Plug Load Frequently Asked Questions (FAQ)
- Who needs to know about plug loads?
- What core concepts can I learn from this FAQ document?
- What are plug loads?
- How do plug loads use energy?
- Why do we care about plug loads
- Can’t equipment power management reduce plug loads?
- What can we do to reduce plug loads?
- What outcomes can we target?
- What are best practices for reducing plug loads?
- Research and Citations
Plug loads are “orphans.” Until recently, no one really took notice of plug loads. They were not considered important, and no one had the responsibility to track or manage them. But, that is changing. As buildings become more energy efficient, the significant impact of plug loads becomes more apparent. In high efficiency buildings, plug loads may account for more than 50% of the total energy consumption.
This FAQ document is a result of information compiled from research on plug load programs addressing energy impacts in government, private, and institutional facilities. Research citations are included in the text below and are summarized at the end of this document.This Plug Load FAQ can help identify no-cost and low-cost options to reduce plug loads and illustrates the growing need to “adopt-a-plug load.”
Research shows that the most successful approach to reducing plug loads is an integrated team approach. Plug load reduction programs need an organized team and a “champion” to lead it. The champion should be a charismatic leader who understands the dynamics of facilitating an integrated team, and is enthused with rallying people around the “cause.” Facility Managers, Facility Operators, and Energy Managers are the people who are most responsible for energy use and operations at federal facilities. They may be in the best position to support and lead an integrated team approach.
The team should include a broad range of perspectives - those who use the equipment, those who maintain the equipment, as well as those who may determine (or influence) which types of equipment are purchased/leased. Ideally, the team includes members representing Finance, Procurement, Facility Operators, Office Managers and Office Staff (equipment users). They will be valuable contributors to determining options and solutions for the plug load program. The more they know about plug loads the more the program can apply no-cost and low cost solutions.
- Plug loads are significant factors in energy budgets.
- Plug loads can be addressed for existing buildings as well as new construction.
- There are no-cost and low cost options available to reduce plug loads.
- As buildings become more energy efficient, plug load reduction becomes more relevant.
- Plug loads have not been predominant in many energy reduction programs and therefore have not had “champions.”
- An integrated team approach is essential to the long-term success of plug load management strategies.
Plug loads are energy used by equipment that is usually plugged into an outlet. “Computers and monitors accounted for 66% of all [plug load] devices; office electronics (printers, faxes, multifunction devices and computer speakers) accounted for 17% of all devices; miscellaneous devices (portable lighting, telephones, and coffee makers) accounted for the remaining 17% of all plug load devices.” (Moorefield, L., et al. 2008). Other devices included in the research include battery chargers, vending machines, and refrigerators (Roberson, J. et al. 2004).
Plug loads are not related to general building lighting, heating, ventilation, cooling, and water heating, and typically do not provide comfort to the occupants.
Modern electronic equipment usually incorporates a variety of power levels, or “modes” and is usually “on” continuously at some power level. The various modes allow for power management of the equipment – correlating the power mode to the user’s activity level. Most common modes are active, standby, and off. Active mode powers equipment as it is being operated, and is the most energy intensive. Standby mode leaves equipment on, but powered-down either automatically when the equipment has been idle for a specified time, or manually placed in standby by the user. Electronic devices will return to active mode when a user engages the equipment. Off mode either does not draw any power or draws very little power because it has been manually turned off or unplugged by the user. Many electronic devices never completely turn off in order to start quickly when the user activates the device. These are called “parasitic loads.” For example, the DVD player has been switched off using the remote, but it is still connected to the power socket and so continues to draw a small quantity of power. Parasitic loads are also known as “phantom loads” or “vampire loads.”
Plug loads can be surprisingly large. Minimizing plug loads is a primary challenge in the design and operation of an energy-efficient building. Plug loads in commercial buildings account for almost 5% of U.S. primary energy consumption (NREL 2011). On average, plug loads account for approximately 30% of electricity in offices (Moorefield, L., et al. (2008). In minimally code-compliant office buildings, plug loads may account for 25% or less of total energy consumption; in high efficiency buildings, plug loads may account for more than 50% of the total energy consumption (Poll, S. and C. Teubert 2012).
Aggregated impacts of plug loads are significant. As an example, researchers (Moorefield, L., et al. 2008) estimated that California’s office plug loads consume more than 3,000 gigawat hours annually, costing business owners more than $400 million each year. The associated carbon dioxide emissions of these plug loads is more than 700,000 metric tons annually—equivalent to the carbon dioxide emissions of 140,000 cars during one year. The equipment inventory showed that offices contained on average 7 devices per employee and 30 plug load devices per 1,000 square feet of office space.
Research reveals that power management does not operate in isolation, but rather is subject to complexities of the workplace environment. For example, a problematic aspect of devices “waking up” is the delay in activating. This delay often frustrates users. Equipment is often left in active mode when not in use - especially networked equipment. (Roberson, J. et al. 2004). Energy Star labeled products have factory installed power management settings that require the device to enter a low power mode, however users, administrators, and software updates often disable these settings. Several reports studied trends in turn-off rates and concluded that turn-offs were reduced in the more recent studies.
Power management was found to be most successful in monitors and laser printers, and least successful in desktop computers, inkjet printers, copiers, and fax machines (Roberson, J. et al 2004). This study utilized a three-year previous study and considered related trends in commercial buildings, education buildings, medical buildings, and offices. It reported that of the computers inventoried during their after hours survey, only 6% of turned-on computers had power management enabled. Turn off rates for computers (36%) and monitors (29%) were somewhat lower than the study 3 years prior. Power management rates for monitors (72%) were higher by 16%. Power management was lowest in high schools and small offices and highest in universities and large offices. This may indicate the influence of centralized IT departments and effective occupant behavior policy.
The referenced research papers provide recommendations and strategies for reducing plug and process loads. Several identify a team approach. For instance, the report on NREL’s Research Support Facility (NREL 2011) [PDF] recommends project design though an integrated team, and a strategy as follows:
- Establish a plug loads champion.
- Develop a business case for addressing plug loads.
- Benchmark your conventional equipment and operations.
- Be willing to identify occupants' true needs.
- Meet needs as efficiently as possible.
- Turning it all off.
- Institutionalize plug load measures through procurement decisions and policy programs.
- Address unique miscellaneous plug loads.
- Occupant awareness, education, and feedback.
- Encourage the design team to identify applicable plug load strategies.
See Plug Load Management Plugload Checklist [PDF - 98 KB].
The NREL facility design team was contractually required to meet a whole-building energy use goal that included plug loads. To accurately account for plug loads, the team required input from NREL on previous and proposed equipment and use. A team (owner, tenants, engineers, architect, IT, procurement staff, facility operator and NREL researchers) helped in making decisions about efficient plug loads and was assigned to be plug load champions.
Other effective strategies employ interventions such as choosing energy efficient equipment to replace legacy equipment, setting effective energy policies, promoting beneficial occupant behavior, and employing plug-load controls such as load sensing and scheduled timer controls. (Poll, S. and C. Teubert (2012).
Best practices can include no-cost and low-cost options. Variables affecting project targets may include project budget, and projected return on investment (ROI). But, plug load reductions in the 50% range are achievable. As an example of a successful plug loads reduction effort, NREL’s Research Support Facility had the goal of becoming a “net zero” office facility. In order to reach this goal, NREL would need to achieve a 50% reduction from estimated legacy plug loads energy use (NREL 2011). Their plug and process load is estimated to be 18.5 kBTU/ft2/yr – reduced from projected baseline of 35.1 kBTU/ft2/yr.
In addition to utilizing an integrated team approach, research highlights the following plug load interventions:
Enable power management features: (Kawamoto, K., Y. Shimoda, et al. 2004) (Webber, C. A., et al. 2006)
By enabling the power management in computers, the energy use in non-business hours can be decreased by 60%. Reducing time delays can reduce it even further.
For copiers, when power management is built-in and properly functioning, about 90% of the energy use in non-business hours can be saved.
For laser printers, without power management, about 50% of energy is used in non-business hours, and 45% of energy is used during idling in business hours. Power management in laser printers based upon these data could reduce energy used by up to 95%
Install schedule timer plug strips: (Moorefield, L., et al. 2008) (Acker, B., et al. 2012) (Metzger, I., et al. (2012)
Plug strips included in the research are schedule timer plug strips, occupancy and load-sensing plug strips. Timed plug strips out perform all other plug strip interventions.  The payback period for a $100 device was best for the schedule timer controls, at an average of 3.425 years for all devices combined. The average payback period for the load-sensing controls and occupancy sensing was 30.5 years and 13.9 years for all devices combined.
Before implementing smart plug strips consider the cost of energy at the site, and whether centralized solutions are in place to switch non-essential systems on and off.
Energy efficient equipment: (Roberson, J. et al 2004) (NREL 2011) (Acker, B., et al. 2012) (Moorefield, L., et al. 2008) (Nordman, B., et al. 2000) (Lobato, C., et al. 2011)
Specify energy efficient Energy Star equipment, and pay special attention to parasitic loads in order to use efficient equipment in the most efficient manner.
Replace desktops with laptops when appropriate. Laptops are 76% more energy efficient than desktop computers. Desktops are in active mode about 30% of the time whereas laptops are in active mode only 10% of the time. On average, desktop computers are in standby or sleep 50% of the time and disconnected 7% of the time. Laptops are in standby or sleep 58% of the time and disconnected 26% of the time.
Replace CRT monitors with LCD monitors. CRT monitors used 14-49% more power than LCD monitors depending on the mode, though 79% of monitors inventoried were LCD monitors.
Laser printers, multi-function devices and inkjet printers. Inkjet printers and multifunction devices are 70% more energy efficient than laser printers. For laser printers without power management about 50% of energy is used in non-business hours. For laser printers with power management, 45% of energy is used during idling in business hours. Among the sample of printers, 46% were laser and 34% were inkjet. (Roberson, J. et al 2004). The turn-off rate was twice as high (30%) for inkjet printers as for laser printers (15%); inkjet printers are more likely to be turned off than laser printers because they are much less likely to be networked.
“Nonrated equipment must be researched to find the most efficient model, which should be turned off when not in use, if possible. Parasitic loads require special attention, even if the equipment is energy efficient. There will always a more efficient way to perform operations. This is accomplished by using more efficient equipment in a more efficient manner.” (NREL 2011)
NOTE: Plug load management teams should consider that the building occupants and equipment users typically know best about a facility’s and workforce’s needs. ROI of equipment upgrades and occupant behavior modifications must consider the trade offs between environmental impacts and worker productivity. For instance, laser printers may be considered most productive because of high speed printing, double side printing, collation, etc. Inkjet and multi-function devices may be more relevant in small offices and for specific office environments.
Occupant behavior modification: (NREL. 2011) (Poll, S. and C. Teubert 2012) (Metzger, I., et al. 2012)
Provide occupant training. Lack of occupant training can lead to disabling of controls. Many users are annoyed by delays of power management, and so disable it or set a long time delay like 60 minutes. Technological innovation to shorten the inconvenience of wake-up from power management is necessary to achieve more energy savings by power management.
Work with IT to allow occupants to power down at night. Though not technically part of automatic power management, the degree to which people turn off equipment by hand can be as important to energy use and savings as power management. Research shows power management can reduce energy demand by over 60% (Nordman, B., et al. 2000). The desktop turn off rate was 36% (laptops not included), CRT monitors was 32%, and LCD monitors was 18% (Webber, C. A., et al. 2006).
Establish effective energy policies (Poll, S. and C. Teubert 2012). From the energy perspective, changing energy saver policies to transition to the lowest power mode (standby) was found to save more energy than schedule-based control where loads were completely de-energized during off-hours. This is especially effective on devices such as computers, monitors, copiers, and printers. However, from a productivity perspective, a balance must be struck between energy savings and inconvenience to users due to wake-up times delays. For monitors, the wake time is typically insignificant; but for printers and copiers, the warm-up times can range from a few seconds to minutes.
GSA has recognized the significance of energy and related environmental impacts of office equipment and engaged contractors to provide research of relevant literature on process and plug loads. Research papers cited for plug loads include the following:
- After-hours power status of office equipment and energy use of miscellaneous plug-load equipment; Judy A. Roberson, C. A. W., Marla C. McWhinney, Richard E. Brown, Margaret J. Pinckard, and John F. Busch. (2004).
- Assessing and Reducing Plug and Process Loads in Office Buildings; NREL. (2011). Golden, CO.
- Office Plug Load Field Monitoring Report; Moorefield, L., et al. (2008). Portland, OR, Ecos: 74.
- Energy saving potential of office equipment power management; Kawamoto, K., Y. Shimoda, et al. (2004). Energy and Buildings 36(9): 915-923.
- Pilot study of a plug load management system: Preparing for sustainability base; Poll, S. and C. Teubert (2012). 2012 IEEE Green Technologies Conference, April 19, 2012 - April 20, 2012, Tulsa, OK, IEEE Computer Society.
- Energy conservation potential of power management for fax machines; Newsham, G. R. and D. K. Tiller (1995)." Energy and Buildings 23(2): [d]121-130.
- Office Building Plug Load Profiles; Acker, B., et al. (2012); Boise, ID., University of Idaho: 53.
- Reducing plug and process loads for a large scale, low energy office building; Lobato, C., et al. (2011). NREL's research support facility. 2011 ASHRAE Winter Conference, January 29, 2011 - February 2, 2011, Las Vegas, NV.
- PC and monitor night status: Power management enabling and manual turn-off; Nordman, B., et al. (2000). Proceedings ACEEE Summer Study on Energy Efficiency in Buildings 7: 7.89-87.99.
- After-hours power status of office equipment in the USA; Webber, C. A., et al. (2006). " Energy 31(14): 2487-2502.
- Plug-Load Control and Behavioral Change Research in GSA Office Buildings; Metzger, I., et al. (2012). GSA Green Proving Ground Program. NREL: 47.
 (Acker, B., et al. 2012) The report also suggested a need for future work surrounding the effect of smart plug strips and occupancy sensors to control outlet power and the implementation of user education campaigns to raise awareness of the total power contribution of plug loads. Of the plug strip interventions (occupancy sensor plug strips and load-sensing plug strips), savings per device controlled was comparable. The average savings with the occupancy sensor plug strip was 16.97% during the weekday, 28.39% during the weekend, and 36.22% during the holidays, for a total average of 27.19%. For the load sensing plug strips, the average savings was 19.75% during the weekday, 25.14% during the weekend, and 38.41% during the holidays, for a total average of 27.77%.