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Did you know that next to lighting, plug load equipment is the highest consumer of electrical power in a building? And plug load consumption continues to grow as more electronic devices are added every year. This increase in consumption runs contrary to energy saving goals. While the efficiency of electronic devices continues to improve, efficiency alone can’t stop the trend. That’s why energy codes, including the California Energy Commission’s Title 24, Section 130.5 (d), includes a requirement for receptacle control.
But how does receptacle control help save energy? The highest efficiency electronic equipment still consumes power, even when “hibernating”. By disconnecting the power at the receptacle, the consumption goes to zero. Devices like computer monitors, desk lamps, printers, microwave ovens and chilled drinking fountains can all be turned off when the building is unoccupied to save a significant amount of energy without any disruption to the occupants.
What does the code say?
Many academic and government studies prove receptacle control saves energy with a positive ROI. That’s why the 2013 edition of Title 24 requires controlled receptacles in private offices, open office areas, reception lobbies, conference rooms, kitchenettes, and copy rooms. For each uncontrolled receptacle, a controlled receptacle must be provided within 6 feet. This convenient mix of controlled and uncontrolled receptacles allows an intelligent choice of which equipment to control.
Many buildings are built with flexible open space. The code is written to ensure that receptacle control is in place for these areas. One way to comply is to have workstations with built-in receptacle controls installed and operating at the time of final permit. But if compliant workstations are not installed, built-in, hardwired power controls must be provided in the building infrastructure. Controllable, plug-in power strips are not allowed in any location since they can be easily removed.
What determines when it’s time to turn off receptacles?
Receptacle control requires a control signal. The control signal can be from an occupancy sensor, a time clock or a signal from another system, such as a building management or security system. The signal indicates when an area is typically or actually unoccupied.
An occupancy sensor makes sense for small areas, such as private offices. A single occupancy sensor can provide sufficient coverage and control a small number of receptacles.
Time control is a more reliable choice for larger areas, because occupancy sensors requiring line-of-sight view are affected by unknown variables such as the placement of partitions, file cabinets or other objects. Some devices, such as drinking fountains and network printers, are not practical to control with an occupancy sensor. For this reason, time control is the more universal control method.
Which control method makes the most sense for my project?
A time schedule defines non-business hours when receptacles may be shut off. But an occupancy sensor can further determine when it may be appropriate to shut off receptacles during business hours, like when people are away from their desks. Occupancy sensors save additional energy by turning off receptacles during these unpredictable intervals.
There are many different design approaches using time control, occupancy sensor control, or a combination of both. All have different costs and provide different levels of energy savings. The 2012 Summer Study on Energy Efficiency in Buildings, by the American Council for an Energy-Efficient Economy evaluated scenarios ranging from 100% time control to 100% occupancy sensor control (You can find the report, “Integrated Lighting and Plug Load Controls,” in Section Three of the proceeding’s table of contents. Although occupancy-sensor control captures additional energy savings, the study found that the cost per square foot could be double the cost of implementing a time control solution. Unfortunately, the incremental energy savings from using an occupancy sensor are not enough to offset the additional expense, resulting in longer payback times. While occupancy sensors control a single area, time controls have multiple channels to leverage the cost over many areas. All considered, it turns out that the most practical and cost effective approach is to employ a mix of control methods, with occupancy sensors deployed in small areas and time control in large areas.
What power switching solution makes the most sense?
Occupancy sensors typically use an auxiliary relay pack installed in the ceiling near the sensor. A switch leg from the receptacle circuit is routed up to the relay pack. Although simple, this solution requires additional conduit, a junction box, more wiring, and labor standing on a ladder.
A more convenient option is a relay panel installed in the electrical closet. Circuits originating in the breaker panel route through the relay panel on their way to the receptacles. Although installing this option has a cost, it is typically lower than the installed cost of many individual, distributed relay packs. A built-in, multi-channel time controller can be less expensive than the installed cost of many sensors.
A third option eliminates the relay panel by providing switching in the form of a controllable circuit breaker. This option allows the electrical contractor to route wires directly from the distribution panel to the controlled receptacles, same as the uncontrolled receptacles. This option has the lowest cost of installation since a circuit breaker panel is required anyway. And, best of all, controllable breaker panels don’t require extra space in cramped electrical closets.
Among the options available to specifiers is Square D’s Powerlink G3 controllable breaker panel. Our brochure on Powerlink Lighting Control Solutions outlines the system’s range of control and monitoring capabilities.
