- THE MAGAZINE
Plug loads — devices that plug into wall outlets — represent a growing, but hard to quantify, portion of commercial building utility bills. A new study revealsdetailsabout the actual energy consumption of a wide range of common plug loads for two commercial buildings in California. The project report alsodetails measured savings of 40 percent or more resulting from the implementation of a variety of low-cost efficiency measures, and it identifies areas for future research that may prove invaluable to energy managers and utility program managers alike. The energy-saving measures identified in this study can be used to reduce plug load use in any commercial building.
Plug loads account for an estimated 20 percent of the electricity consumed in U.S. commercial office buildings. Although voluntary programs and mandatory regulations have played an important role in improving the energy efficiency of plug load devices, the growing numbers of office electronics products in service, coupled with the use of faster, more powerful equipment, have resulted in an overall increase in plug load energy consumption. Reversing this growth trend will require a more precise knowledge of where energy is being used and the identification of strategies for cutting that use. To address this need, the California Energy Commission’s PIER program funded researchers from Ecova (formerly Ecos Consulting), supported by PECI, and the New Buildings Institute to survey plug load energy use and assess opportunities to reduce that use through relatively simple measures in two highly efficient buildings: a 95,000-square-foot public library and a 14,000-square-foot office in California (both recently LEED certified).
Researchers began by inventorying the equipment in use in the two buildings and recording power draw data at one-minute intervals for one month on 100 energy-intensive devices such as computers, computer monitors and peripherals, and imaging equipment (printers, copiers and multifunction devices) to establish an energy-use baseline.
The data shows that desktop computers were by far the largest source of electricity consumption at both sites — representing an estimated 68 percent of measured plug load energy use at the library (Figure 1) and 69 percent at the small office (Figure 2). Computer monitors were the second largest plug load energy users at the library and the third largest at the small office, accounting for 20 percent and 9 percent of total studied plug load energy use, respectively. Collectively, researchers found that computers and monitors accounted for 90 percent of plug load energy use.
This data also revealed several sources of excessive energy use that could be reduced without any negative effects. Researchers found that the desktop computers, LCD monitors and imaging equipment that were in place typically drew more active power than the most efficient models available today. Compounding this problem, 62 percent of desktop computers at the small office and 40 percent of staff (nonpublic) computers at the library were often left operating in active or idle mode overnight and on weekends, needlessly using energy during these times. Similarly, most imaging equipment and computer peripherals (such as computer speakers) were found to be rarely used but to draw power continuously in idle mode when not in use. Finally, researchers found that some individual pieces of equipment, such as imaging equipment and projectors, consumed enough energy to make them worthy targets for savings measures.
Cutting Energy Use
To address these problems, researchers identified three different approaches involving software, hardware and occupant behavior. They then deployed these low- and no-cost energy-reduction measures on 39 of the metered devices, and monitored energy consumption on all 100 devices for an additional month to measure the savings. The savings measures included:
- Software Power Management Settings. Enabling and properly programming existing power management settings of computers and imaging equipment provided the largest energy savings opportunity, with a reduction of 13 percent achieved at the library. However, this figure is lower than predicted by other studies because the group policy at the city level overrode the changes made by the researchers at the library. If adequate software is already installed on the system — which it often is, especially on newer equipment — this solution can be implemented at no cost.
- Hardware Control Strategies. Several cost-effective control devices can be employed to turn off equipment when it is not in use. Timers and timer plug strips, which turn off devices at set times, were found to reduce electricity use significantly (as much as 43 percent on a workstation comprised of LCD monitor, laser printer, computer speakers and calculator), making them good options to control devices with regular operating schedules. Load-sensing power strips, which automatically shut off the peripheral devices on the plug strip when the main device (typically a computer) enters a low-power mode, can also be highly effective. Annual energy savings of 46 percent were measured on a load-sensor plug strip controlling a computer monitor, laser printer and computer speakers. These so-called “smart” strips are easy, low-cost ways to eliminate the energy used by often-forgotten computer peripherals.
- Occupant Behavior Measures. Researchers found that even simple, inexpensive behavioral measures, such as calendar reminders that encourage employees to turn off equipment at night and on weekends, reduced desktop computer electricity use by an average of 6 percent.
Researchers noted that although purchasing new hardware can reduce energy use, the absolute cost of new equipment is often large relative to the dollar value of the annual energy savings. Therefore, they recommend buying higher efficiency equipment at the time of replacement rather than discarding functioning equipment to buy something new. When buying new equipment, they recommend a procurement policy use the TopTen USA lists for computers and monitors. TopTen is a nonprofit organization that works to identify and publicize the most energy-efficient products currently on the market in a wide range of different categories with the goal of helping users save as much energy as possible when making a new purchase.
More Research Needed
In addition to providing valuable information regarding real-world energy consumption and savings opportunities from plug loads, the study highlights the following research needs:
- Servers and Server Closets. While not a focus of this study, researchers observed that the energy use of server closets is growing, but little documentation of server closet energy use is available.
- Standardized Definitions. A universal plug load taxonomy that can be expanded to include new devices and technologies as they come to market would help researchers keep track of the energy use of these devices.
- Demand Impact. Variations in power draw over time under a variety of conditions for most plug load devices are still poorly understood. Thus, there is a need to explore load duration curves of key plug load devices in different geographic regions and building types.
- Incremental Cost Data. Researchers found that little incremental cost data was available for efficient models of office equipment. That data is needed to help managers develop the business case for more efficient equipment.
- Behavior Savings Potential. Noting that building users play a critical, but poorly understood (and often overlooked), role in building energy consumption, researchers suggest undertaking additional research to identify and quantify the savings potential of various behavioral measures such as energy-use readouts.
Overall, the data collected leads researchers to suggest that California’s energy efficiency standard for buildings, Title 24, should consider a requirement for plug load peak power density. Limitations on allowable plug load density would, in turn, allow building engineers to reduce air conditioning capacity, saving on the capital cost of HVAC equipment and its subsequent operating cost. In addition, given the large amount of energy used by imaging equipment, the researchers indicate that California could benefit from the inclusion of efficiency requirements for that category in the state’s energy efficiency regulations for equipment (Title 20). Other devices that were found to be larger energy users, such as mounted projectors and mailing machines, could also be covered by efficiency requirements in Title 20. On a national level, the results of this study suggest that the U.S. Department of Energy might benefit from developing federal energy-efficiency standards focused on imaging equipment and desktop computers to go alongside the standards already in development for devices like television sets and set-top boxes.
For more information, see the full report: Commercial Office Plug Load Savings assessment at http://bit.ly/LsnCn8.
What is PIER?
The Public Interest Energy Research (PIER) program funds research and development in the fields of energy efficiency, renewable energy, advanced electricity technologies, energy-related environmental protection, transmission and distribution, and transportation technologies. To accomplish this, PIER enlists businesses, utilities, energy companies, public advocacy groups and world-class scientists at California’s universities and national laboratories. In the last decade, PIER has invested more than $700 million to bring market energy technologies that provide environmental and economic benefits to California’s ratepayers.