Tremendous advances have been made in reducing energy use in commercial buildings over the last decade. The introduction of LED luminaires and lamps has made lighting a much smaller contributor to overall building electricity use. With energy consumption from building systems falling, efficiency advocates are looking closer at how the devices and equipment we use in those buildings add to total demand.
On the surface, this might seem like overreach. Really, just how much effect could the desk fan and table light in an office cubicle have on a building’s annual electricity bill? A decade ago, this would have been a reasonable question. But today—with a growing emphasis on neutralizing our buildings’ environmental impact—every kilowatt of demand can matter. This is why plug loads, including everything from office workers’ computer monitors to break-room refrigerators, are being eyed for more efficient operation by the latest versions of energy standards and codes.
A bigger piece of the pie
Plug loads have become important precisely because of the progress that has been made in reducing demand from systems that once were energy hogs in commercial and institutional buildings, such as office buildings, stores and schools. Lighting accounted for roughly 40 percent of all electricity use in buildings in 2003, according to the U.S. Energy Information Administration. By 2012 (the most recent year with available data), that figure dropped to 17 percent, and that was before the LED transformation had begun in earnest. Plug loads accounted for 14 percent in 2012, or almost even with lighting.
“Forty years ago, lighting loads were about 6 watts per square foot—now they’re half a watt, so basically, we’re probably using 2.5 percent of what it took to light a building 40 years ago,” said Charles Knuffke, systems vice president with Legrand’s Wattstopper division. “Now the microscope is falling on the plug load. It just stands out.”
The full impact of a building’s worth of connected coffee pots and photocopiers has recently been felt in the growing number of projects aiming for zero-net-energy performance. These buildings are being designed to use no more energy than they produce on-site, through roof- and ground-mounted solar panels and other approaches.
The new environmental education center on the campus of Williams College, in Williamstown, Mass., is one such example. There, energy engineers modeled the structure’s anticipated energy use down to the last kilowatt in their efforts to meet the standards of the Living Building Challenge, an ambitious, performance-based environmental-certification program. After one year of operation, the building had met six of the program’s seven performance criteria. Energy use was the sole outlier. Plug loads, including unmonitored kitchen appliances, were seen as a major hindrance in meeting this goal.
This is why developers of energy standards and building codes have become much more interested in providing options for turning power off in vacant spaces, in standards such as the American Society of Heating, Refrigerating and Air-Conditioning
Engineers (ASHRAE) Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings. ASHRAE 90.1 is referenced by many state and municipal building codes.
On the state level, there are codes such as the California Energy Commission’s Title 24 energy code. Though Title 24 is only enforced in California, it often influences both outside codes and manufacturer’s product designs. The most recent editions of both documents require at least half of all electrical receptacles to be controlled by the same kinds of occupancy sensors mandated for commercial lighting systems, so connected equipment is turned off when monitored spaces are vacant.
"Monitors, table lamps, space heaters, fans and printers are excellent candidates for use with a controlled receptacle to avoid using energy when there is no one in the space using the devices." —Michael Jouaneh, Lutron Electronics
Plugging into new options
While occupancy-sensor installation for lighting control is becoming common knowledge for electrical contractors across the United States, knowing how to use similar approaches to control electrical receptacles appears to be a bit spottier. Because each state, and some individual municipalities, might reference different editions of standards such as ASHRAE 90.1, awareness of the approaches for addressing what standards call automatic receptacle control (ARC) varies widely.
“It seems contractors are generally aware of these requirements in the states that use ASHRAE 90.1 2010 or newer for their energy code, but not so much in the other states,” said Michael Jouaneh, manager of sustainability and energy standards at Lutron Electronics.
Alabama, Delaware, Mississippi, New Jersey and Oregon are referencing more recent ASHRAE 90.1 editions, and California’s Title 24 has similar ARC requirements.
“But, even when contractors are familiar with the code requirements, they are less familiar with the solutions,” Jouaneh said.
Felix Omar Perez, a product manager for Hubbell Wiring, added Florida and Washington to the list of states requiring ARC, and agreed that knowledge outside those areas is lacking.
As with occupancy-based lighting controls, ECs have a choice of wired and wireless options for establishing a connection between a wall- or ceiling-based sensor and the receptacles being controlled. Alternatively, controlled receptacles can be connected to a new or existing sensor-based building management system. The decision to go with wired or wireless products is largely one of preference.
“A good wireless system requires very few additional components for retrofit applications, especially if you have an existing lighting control system,” Perez said.
However, he knows not all electrical professionals have come on board with this approach.
“Wired, though, is still preferred by the traditional electrical contractor, especially in new construction,” Perez said.
Depending on the standard being referenced, ECs also might have the choice in how they meet the requirement that half of all receptacles in a space be controlled—either using an equal number of evenly distributed controlled and uncontrolled dual-outlet receptacles, or by using split-wired products featuring a combination of controlled and uncontrolled receptacles.
“Split-wired duplex receptacles provide the most flexibility for the end-user, because furniture layouts change with time,” Perez said. This could leave future occupants without easy access to the type of receptacle they need.
With either option, building occupants will need to recognize that receptacles marked with the slotted-circle symbol that commonly indicates a power switch on electronic devices will be turned off if the space is left vacant for more than 30 minutes.
For Knuffke, this marking, recommended by the National Electrical Manufacturers Association, might be too subtle. Something more visibly recognizable could help both the less technically savvy and those scrambling under a desk to find a nearly out-of-sight socket.
“My personal recommendation to designers is to not only have that symbol, but if possible, do some kind of colored differentiation,” Knuffke said. “Most people aren’t going to know what that symbol means.”
Legrand employees have personal experience with what becoming familiar with these new devices can entail. When the company moved into new offices fitted with controlled receptacles, many were stumped by the devices.
“It was a nice, new office that met the new energy codes, and even our own people didn’t really understand the marked receptacles,” Knuffke said. “You can’t assume that everybody in an organization understands what’s going on.”
This education process also might include helping customers work through exactly what devices and appliances should not be connected to a controlled receptacle. Some examples, such as clocks and refrigerators, are easy to understand, while others might not come so quickly to mind.
“You should avoid plugging computers into a controlled receptacle,” Jouaneh said, referring to desktop and tower computers that could be damaged by frequent power cycling. “But monitors, table lamps, space heaters, fans and printers are excellent candidates for use with a controlled receptacle to avoid using energy when there is no one in the space using the devices.”
Knuffke has a tip to consider in this decision-making process.
“If you’ve got something on a UPS strip, that’s a pretty good indicator you don’t want that equipment connected to a controlled receptacle,” he said.
As ECs know well, standards and codes are continually evolving documents, generally revised on three-year schedules. So, as ECs and their customers get used to controlled electrical receptacles, what can they expect in future efficiency standards? Knuffke said he is seeing power measurement show up in some jurisdictions’ “reach” codes to get buildings beyond current levels of performance.
“So, what I’d anticipate seeing is, not only is the control going to be mandated, but at some point, they’re going to want to see how power is being used,” he said. “It’s really hard to control what you don’t measure.”
Jennifer Amann, director of the buildings program with the American Council for an Energy-Efficient Economy and a long-time observer of standards development, expects plug loads to remain a topic of developers’ attention over the coming decade. But, like Knuffke, she sees growing interest in putting actual-use data to work, to understand how to improve equipment and systems across a broader range of load conditions.
“We’re going to see an increased interest in plug load and process load, and I think we’ll also see a big role in refining the standards we already have,” she said. “As technology continues to advance, I think we’ll continue to see opportunities.”
Among such opportunities is the possibility of shifting focus from specific equipment mandates toward more performance-based targets.
“It’s a shift to a new way of defining compliance,” Amann said. “I think we’re going to find opportunities to engage on energy efficiency and better understand the savings that come from things like much more integrated design, which are such an important part of getting into super-efficient buildings.”