Measured Energy Savings and Performance of Power-Managed Personal Computers and Monitors

Abstract

Personal computers and monitors are estimated to use 14 billion kWh/year of electricity, with power management potentially saving $600 million/year by the year 2000.The effort to capture these savings is lea by the U.S. Environmental Protection Agency's Energy Star program, which specifies a 30Wmaximum demand for the computer and for the monitor when in a 'sleep' or idle mode.In this paper we discuss measured energy use and estimated savings for power-managed (Energy Star compliant) PCs and monitors.We collected electricity use measurements of six power-managed Pes and monitors in our office and five from two other research projects.The devices are diverse in machine type, use patterns, and context.The analysis method estimates the time spent in each system operating mode (off, low-, and full-power) and combines these with real power measurements to derive hours of use per mode, energy use, and energy savings.Three schedules are explored in the "As-operated," "Standardized," and "Maximum" savings estimates.Energy savings are established by comparing the measurements to a baseline with power management disabled.As-operated energy savings for the eleven PCs and monitors ranged from zero to 75 kWh/ year.Under the standard operating schedule (on 20% of nights and weekends), the savings are about 200 kWh/year.An audit of power management features and configuration for several dozen Energy Star machines found only 11% of CPUs fully enabled and about two thirds of monitors were successfully power managed.The highest priority for greater power management savings is to enable monitors, as opposed to CPUs, since they are generally easier to configure, less likely to interfere with system operation, and have greater savings.The difficulties in properly configuring Pes and monitors is the largest current barrier to achieving the savings potential from power management.