Today code requires the use of controlled receptacles in non-residential buildings. But best practices for incorporating these now code-mandated devices are unclear, causing confusion in the field.
By requiring automatic control of the power available at the receptacle, these codes are curbing large amounts of energy historically consumed by plug loads in commercial buildings:
While these codes are explicit regarding the number of receptacles that must be controlled and the location of those devices in the building, they leave important details up to the discretion of the designer and building engineer.
For example, some of the codes require that receptacles turn off automatically but allow the design team to determine whether the receptacles respond to a time-of-day device, occupancy sensor or automated signal from another control or alarm system. Selecting the control mechanism for these controlled receptacles impacts the complexity of the circuit design and installation as well as the potential energy savings created by these devices.
The National Electrical Manufacturers Association (NEMA) published a white paper that explores good, better and best practices for incorporating controlled receptacles on a project. The paper, titled Automatic Receptacle Control to Meet ASHRAE 901-2010 and California Title 24, identifies options designers may consider and highlights some of the strengths and weaknesses of each approach.
The NEMA paper compares the technique of hardwiring receptacles to the breaker panel and controlling them on a preset schedule with various methods for incorporating controlled receptacles that respond to occupancy.
Hardwiring the receptacles to a panel and controlling them on a schedule most closely mirrors the way standard receptacles are wired for power; this approach may also require the fewest changes from a design and installation perspective. But it also may be the most limited regarding flexibility and energy savings. An occupancy sensor-based system turns off plug loads when an area is unoccupied regardless of the time of day; this creates a better fit between the energy available at the receptacle and the energy that is needed, thus increasing potential energy savings. Unfortunately, this approach may also be more intense when it comes to design and installation; it requires more circuits and more contemplation in the design of the circuits, as they must fit the building usage patterns and schedules from an occupancy-based standpoint.
Luckily, new technologies are making it easier to incorporate occupancy-based receptacle control into a space. Fixtures with integrated occupancy sensors offer a more flexible solution for coordinating plug load power with the presence of a single person. Wireless controlled receptacles, in which the receptacles are wired for power, but control signals are communicated wirelessly, reduce the necessary wiring and conduit runs by more than 50 percent when compared with the needs of traditional hardwired solutions. The eliminated control wiring makes wireless receptacles easier to design and install. In addition, these code-compliant, wireless controlled receptacles are more flexible, offering both schedule-based and occupancy-based control options.
For more information on the NEMA recommendations for incorporating controlled receptacles into a new or existing building, download the NEMA white paper. For specific project-related questions, please refer directly to the code of interest or the authority having jurisdiction.