To determine this, perform a code search in the project jurisdiction. Go to the state agency that oversees building construction or visit www.energycodes.gov to determine which code the project falls under. Read the code text to understand the version of ASHRAE 90.1 or IECC that the state code references. Then go to the local municipality and see what they reference. The engineer also needs to check when the next code version may go into effect and reference it against the planned timeline to apply for a permit for the project. Large multiyear projects may start design under an earlier version of the code but end up being submitted under a later version because the authority having jurisdiction (AHJ) has adopted more stringent requirements in the meantime.
This applies to all codes, not just to energy codes. The engineer also should check the actual laws written to see if any other requirements apply to their project. Many small communities have harsh, restrictive, or vague requirements for light trespass. These are found in nuisance articles, not in the energy section of the code. There also may be requirements for security lighting in another section of the code.
It is important to determine under whose jurisdiction the project falls. Not every project is held to the local or state code where the building is physically located. Federal facilities do not follow state or local codes; they have their own requirements that can vary by agency or department. State institutions, like public schools, do not have to follow local municipality codes. Next, look at what other requirements may be in effect. Is the project pursuing U.S. Green Building Council LEED certification or other client goals? Is the AIA 2030 Commitment a driver on this project? All of these have various LPD requirements.
At the end of this endeavor, the engineer will have a list of energy requirements, usually summarized as LPD limits. Review them and determine an optimal project LPD target to comply with all of them. While the state/local energy code is a prior edition, an optional requirement like LEED may include more stringent requirements or vice versa. The engineer may be able to make a choice between ASHRAE and IECC, sometimes one is simpler or allows more exceptions than the other. Sometimes, more than one energy code, standard, or requirement may apply to a project. ASHRAE 90.1 is generally more stringent with overall LPD limits than IECC, but also offers several exemptions.
There are many scenarios where other requirements besides the lighting portion of the energy code impact the application of electric lighting. Lighting energy reduction may be required to meet overall energy-reduction requirements of LEED or other voluntary objectives. If mechanical energy improvements or façade improvements are prohibitive, then it may fall to the engineer to earn those energy LEED points. This could take the form of a lower LPD or the use of daylighting beyond energy code-required areas.
The energy code requirements, as well as any additional objectives or standards, must be implemented consistently across the whole project. While it may be beneficial for the lighting designer to select IECC compliance and the mechanical engineer to pick ASHRAE to follow, this is generally not allowed. The design team must decide the project’s energy goals, whether required or optional, as a single project and not as individual disciplines.
Establish energy-management goals
After information gathering, the next crucial step is establishing an LPD target. This target may be in response to a prescriptive requirement, such as the LPD requirements in IECC or ASHRAE 90.1, or a performance requirement from an optional standard like the energy-optimization credits available in LEED. LPD is calculated as watts per area and is the measure of the total input power to a building’s or space’s lighting system divided by the area of that building or space. LPD limits form the backbone of all current building energy codes. Typically, the energy code sets a maximum value for the LPD in a building or a space.
These LPD limits continue to be developed by ASHRAE in conjunction with the Illuminating Engineering Society (IES). They are calculated using generic space and building-type models using currently available luminaires, ideal light-loss factors, IES illumination recommendations, and professional consensus from a committee of electrical engineers and lighting designers. This means IES-recommended illumination levels are possible while still meeting energy code LPD limits. Quality lighting in the built environment can still be accommodated with the LPD requirements being developed by ASHRAE/IES.
Building energy codes typically include a building area method as well as a separate space-by-space method for determining the LPD allowance the engineer can work with. While the building area method is relatively simpler and more straightforward than the space-by-space method, it has an overall lower limit. Engineers may also find themselves handcuffed by the LPD limit for the primary function of the project in the building area method, which does not take into account other secondary functions that may warrant a higher LPD limit. An LPD target for the whole building is a good place to start.
However, to maximize the lighting allowance engineers can work with, it is valuable to determine the LPD targets for individual spaces at the same time you develop illumination levels. This allows the engineer to determine which areas need higher-impact lighting to enhance the design, which will warrant higher-output lighting systems to maintain an overall lighting quality. It also allows the engineer to balance the project’s lighting budget and determine where there is potential to be more aggressive in conserving energy in the building, in order to offset those areas that require more light to maintain the quality of the built environment.
Energy codes restrict LPD measures in buildings to the point where only energy-efficient lighting systems can be viable choices to meet or exceed these requirements. While a variety of viable lighting systems may be possible, only some can meet or exceed the energy code requirements without inhibiting the quality of the building environment for building occupants.
Develop strategies to meet goals
Lighting energy management can be achieved through proper evaluation of appropriate luminaire sources and associated layouts to achieve an energy-efficient lighting design that does not sacrifice lighting quality.
Proper layout of energy-efficient luminaires is required to ensure a quality, energy-efficient lighting system in a space. It would be simpler to identify the most critical task in a space, correlate the appropriate illumination level, and prescribe it over the entire space or building. This would result in a uniform layout of the lighting system throughout the space, even though the critical task may occur infrequently or in a limited area. Spaces outside the defined area of the critical task would be over-lit and result in a less energy-efficient design.
It is important to understand the purpose of the room (what activities will be performed) and identify which surfaces are lighting target planes. Rather than generally lighting noncritical surfaces, designers can employ strategies to intentionally place light where light needs to be to light only the area where the activity is taking place. The layout should follow the identification of specific tasks and task areas. A multilayered, non-uniform approach is usually a wise choice. This would include identifying the multiple tasks in the space and the areas to which they are limited.
The engineer should begin to lay out the lighting by determining which areas require specific tasks, which areas are points of interest within the space, and which areas require general illumination. Once defined, the specifier can tailor specific lighting techniques and fixtures to specific tasks and spaces. This includes localizing the task lighting to the defined task area and reducing the overall ambient lighting in the areas where the critical task is not present. The pinnacle example of this approach is the use of desk lamps in an open-office scenario, allowing the lighting engineer or designer to reduce the ambient lighting in the overall space, thus reducing the energy consumed.
Low-energy lighting systems require energy-efficient luminaires. However, the highest-efficacy luminaire is not always the correct choice. Efficacy is the measurement of energy input per work performed output. In luminaires, it is expressed as the output lumens divided by the input power of a luminaire. While these metrics allow you to pick the most energy-efficient sources, it is important to remember that luminaire efficacy is only one consideration of a lighting product. How the luminaire distributes light and in what quantity are just as important.
It is important for engineers to evaluate luminaires based on a variety of other factors when deciding between fixtures. These other factors, such as luminaire glare control, color temperature, dimming controls and/or presets, and luminosity control, may rule out specific sources due to lighting-quality considerations. Oftentimes, you are purchasing extra lumens and watts that are more than the application requires. Over-lighting a space erases any benefits from higher-efficacy luminaires. Be aware of luminaires that boast higher efficiencies at the expense of a lack of glare control.
Complying with energy codes is just one of the many challenges that lighting engineers face. It also is important to ensure that the lighting quality of the built environment is not sacrificed when designing to reduce energy. Energy codes were written to allow current lighting techniques and methods to succeed. Ensuring success requires more ingenuity than taking the illumination requirements of the critical task in the space and applying them over the entire area with a one-size-fits-all solution.
By selectively applying illumination requirements to discreet task surfaces and areas, the engineer can apply lighting (and its associated energy input) in areas with the highest needs and reduce it in the balance of the building. By evaluating the efficacy of lighting systems, not just the individual luminaire, and choosing quality light fixtures with chromatic and glare control, the engineer can ensure that lighting quality is upheld while still meeting energy code requirements.
By establishing a process that allows for the identification of energy code requirements, selecting LPD limits that comply with these codes, and applying quality lighting strategies, the engineer can ensure a code-compliant design that also enhances the built-environment experience for building occupants and visitors.
Michael Brinkman is an associate and electrical engineer with CannonDesign where he concentrates on solving client challenges for health care, mission critical, and science and technology facilities. Owen Dalton is a lighting designer and electrical engineer with CannonDesign, and is a junior associate of the International Association of Lighting Designers. He focuses on developing lighting and control systems for the built environment .