Driven by commercial building energy codes, green building projects and owner demands for flexibility and lighting energy savings, lighting controls increasingly are being specified and specified systems are becoming increasingly sophisticated.
As complexity increases, the benefits of stronger functionality increase; however, so do risks of poor design, installation and lack of user acceptance. In a perfect world, designers provide very detailed requirements for control functionality and installation that electrical contractors and users, in turn, easily understand. In the real world, owners may not have clear expectations, design documents may fail to communicate intent, installers may commit errors, and end-users may complain.
An effective lighting design includes a valid controls design that, in turn, requires clearly expressed design intent.
A number of best-practice tools describe lighting and control functionality, including the written control narrative, control zoning, one-line wiring schematics, equipment specifications and cut sheets, panel schedules and device settings, and performance-testing criteria.
• The written lighting control narrative describes the system and includes a sequence of operations or a description of what the system does in response to specific inputs (sensors, schedules, etc.). This is sometimes called the basis of design or the design intent.
• Control zoning visually describes which control devices control which loads.
• One-line wiring diagrams provide a topology for the control system, showing how the devices connect and relate to each other.
• Equipment specifications and cut sheets describe all of the products used on the project and their desired minimum performance.
• Lighting and electrical panel schedules assign loads to specific power switching and/or dimming devices residing at the panel.
• Device settings include light level setpoints, time delay and sensitivity adjustments for occupancy sensors, integrated dimmer presets, time schedules for relays, and more.
• Performance-testing criteria informs the commissioning authority and electrical contractor how and what to test the system for after it is installed.
The written control narrative is a critical component because it informs almost everything else, yet it is often missing in project documentation. It is important primarily because it provides a simple roadmap for all project participants regarding the functionality of the lighting control system. It goes beyond what drawings can communicate.
To be more specific, the control narrative guides the preparation of contract documentation and specifications, provides clear direction to contractors and manufacturers during bidding, ensures that the commissioning authority has clear performance-testing criteria, and explains to the owner how the control system operates.
For designers, it can increase the likelihood of delivering a quality lighting system and intended solution and reduce risk across the construction process to ultimately satisfy the owner’s project requirements. Different participants—lighting designers, architects, electrical engineers and, in some cases, electrical contractors—may be involved in designing and specifying the control system, and the entire team should have access to the same clear guidance on its functionality. For installers, it can reduce the possibility of error and dissatisfaction and associated callbacks. For the commissioning authority, it provides a clear reference about expectations and how to test to ensure what is delivered satisfies the owner’s requirements. And, the owner, operations and maintenance personnel and users will receive a quality product and know what to expect from their control system, increasing the likelihood of acceptance.
In the future, more precise documentation may become the norm for two reasons. First, the green building market continues to grow. Part of this growth is adoption of requirements by various jurisdictions that certain buildings either meet a green building code (based on ASHRAE 189.1) or achieve green building rating (e.g., LEED).
Second, commercial building energy codes may require it. The ASHRAE/IES 90.1 2010 energy standard, for example, requires the following documentation to be turned over to the building owner within 90 days after control system acceptance: record drawings of the actual installation, submittal data for all lighting controls, recommended schedule for inspecting and recalibrating controls, and a complete control narrative showing “how each lighting control system is intended to operate, including recommended settings.”
The control narrative should be considered an evolving document that may change or become a little more complete as the project moves from predesign (programming) to design (schematic design, design development, construction documentation) to construction, and occupancy and operations. At each step, changes are reviewed and approved.
As there is no literary standard for how a control narrative should read, designers should use whatever tools work best for them. That being said, the basic document may be considered to have at least two primary components:
1. A general description of project goals and delivered control strategies deployed to satisfy these goals
2. A description of the control system and sequence of operations for each space or space type
Here is an example of very general project goals, including relevant codes, for a new office building: “The lighting controls must meet the mandatory control requirements as defined in the ASHRAE/IES 90.1-2007 energy standard. Select control strategies implemented by the lighting systems go beyond these requirements to support LEED certification.”
So we know lighting will be turned off when not in use, and strategies not required, such as daylight harvesting and personal dimming control, may be considered to reduce energy consumption and potentially generate LEED points. Obviously, the more direction the owner provides about the project requirements, the more responsive the design can be to owner needs.
Next follows a general description of the control strategies used in the project: “The interior lighting controls will enact two primary strategies intended to minimize energy consumption: 1) automatic shutoff via occupancy sensors in small, enclosed spaces and via a timeclock-based low-voltage control system in larger, open spaces, and 2) daylight harvesting in all spaces receiving high, consistent levels of daylight contribution, notably the main lobby and private and open office spaces. In certain spaces lacking daylight and where personal safety is an issue, such as corridors illuminated by electric lighting, select lights will remain on at all times during normal hours of occupancy. In presentation spaces, notably the meeting and training rooms, flexibility will be provided to enable users to select preset light levels. Lighting controls will also turn exterior lighting on/off using a photocell/timeclock based on curfew (grounds lighting) or dusk-to-dawn operation (security lighting).”
Then comes a description of the lighting controls to be installed in each space, including a sequence of operations—that is, a description of what the controls in the space do and in what response to various inputs such as occupancy, time event or daylight levels.
This part could be done several ways. One way is a straight written narrative for each room type. For example, for each type of room (e.g., private offices), there could be a description of the load, what controls are installed and how they work in the space. Another approach is a matrix, as shown in Figure 2. The example office building is broken down into space types, and the control strategies are identified for each. In the far right columns are two codes. The first connects the control system to wiring diagrams in the construction documents. The second describes the control system used in each space type and how it works within that space type. This approach works particularly well for complex projects where there are a lot of individual space types. Instead of space types, we might use room numbers pulled from the drawings.
Let’s return to the example office building. In the open offices, we will use a combination of control strategies including manual-on, timeclock-off and daylight-harvesting dimming in perimeter zones receiving sufficient daylight levels. The control narrative for the manual-on and timeclock-off switching controls (code 2 under the “sequence of operations” column on the matrix) might read, in language adapted from the Department of Energy’s Commercial Lighting Solutions webtool: “On/off control of the general lighting in each open office area will be controlled by a combination of manual wall switches and timeclock schedule functionality residing in a low-voltage relay panel-based control system.
“Users entering the space at the start of business hours will turn the general lighting on by control zone, with each zone being within 2,500 square feet in area or per the local energy codes.
“At 6 p.m., the control system will blink several times, warning users that the lights will turn off in five minutes. At 6:05 p.m., the control system will turn the general lighting off. Users working after-hours may keep the lights on, or turn the lights back on, by toggling the manual wall switches, which function as a 120-minute override for the timeclock automatic shutoff system.
“After 120 minutes, the system will blink the lights again, and sweep them off five minutes later unless the override is again activated.”
From there, we can add even more features about the control system itself; the more detailed the narrative, the more likely users will benefit from intended performance. Here are additional requirements: “The control system shall be programmable at a microprocessor-based central processing unit (CPU). The system shall provide weekly routine and annual holiday scheduling and automatically adjust for leap year and daylight savings time. Each program shall not exceed 25,000 square feet or one floor, whichever is smaller. The control system shall have 10-year nonvolatile memory that stores all schedules. The system shall be able to reboot the program and reset the time schedule and current time, without errors, following power outages up to 14 days in duration. The system shall export lighting energy-consumption reports by space and zone. The control system shall operate independently of but be capable of communicating with the building automation system, if present.”
Additionally, we might add performance-testing criteria as a basis of commissioning of the control system, required in many larger building projects, LEED projects and projects complying with codes based on the ASHRAE/IES 90.1 2010 energy standard. For our low-voltage relay control system, this might include ensuring that the general lighting in each zone turns off at the scheduled time, that the sweep is properly preceded by a blink (or other) warning, that the overrides are properly zoned and working, etc.
Finally, we might add references to other pertinent documents, such as control zoning and equipment specifications.
Obviously, all of this takes time and effort at the front end of the project, but it can be well worth it. In the end, the rationale for a written control narrative is simple: By providing clear, detailed and current communication about the design intent, designers of lighting control systems can reduce design and installation risks while increasing the likelihood of an energy-saving, quality control system that satisfies its owner.
Thanks to Gary Meshberg, LC, LEED-AP, Encelium Technologies.
DILOUIE, L.C., a lighting industry journalist, analyst and marketing consultant, is principal of ZING Communications. He can be reached at www.zinginc.com.