Release the untapped potential of plug load control

Understanding how plug load control options and ASHRAE 90.1 enhance building performance.

10/02/2017


Learning Objectives

  • How plug load contributes to a building’s overall performance.
  • Understand ASHRAE Standard 90.1 energy mandates and building applications.
  • Explore the plug load options that are available to help specifying engineers comply with ASHRAE 90.1.

Figure 1: Installing plug load-controllable devices can lead to energy reductions of more than 21%. Courtesy: LegrandThe benefits of plug load control have been extensively proven in real-world applications. Limiting energy consumption at an electrical outlet can reduce energy waste, support an organization’s sustainability efforts, and save money on utility bills. Plug load control is also required by code in a growing number of states.

In practice, energy efficiency is one of the biggest challenges facing specifying engineers, building owners, and facility managers today. Plug load control is one of the final frontiers to conquer in terms of energy efficiency, but it can also prove the most challenging. With plug load control, one of the issues engineers face is figuring out which control method is best for their application.

Additionally, codes vary by state and even from city to city. For example, some jurisdictions have adopted ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings standards that include plug load control, some have their own codes that are similar to ASHRAE 90.1, some have codes that exceed ASHRAE 90.1, and some do not have plug load control requirements.

This can leave engineers scratching their heads, wondering what are the code requirements and what plug load control solution is right for them. But it does not have to be overly complicated.

Plug load by the numbers

A plug load is defined as the energy source used to power a device or equipment that is plugged into an ordinary ac receptacle. Data found in a U.S. Department of Energy (DOE) study shows plug load consumption is a significant issue:

  • Plug and process loads (PPLs) account for 30% of the electricity consumption in office buildings. This includes computers, printers, networking equipment, task lighting, kitchen appliances, and more.
  • Performing a plug load inventory and implementing a load-reduction strategy can reduce plug loads by 20% to 50%.

Yet, controlling plug loads does not always get the attention it should. In a National Renewable Energy Laboratory (NREL) paper presented at the 2014 ASHRAE conference, the authors wrote that “In an ultra-efficient office building, plug loads are typically one of the last end uses to be considered for energy conservation and, as a result, can account for more than 50% of the total electrical load.”

That same paper reported that occupancy-based plug load controls at a workstation reduced energy use by 21% relative to the baseline. Timer-based methods brought decreases of 26%, 46%, and 50% for workstations, break rooms, and print rooms, respectively.

Technology use is increasing, and employees in commercial settings are plugging in their personal devices in addition to office equipment. The DOE projects that by 2030 commercial energy consumption will increase by 24% and PPL energy consumption will increase by 49%. These numbers indicate controlling plug loads will be an important strategy to reduce energy consumption and costs, regardless of code requirements.

ASHRAE 90.1 and plug load control

Building and energy codes are a critical piece of the equation. That’s why it’s important for specifying engineers to understand ASHRAE 90.1 and codes like it that establish standards for plug load control.

Plug load control was added to ASHRAE 90.1 in 2010, and its requirements further expanded in the 2013 edition. Section 8.4.2 mandates that at least 50% of all 125 V, 15- and 20-amp receptacles run on an automatic control device that turns power on and off based on a schedule, occupancy sensor, or signal from another control system. It applies to private offices, conference rooms, rooms used primarily for printing and/or copying functions, break rooms, classrooms, and individual workstations. It also stipulates that at least 25% of branch-circuit feeders installed for modular furniture must be controlled.

ASHRAE 90.1, Section 8.4.2, considers three types of automatic receptacle controls:

  • Schedule-based—Also called timer-based, this type of control turns off receptacles at specific times. The code requires that an independent program schedule be provided for controlled areas of no more than 5,000 sq ft and not more than one floor, and the occupant must be able to manually override the device for up to 2 hours.
  • Occupancy-based—A sensor must turn off receptacles within 20 minutes of all occupants leaving a space. 
  • System-based—Another control or alarm system sends an automated signal that shall turn off receptacles within 20 minutes after determining all occupants have left the space.

There are three other things that are important to know about ASHRAE 90.1. First, plug-in devices cannot be used in place of hardwired controls, as they could be easily defeated by end users.

Second, all controlled receptacles must have a permanent marking to differentiate them from uncontrolled receptacles. In fact, Article 406.3 of the 2017 edition of NFPA 70: National Electrical Code goes so far as to say that the universally recognized power symbol and the word “controlled” must be permanently marked on the face of a controlled receptacle.

Third, exempt from the code are receptacles designed for equipment requiring continuous operation and spaces where automatic control would risk the safety or security of the room or building occupants.

While the focus of this article is on ASHRAE 90.1, codes vary by state and municipality. You can find local building codes at energycodes.gov.

The California Energy Code, Title 24, is considered the most stringent energy code in the U.S. Section 130.5 of Title 24 mandates that at least one controlled receptacle must be within 6 ft of an uncontrolled receptacle in private offices, open offices, kitchenette areas, reception lobbies, conference rooms, copy rooms, and hotel/motel guest rooms. The requirement can be achieved using split-wired receptacles.


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