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Saving Energy Through Improved User Interfaces

Electricity saved through power management of office equipment has been one of the premier success stories for the energy-efficiency community. The U.S. Environmental Protection Agency and Department of Energy's Energy Star program was largely responsible for creating aggressive lowpower—or "sleep"—modes in nearly all forms of office equipment. The devices can automatically shift into a sleep mode after a user-determined length of inactivity and then quickly recover for use when needed.

Power Control User Interface logo

Despite this success, many devices that have power management features are not saving energy because the power management features are disabled, incorrectly configured, or thwarted by hardware or software conflicts. The number of products in use that have power management turned on vary widely with the kind of equipment and situation. Surveys have found that the great majority of PCs do not have power management turned on. For monitors, printers, and copiers, the enabled rates are above 50%, but significant improvement is still possible.

A comprehensive study of office equipment energy use conducted at EETD presents a snapshot as of 2000. This study found that the "power management gap" for office equipment in the U.S. was about $1.3 billion per year—energy that could be saved if power management was enabled on all devices that have this feature. Although it is difficult to predict what the actual savings from improved interfaces will be, we estimate that 35% of the potential savings could plausibly be realized, resulting in a savings of $470 million annually (Table 1).

Table 1. Office Equipment Energy Consumption and Savings from Power Management
United States
Total Office Equipment Electricity Use
(GWh/year)
71,100
Potential Savings — 100% Power Management
(GWh/year)
16,700
Likely Impact of the User Interface Standard
(GWh/year)
5,800
Savings of each 1% of Potential (GWh/year) 170
Total Office Equipment Electricity Cost
($mil/year)
5,700
Potential Savings — 100% Power Management
($mil/year)
1,300
Likely Impact of the User Interface Standard
($mil/year)
470
Savings of each 1% of Potential ($mil/year) 13

Notes: From Kawamoto, 2001. All figures annual for end of 1999. Electricity rate is 8 cents/kWh. The "likely savings" figure is based on achieving 35% of the potential energy savings from increased use of power management. The existing savings from power management are 22.8 TWh/year for the U.S., with a dollar value at the above electricity rates of $1,800 and $380 million/year. The existing savings are with respect to no use of power management, and the "potential savings" reflect 100% enabling of power management — both with no change in manual turnoff rates.

Designing the power management interface for all office equipment so that users clearly understand which symbols mean "on," "off," and "sleep" and which state is currently active, can maximize the energy savings from power management. We believe that an interface standard, tested on users and agreed to by equipment manufacturers, can realize the predicted energy savings.

The Problem and the Research Process

With funding from the California Energy Commission's Public Interest Energy Research Program, we have, in consultation with the private sector, developed and tested a new interface standard that could capture some of the savings now being lost.

Five different examples of the sleep symbol.

The Berkeley Lab study determined that, from device to device, many terms, symbols, and indicators are used differently or are not clear to begin with. On many devices, power management controls are difficult or impossible for the average user to find. Many PCs don't indicate to the user when the equipment is in a low-power mode, so many users are unaware that the PC can "sleep." Users can't always tell whether PC power management is working, and many don't realize that PC power management is distinct from the monitor power management. An important example is the "standby" problem. The term can mean anything from a "fully on" state to a lowpower mode or the amount of power used by a device when it is functionally off.

We conducted research in two phases. We first gathered a wide variety of data about products and related topics such as existing standards, cultural issues, and accessibility, and drew on the literature of user interface design. Next, we developed and tested proposed interface standards.

We worked closely with an industry advisory committee. Industry is interested in the user interface because it seeks to improve the usability and friendliness of electronic office equipment, which reduces customer service requests and may increase product sales. A Professional Advisory Committee, of equipment manufacturers helped refine the project plan for our research.

In devising a proposed standard, we developed a simple vocabulary of user interface elements that are adaptable to a wide variety of devices. What we had to work with was a large number of power-related symbols, colors for indicator lights, and device modes and states—with a bewildering variety of labels, including such words as Ready, Sleep, Active, Energy-Saver, Power-Save, Idle, Suspend, Doze, Standby, and Low-Power. Our goal was to reduce the possibilities to a single, simple set of easily understandable terms.

Results—A Recommended Standard Interface

We developed various interfaces and tested them at Berkeley Lab, UC Berkeley and Cornell to determine how well users understood various types of symbols, indicators, and equipment states (e.g., "sleep" versus "off"). From this work, we wrote the draft standard summarized in Table 2.

Table 2. Key Elements of the User Interface Standard

Static Interface

  • Use only three power states when possible:On, Off, and Sleep
  • Use the word "Power" for terminology about power.
  • Refine the A circle with a short vertical line extending from its center through an opening at the top of the circle. symbol to mean "power" as for power buttons and power indicators; use the Closed circle with a single vertical line through the middle. symbol (on/off) only when necessary.
  • Use the "sleep" metaphor for entering, being in, and coming out of low-power states; use the moon symbol — Crescent moon. — for sleep.
  • Adopt "green/amber/off" color indications for power state indicators.
  • Present PC "hibernate" modes as a form of off.

The standard also covers "dynamic behavior" or how devices behave over time and in response to input or activity. For example, the standard specifies using "power up" to mean turn on or wake up, "power down" for turn off or go to sleep, with flashing green on the power indicator for powering up and flashing amber for powering down.

Next Steps

In September 2002, the Institute of Electrical and Electronic Engineers (IEEE) created a working group (#1621) for a "Standard for User Interface Elements in Power Control of Electronic Devices Employed in Office/Consumer Environments." This group is being formed now to adapt the User Interface Standard content into an IEEE standard. In the long term, we hope to work with international standards organizations. The standard is intended to be voluntary, and updated as power management technology changes.

We need to explore other areas in which user interface improvement and standardization could save energy, including lighting, space conditioning, and real-time pricing. Research has shown that thermostat controls are poorly understood by many users; making these devices easier to use will substantially increase the energy they save.

— Bruce Nordman

For more information, contact:

  • Bruce Nordman
  • (510) 486-7089

For more information, visit the Power Management Controls web site.

For the project's final report and detailed recommendations, see:IEEE 1621, the "Power Control User Interface". This work is funded by the California Energy Commission's Public Interest Energy Research Program.

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