Designing an energy-efficient lighting system
Understanding codes, controls and commissioning are key to an effective lighting design for a new or existing building
- Establish project–specific codes and standards parameters for compliance with regulations adopted by the jurisdiction.
- Select lighting control strategies in compliance with code and the owner’s project requirements, with coordination with the architectural programming of the spaces.
- Determine the commissioning requirement for the energy efficient lighting system.
The foundation of a good lighting design is establishing an appropriate energy code compliance path early in design. Two energy codes, the International Energy Conservation Code and ASHRAE 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings, should be compared and reviewed against the project requirements. These model codes may be adopted by jurisdictions with amendments that must be reviewed together to establish the codes the project must comply with.
The key differences between IECC and ASHRAE 90.1 lie in the requirements for the architectural design, mechanical design, lighting fixture selection and lighting control design (see Table 1). The code selection should be combinative effort of the design team as it relates to the project budget, design and future goals for the building.
Pending the overall analysis, an appropriate energy code must be selected. Each individual energy code provides prescriptive lighting controls and lighting power density requirements for the project. Lighting control strategies include the use of daylight responsive control systems, occupancy sensing and scheduling, lighting reduction (dimming/bi-level switching) and astronomical time clock scheduling.
Furthermore, if the project is seeking U.S. Green Building Council LEED accreditation, mandatory requirements of ASHRAE 90.1 must be provided and the requirements tracked throughout the design process. These parameters should be used to design the energy–efficient lighting control system. .
Once an appropriate energy code is determined, the lighting design should be geared toward providing adequate foot-candles for each space within the project. The foot-candle requirements for each space can be established through a step-by-step method.
First, establish the minimal levels required for egress by reviewing amended model codes such as the International Building Code, NFPA 101: Life Safety Code and NFPA 70: National Electrical Code. Next, review the program specific publications for project specific foot-candle requirements/recommendations.
For example, educational projects would use campus standard manuals while hospital projects might reference Facility Guidelines Institute Guidelines for Design and Construction documents, health care equipment manufacturer requirements or other adopted standards.
It is essential to review program specific publication requirements with owners before construction. This review process will allow the owner to take exception to certain requirements/recommendations that are deemed unreasonable for the project. The last resource in assigning project foot-candles is the use of the Illuminating Engineering Society Lighting Handbook, which provides industry standard foot-candle values for nearly all spaces. The IES Lighting Handbook provides horizonal and vertical foot-candle values for each space type in a building based on the functionality and age group of the space. It is the designer’s responsibility to assess the IES recommendations and select a suitable foot-candle value.
Once the project parameters are established, the design of the energy-efficient lighting system — composed of a luminaire layout and lighting control devices — should commence with the review of the architectural programming of each space. The layout of each space will instruct the designer to recommend certain energy–efficient lighting fixtures and control systems that fit the profile of the project. It is important to dissect the different layers of architectural programming in a project by focusing on each individual room, then by gradually expanding the view to capture connecting spaces, floors and the site to understand the architect’s and owner’s intentions.
In addition to specific architectural programming, each area of the building will feature unique traits that characterize that space relative to those in the rest of the building. For example, each space will contain different natural daylight, interior wall color, ceiling types and furniture layout. Having developed a good understanding of the architectural programming and codes governing the space, the designer should select appropriate energy–efficient lighting fixtures.
Thanks to the advancements in LED lighting, meeting the wattage requirements for each project is easily attainable. The lighting design should meet the energy allowance, outlined in the IECC or ASHRAE 90.1, while delivering the correct foot-candles, highlighting the architectural features of the space and containing the appropriate controllability features.
The lighting designer should develop a typical lighting fixture layout, based on the selected lighting fixtures, for each space type in the project for internal review by design consultant, owner and commissioning professional. Once the typical layout is approved, the designer can repeat the layout throughout the project for consistency. This approach will ensure the design process is smooth and progressing toward a well-developed end product for the owner.
The next phase in an energy–efficient lighting system is the development of a lighting control scheme that both meets the codes established earlier in design and incorporates the owner’s requirements. The designer should review the approved lighting fixture layout for each space and compare it to the available control methods established in the energy code for the corresponding space type. The minimum control methods identified in the selected energy code compliance path must be adapted to the program specifics.
For instance, a version of the IECC relevant to a K-12 school project may permit classrooms to be controlled by occupancy sensors, vacancy sensors and/or a time clock feature. Alternately, a university’s facility manual could only allow occupancy or vacancy sensor control of the space. If the project team is pursuing an energy incentive from the utility company, the lighting control scheme must be further evaluated to comply with the utility program requirements.
The most important aspect of the lighting control system is that designated emergency lighting fixtures in each space function during life safety events. If the emergency lighting within the space is switched and uses an emergency lighting inverter or generator as the emergency source, the control scheme must include a UL 924 emergency bypass relay to override the local lighting controls and provide full brightness of lighting fixtures for occupants exiting the building.
Alternate emergency lighting designs require the 24/7 illumination of emergency lighting fixtures within owner selected spaces that provide a secondary night light feature in the space. Once a control scheme is implemented in each space, the designer should review the lighting control system topography and connection requirements. The topography of the lighting control system is determined by the owner’s required level of monitoring and control of the lighting fixtures. The level of monitoring and control of the lighting fixture is often determined by the intended daily maintenance of the building, LEED requirements and/or utility energy rebate program requirements. These requirements should be reviewed by the owner, design team and local utility company to provide an appropriate recommendation.
Depending on the additional building systems provided by other trades on the project, interconnections of the lighting control system might be required with the building management system, fire alarm system and audiovisual/information technology systems for life safety and occupant comfort.
The next factor in completing the development of a lighting control system is specifying the appropriate manufacturer to provide the lighting control equipment. The lighting control manufacturer is selected based on its ability to meet the project’s requirements, the quality of the equipment it provides and the level of maintenance delivered to the equipment after the project is complete.
The final factor in delivering a fully developed lighting control system for the owner is designing within the project budget. It is important to monitor the lighting control budget at project milestones, via estimates, to ensure that an affordable system is delivered to the owner.
The most essential part of producing an energy–efficient lighting system is commissioning the system by an accredited design professional or third-party commissioning professional to ensure it is operating as designed. To guide and track the progress of the lighting control system for the project, the commissioning professional must be included throughout the different phases of the project, which include pre-design, design (including schematic design, design development, construction documents and construction administration), construction and occupancy. The most beneficial contribution provided by the commissioning professional is the ability to track potential issues early in the design process.
Commissioning also benefits a project to the extent that it can significantly reduce the overall energy consumption and operating cost of the building for the owner. Commissioning will ensure that the end product is acceptable and understood by the client. Both the energy code and LEED certification require the commissioning of lighting controls to be completed at the end of each project.
The best approach in commissioning a lighting system is adopting industry standard guidelines such as, but not limited to, ASHRAE Guideline 0-2019: The Commissioning Process; ASHRAE Standard 202-2018: Commissioning Process for Buildings and Systems; IES DG-29-11: The Commissioning Process Applied to Lighting and Control Systems; and various associations’ guidelines. These guidelines stress the importance of functional testing, documentation, verification, acceptance activities, providing systems manuals on all components and training the facility personnel and end users.
Enhanced commissioning for LEED, if pursued, involves either envelope commissioning or enhanced system commissioning of the building.
Once the commissioning professional and guidelines are established, the designer must absorb the commissioning professional’s review comments and requirements for each project phase. During each phase of the project, the designer will be required to illustrate different levels of information geared toward providing a clear image of project requirements.
For example, it is beneficial to include a lighting control narrative during schematic design than elaborate with a lighting control matrix, drawings and specifications in design development and contract document phases (see Figures 2 and 3). Another beneficial contribution to the contract documents is the incorporation of commissioning requirements into the book specifications. The commissioning requirements will indicate essential information such as required lighting control system testing, individual responsibilities for all parties and appropriate scheduling procedures for all test.
The ultimate goal for commissioning review in design is to resolve all issues before the construction phase of the project begins. During the construction phase, each component of the lighting control system will be performance tested. For example, each photocell will be tested to ensure appropriate dimming is provided when adequate foot-candles are delivered from the natural sunlight within the space. If any issues should arise, the problem will be documented in a deficiency log and assigned to the appropriate party for correction. The construction phase will be completed with the turnover of operation and maintenance manuals, as-built drawings, submittals and deficiency log to the owner for each lighting control element.
The final phase of commissioning consists of confirming that all testing is complete and systems manuals are maintained. If ASHRAE 90.1 and/or LEED requirements apply, a secondary commissioning professional, not involved in the design or construction, must perform the final phase. The commissioning professional will examine if each space is being used as designed. For instance, the commissioning professional will verify that time clocks are calibrated to turn on and off at the designated times per contract documents. The project is concluded with the submission of documentation by the commissioning professional indicating that lighting systems are in compliance with or exceed the performance requirements.
Providing an energy–efficient lighting system, while navigating project requirements, is one of the key components to accomplishing a high-performance building. The designer must understand the codes, controls and commissioning requirements for each project in detail to create an effective design. A successful lighting design is realized in the energy savings for the owner and the longevity of the building.