Turning lighting OFF when it is not being used saves energy. Automating that function is the most reliable method. As a result, most commercial building energy codes require automatic lighting shutoff. This common-sense strategy also adds value to lighting upgrades in existing buildings.
To turn the lighting OFF automatically along a branch circuit, we must add a switch. This switch features a low-voltage input to accept control signals and a line-voltage output to control the load. Switching may be local, such as a vacancy sensor turning the lights OFF in a room, or remote. Remote switching concentrates switches in a central assembly that may feature intelligence, which allows programming such as scheduled ON/OFF. This assembly resides in a metal cabinet-type enclosure called a panel.
The panel, in turn, can serve as the backbone for a complete energy code-compliant control system that responds to a wide range of control inputs for indoor and outdoor lighting control. It is typically sold as a new complete unit, though panelboard retrofit assemblies are available. This article describes common panel-based lighting control systems.
Switchgear consists of power-switching devices used for electrical protection, electrical isolation, and local and remote switching. Electrical codes require that circuit breakers feed and protect each circuit. For remote lighting control, the circuit adds a switch to change the load.
The circuit breaker may integrate this switch, resulting in a controllable circuit breaker that provides both electrical protection and remote switching. Or the system may add low-voltage relay switches (called contactors when controlling very large loads). These switches typically reside in one or more additional panels installed downstream from the electrical panel. Relay-based panels may also house dimmer modules as well as relay switches.
Controllable Circuit Breakers Versus Relays
Controllable circuit breakers present advantages in:
• new buildings; and
• existing buildings where the breaker panel is not up to code.
Controllable circuit breakers are available in single-, 2- and 3-pole versions from 15-30A and from 120-480VAC. They are robust, rated up to 200,000 switching cycles. Consolidating electrical protection with switching in the same panel can reduce material cost while saving wall space.
Low-voltage relay-based systems can be advantageous when:
• the building has a code-compliant electrical panel already installed;
• a relatively small number of loads needs adding;
• single- and 2-pole relays will do the job; and/or
• the switching cycle is lower.
Relays are typically used to control single-pole 120/277VAC and 2-pole 208/240VAC circuits. Three-pole relays are available but relatively costly compared to 3-pole controllable breakers. Typical relays are rated from 20,000 to 50,000 switching cycles, though relays are available offering up to 250,000 cycles. Mechanical latching operation ensures the relay will remain in the last switched state if a power loss occurs.
Whether controllable circuit breakers or relays are used, the switch accepts input from control devices such as a timeclock, local switches, occupancy/vacancy sensors and light sensors. Low-voltage wiring connects these devices to the panel. The devices tell the switch to open or close the circuit. As such, the panel can serve as the platform for a complete energy code-compliant lighting control system:
Scheduling: Panels can enact scheduling strategies to turn lights OFF in large public spaces when they are predictably unoccupied.
Other lighting control strategies: Panels can provide switching and dimming of branch circuits based on other control inputs such as switches and sensors.
Plug load control: Specialized switches can turn OFF 50% of receptacles based on predicted occupancy, complying with the latest energy codes.
Other load control strategies: Some panels can control other building loads such as HVAC systems and dampers.
Energy metering: Some panel-based systems meter energy consumption and upload data via Ethernet connection to a central server or the Cloud for analysis using software.
Besides achieving energy savings and energy code compliance, panel-based control systems can deliver other value and benefits:
Adding a microprocessor to the panel gives the control system intelligence, allowing programming and scheduling. With an onboard lighting controller, the system operator can:
• group circuits in control zones;
• assign schedules (without needing a physical timeclock) and custom logic (IF/THEN decision-making, called the algorithm); and
• communicate directly with other panels, computers and building automation systems (BAS).
Panels are typically programmed at the panel’s frontboard, though Ethernet-based systems allow remote programming via operating software.
Panel-based systems may be centralized or distributed. In a centralized configuration, the relays reside in a centrally installed panel. Multiple panels may install for control of single floors or campus buildings. They may operate independently or be networked, with the lighting controller residing in a “master” panel and controlling connected extension panels. This provides central scheduling for all panels in a hierarchical configuration.
In a distributed configuration, very small relay-based panels (typically controlling two to four 20A circuits, see image) install closer to their controlled loads. This approach can minimize wiring costs by reducing the length of homeruns between control devices and the panel. System intelligence may be similarly distributed, allowing autonomous room-based operation, though the system may allow networking of rooms.
Networking allows data to flow between devices in a control system. Common network options include RS-485 and Ethernet.
RS-485 is a physical layer standard governing the electrical characteristics of the sender and receiver in a network. Economical, easy to install and resilient, it is often used for control signaling between panels and input devices. However, it offers limited bandwidth unsuitable for data-intensive communication such as metering.
Ethernet (IEEE 802.3), the most broadly used network IT protocol, is both a physical layer and application layer standard, thereby able to govern communication between devices. It allows more-intensive and higher-speed data, such as energy metering. Data can feed to a central server or the Cloud for software- and optionally web browser-based control and data viewing.
Connecting the System
Input devices and panels, and master and extension relay-based panels, connect using low-voltage wiring.
Standard #20 AWG Class 2 low-voltage wiring is often used to connect panels with low-voltage input devices such as switches and sensors. Plenum-rated wire satisfies plenum and riser requirements. It provides a dedicated path for low-voltage control signals.
Panels may be connected using data communications cabling. This type of wiring also connects panels to digital input devices. It typically allows bi-way communication, which enables built-in metering. Be sure to select appropriate data communications wiring and note manufacturer limits on maximum number of connected devices and wiring length.
Web-Based Control and Metering
Panel-based systems are available that can measure energy consumption and monitor real-time voltage using metering capability built into the panel. Data feeds via Ethernet connection to a central server or the Cloud. It then views in the manufacturer’s control software or recognized third-party (e.g., BAS) software via a secure web browser interface.
Using this information, facility operators can measure and compare energy consumption for different loads across buildings, departments and processes during different times of the day, week, month, season or year. This information can provide valuable insight into optimizing energy efficiency. It can verify performance of newly installed systems. And it satisfies measurement and verification requirements in programs such as LEED.
The same software also allows the facility operator to change schedules and issue commands to the control system.
Integrating a lighting control system and BAS can provide greater flexibility, efficiency and control. In an integrated system, data from a single component, such as a lighting control device, can be used to manage the overall building systems. Conversely, a single computer dashboard can control all building systems. Achieving this capability requires these systems be able to share data.
For lighting and BAS to talk, they must be use the same protocol or employ a gateway (whether a device or built-in functionality) that enables communication. The most popular are BACnet, LonWorks and ModBus. Many lighting control and BAS systems share BACnet to enable integration based on it being an open standardized protocol, though the designer must understand BACnet has various dialects, such as BACnet/IP and BACnet MS/TP. Further, the operator must decide which system will be the foundation of the integrated system, including choices of which system’s schedules and objects to use. Some solutions partially integrate, enabling the BAS to manage occupancy-based strategies while separating other strategies such as daylight response.
Another strategy is to expand the capabilities of a lighting control system, as some systems can handle HVAC, service water heater and motor loads. This might be suitable if the building currently does not have or will not have a comprehensive BAS, and if the lighting panel will have unused inputs/outputs. In this case, the panel can extend to provide many energy code-required functions, such as automatic shutoff of HVAC systems and dampers.
Additionally, the panel can configure to accept control signals from other systems, such as security systems.
It is essential that the building’s emergency lighting will not be switched according to the implemented lighting schedules, but instead operate continuously, as in the case of exit signs, or when needed during a power failure, as in the case of emergency units.
Some panels compartmentalize emergency lighting circuits to ensure they will receive power during a power failure and will operate when needed. Relays can be specified with normally closed contacts to ensure continuation of electrical contact to supply power from a backup power source during a primary power failure. Special emergency lighting remotely operated circuit breakers are also available. To verify your requirements, refer to the Life Safety Code, NFPA 101, as well as your state and local regulations and fire codes.
Panel-based systems often implement time scheduling as a control strategy. In this case, the system turns OFF the lights based on what time it is, not whether a space is actually unoccupied.
Therefore, so occupants working afterhours do not suddenly find themselves in the dark, they should be given the capability of overriding the shutoff event and temporarily keep the lights ON in their area. Energy codes typically limit the override period to 2 or 4 hours. For space controls, energy codes typically limit the maximum override zone to between 2,500 and 10,000 sq.ft., depending on the code and size of the enclosed space.
Additionally, the facility operator may require the ability to override the schedule via remote switching. In this case, the override area may constitute multiple spaces or even entire buildings. Such overrides are important when interfacing with security and fire alarm system
A typical local-area override is a low-voltage switch. This switch produces a control signal that is transmitted to the panel, which controls the load. Digital low-voltage switches are programmable and networkable. Alternately, depending on the system and desired approach, occupants may receive the ability to override the OFF event using telephones, cell phones, tablets or a PC.
After the override, the lights will remain ON until the next OFF event. When the next OFF event occurs depends on the type of system. The majority of panel-based systems operate in one of two modes.
In a sweep-based system, the OFF event occurs at a set interview during non-occupied hours (e.g., every two hours after closing time). An occupant override simply toggles the relay or breaker to the ON state. The relay/breaker remains ON until the next programmed sweep. This type of system may inconvenience occupants if they initiate an override just before the OFF sweep.
Alternately, a logic-based system can be used. In this type of system, scheduled events are programmed, and overrides are set up with preset countdown timers. If either the schedule or override is in a True state, the lights will remain ON. It may be possible with this type of system to program custom configurations using special logic commands.
Although not required by energy codes, it is generally desirable to warn occupants that the lights are about to turn OFF. For example, as long as the controlled light source is not HID, the panel can “blink” the lights OFF and ON to warn occupants. Depending on the manufacturer, the number of blinks and the time before shutoff may be specifiable.
Frequent switching poses a negligible effect on LED product life but may reduce fluorescent lamp life. If fluorescent lamps are used and lamp life is a concern, alternating lamps (if bilevel switching is employed) or some percentage of luminaires can be set to blink. If HID lamps are used, there may be task lights or other lighting in the space that can be set to blink. Alternately, an audible signal can warn occupants.