For
Section 1.3,
it is assumed that monitor use is
reduced from 168 hours/week to 48 hours/week, average power of
65 W (no power management), a U.S. stock of 46 million monitors,
and an electricity price of 8 cents/kWh. The average monitor power
and the U.S. stock of monitors were taken from Koomey, et al,
1995.
Table E.1 shows a standard PC operating pattern,
derived from observations of PCs in actual use. This is derived
from a typical scenario with 9.5 hours of on-time per day, with
four of those hours in active use and 5.5 hours in idle mode (low-power
for power-managing PCs). Idle mode is taken as the lowest-power
mode of the system . One weekday each week is taken as an "absence"
day to account for vacations, travel, etc. Power management savings
are a function of the low-power time fraction and the difference
between the full-on power and the low-power for the particular
PC or monitor. A machine on continuously, but power-managed,
would save about three times as much as the standard scenario
shows.
Table E.1: Standard PC Operating Pattern (percent of
time by mode)
"On" is the sum of "Full-on" and "Low".
"Off" is all time that is not "On".
| Full-on | Low | On | Off | |
| Standard Operating Pattern | ||||
| Workday | 16.7% | 35.0% | 51.7% | 48.3% |
| Weekend | 20.0% | 20.0% | 80.0% | |
| Absence | 0.0% | 20.0% | 20.0% | 80.0% |
| Weekday Average | 13.3% | 32.0% | 45.3% | 54.7% |
| All Days Average | 9.5% | 28.6% | 38.1% | 61.9% |
For Section 2.2, the above time distribution is used, and the combined PC and monitor power is assumed to be 140 W in active and 30 W in suspend. Eight cents/kWh (approximately the national average electricity rate) is used to estimate the dollar savings in the example.
Continue to Appendix F:
One-page Summary.
Return to the PC User Guide table of contents and home page.
Return to Appendix D: What can I do with my existing stock of PCs?.