Economics of lighting systems
Codes and standards, energy efficiency, lighting controls, and plug loads all play into specifying lighting and lighting controls in nonresidential buildings.
- Assess the various codes, standards, and guidelines that guide lighting design.
- Outline the various lighting control systems.
- Make use of cost analyses to determine the correct lighting and lighting controls.
Designing lighting systems has become progressively more complex. New energy codes require designers to deliver appropriate illumination with less energy; this also increases the sophistication of lighting control systems. In response to these changes, a variety of strategies and technologies have given the industry different methods of tackling these energy codes.
While many building clients are interested in seeing these systems integrated into their projects, they all have the same question: How much is it going to cost? Understanding the strengths of different approaches can help lighting designers specify a lighting system design that meets owner requirements while still meeting the necessary codes.
Codes and standards
A key driver to the increasing complexity of lighting systems are changes in energy codes. These codes have become stricter by lowering the amount of energy allowed for most building types and spaces (see Table 1). The predominant energy code impacting lighting energy allowances in the United States is ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings, of which different versions are adopted throughout the country (including the 2007, 2010, and 2013 versions). The U.S. Dept. of Energy’s State Energy Code Adoption Map provides details on the specific codes used in each state. Depending on the part of the country, the energy code in affect could vary by as much as 0.65 W/sq ft (family dining) to as little as 0.08 W/sq ft (museum). ASHRAE Standard 189.1: Standard for the Design of High-Performance Green Buildings also should be considered.
Optional energy initiatives also are playing a role in lighting system design. Programs such as U.S. Green Building Council’s LEED, Living Building Challenge, GreenGlobes, and International Living Future Institute’s Net Zero Energy Building Certification are putting tighter restrictions on designers to use even less energy than required by state-mandated codes. Government or municipality work often requires compliance with some of these (or other) optional standards. As such, it is important to research what optional standards may be applicable prior to performing any design. Knowing the impact of these standards early on is critical to designing a lighting system that meets or exceeds code requirements.
While the energy allowed for lighting has decreased, the amount of recommended lux or footcandles for a task or space has hardly changed (see the Illuminating Engineering Society Handbook for recommendations). This leaves designers with two fundamental approaches for reducing energy while maintaining lighting levels:
1. Task-oriented lighting: Task surfaces are illuminated to the recommended lighting level for the task and function, and the surrounding spaces are illuminated at a lower level. This can be accomplished by having a general level of lighting and supplementing with task lights (desk lights, under-cabinet, wall-washing, etc.) or by having the overhead ambient source strategically located over the task areas. This approach can be cost-effective, as it can result in fewer ambient luminaires and targets the lighting where it is needed.
2. Efficient luminaires: Select luminaires that optimize the amount of lumens delivered to the work surface while minimizing the Watts used. Following this approach effectively means using LED or T5 fluorescent sources. While LED luminaires are often still more expensive than non-dimmable fluorescent luminaires, they become more economically viable when compared to dimmable fluorescent luminaires.
As energy requirements become more restrictive, designers are forced to use a combination of these two strategies to meet code.
Energy-efficient lighting systems
Two predominant technologies have been employed over the past decade to provide energy-efficient lighting solutions. The first is the use of T5 or T5HO linear fluorescent lamps. The smaller size of the T5 and T5HO lamps, as compared with older T8 or T12 lamps, allows the lamp to block less reflected light in the luminaire and allows for higher efficiencies by delivering more lumens from the lamp to the space. The second technology that has been used to achieve greater energy-efficient lighting is the use of LED luminaires. LED technology continually strives to improve the luminous efficacy (i.e., delivered lumens/Watt) of LED luminaires, and they have now reached the point where LED luminaires have a higher luminous efficacy than fluorescent luminaires in many cases. The luminous efficacy of an LED product has become a critical metric in understanding the energy efficiency of LED luminaires.
One point where LED luminaires start to “shine” from an economic perspective is that most LED luminaires include some level of dimming (typically down to 10%) as standard without an upcharge by the manufacturer. A higher-caliber dimmer for LED luminaires (down to 1%) is still typically an extra cost. When comparing similar LED and fluorescent luminaires with basic dimming (down to 10%), the cost difference between the two often shows dimmable LED luminaires to be equivalent to or less expensive than fluorescent luminaires.
As more projects implement LED luminaires, they subsequently open the door to increasing the level of control adjustability. When LED luminaires include the ability for dimming without an increase to luminaire cost, users and designers can take advantage of the technology and begin adding dimming controls. However, adding dimming-control devices increases the cost of the lighting control system. Use of LED luminaires is ideal for projects where daylight harvesting is desired, as the inherent dimming capability of LEDs reduces the overall cost of the daylight-harvesting system in comparison to a similar system using fluorescent luminaires. The ability to dim the LED luminaires also lends itself to load shedding (i.e., demand-response), in which the client or the utility can automatically dim the luminaires throughout the facility (≤ 10% reduction) to save energy.
Additionally, some codes (California Title 24-2013) and standards (LEED IEQ Credit 6.1—Controllability of Systems: Lighting) require luminaires in spaces to be adjustable to multiple levels of lighting. This can be achieved by having multiple zones of lighting, by using step-dimming ballasts or multiple ballasts in fluorescent luminaires, or by using fully dimmable luminaires. The specifics regarding these requirements need to be evaluated based on the standards in question.
Lighting controls are easily becoming the most complicated concern for understanding the economics of a lighting system. The increase in code requirements has mandated minimum functionality for controls, increasing the complexity of the lighting control system. However, there are several different methods to meet these code minimums. Still, lighting control systems can range from the relatively simple to the complex.
At a fundamental level, there are three different approaches to the technology of lighting control systems:
1. Standalone control: Each switched leg and/or space operates independently.
2. Centralized control: A lighting control panel acts as the brains of the system and regulates the automatic control of the luminaires.
3. Distributed control: A networked lighting control system allows the control of the switched leg or space to be local to the luminaires while interconnecting separate zones so that they can be controlled on a master level.
These three approaches can be used either exclusively or in various combinations at the same facility. For example, a private office with a few luminaires and a wall switch motion sensor may be all that is required to meet code. Tying this room back to a central control panel or distributed system may be more costly and unnecessary. Similarly, an electrical room that is not required to have any automatic controls due to safety concerns would not need to be tied into any control system and would only have a standard light switch (i.e., standalone control). At the same time, open office spaces at the same facility could use either a centralized control system to control the lights via a time-of-day schedule or distributed control system to control the lights via motion sensors. In my experience, using a combination of the three approaches provides a cost-effective approach by allowing the designer to select control methods in line with the code requirements and the client’s budget.
When selecting the overall control strategy, it is necessary to first understand the minimum code requirements to determine where each of the three control approaches can be used. After determining the minimum code requirements, it is necessary to determine the client’s requirements. These two factors will help zero in the control strategy that’s best-suited for an individual client. Tables 3 and 4 reflect a relative order of magnitude of controls costs based on observation of lighting control costs and by consulting with lighting controls representatives. The intent is to illustrate a relative order of magnitude when selecting between standalone, centralized, or distributed control systems. In addition, these tables reflect a relative cost magnitude comparison between using time-of-day controls versus motion sensors. The order of magnitude in cost varies as you move from looking at an individual room to looking at an entire facility.
There are many different factors that influence the amount of capital that a client is willing to invest in the lighting systems. A client that is also the owner of the building has a stronger interest in investing in the infrastructure of the building and on achieving possible energy savings over the long term. A client who is a tenant of a building doesn’t have a long-term commitment to the location, and, therefore, may look for options with a shorter payback period. From experience, leasing clients tend to want “code minimum” compliance while owner clients tend to range between “code minimum” and “energy efficient” goals. Understanding if a client is interested in a short-term payback “code minimum” approach versus a long-term payback “increased energy efficiency” approach is important in selecting a lighting system to match the client’s needs and expectations.
Figure 1 illustrates a sample project, showing an estimated initial cost and the estimated present value of the annual cost (i.e., annual energy cost) over 20 yr. Each column shows the magnitude associated with using different levels of control complexity. The more complex lighting control system has a higher initial cost. As more complex automated control features are instituted (i.e., motion sensors, daylight harvesting, plug load controls), the operational costs over time begin to decrease. While this is just one example, the principles apply in many applications. Specific lifecycle cost-benefit analysis should be performed to evaluate individual project needs and requirements.
Designing lighting systems today requires the designer and the client to answer several critical questions before beginning the design:
- What are the minimum code requirements?
- How long will the client be in the space? Does the client own or lease the space?
- Is the client willing to pay a higher initial cost to potentially have lower operating costs in the future?
- What level of controls beyond the code requirements does the client want?
Having frank discussions with clients on the mandatory requirements, as well as the pros and cons of additional controls, allows designers to narrow the lighting system options to suit the client’s needs. As stricter code requirements evolve, it becomes increasingly necessary to communicate with owners, contractors, and designers of the increased cost of these control systems so that budgets can be adequately prepared and expectations aligned for projects.
Bidding lighting control systems
Functionally speaking, there should be little or no operational difference between a centralized and a distributed control system. The difference lies with the equipment, installation, and maintenance of the system. As such, it may be more cost-effective from an initial costs perspective to specify the control performance required in an individual area while allowing vendors to submit either type of control system. This method allows lighting control representatives to target the most effective technology and the most cost-effective solution for the given performance requirements. It also is important to get an estimate on the installation cost, as one system may have a lower equipment cost but a higher installation cost while another may have a higher equipment cost but a lower installation cost.
Brian Fiander is an electrical engineer at Harley Ellis Devereaux, specializing in lighting design and specification. He serves as one of the firm’s sustainable design champions, acting as a resource for other staff members regarding green design, LEED certification, lighting, and electrical systems. He has designed lighting systems for various projects across the country.