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Electrical Equipment News, March, p. 15, 1993-03
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Power management for desktop computers
Newsham, G. R.; Tiller, D. K.
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Power Management for
Desktop Computers
by Guy R. Newsham, Ph.D., and Dale K. Tiller, D.Phil.
Appeared in
Electrical Equipment News
March 1993
page 15
(IRC Paper No. 3024)
Reprinted with permission from
Southam Business Communications Inc.
NRCC 351 56
Power management
-
+.-
I---./
for desktop computers
As
reported in the June
1992
issue of Electrical Equipment News, electronic off ice
f
equipment is expected to have the highest growth rate of all the end-uses of energy in the
-Mmcomputer
North American commercial sector. Researchers have now studied two methods of more
on-time for a sample of 33 corn-
puters over an eight week
closely tailoring energy consumption to use, and saving energy
period, before and after stickem
reminding users to switch com-
B Y G U Y R . N E W S H A M , P H . D . , A N Dputers off were applied
D A L E K . T I L L E R , D - P H I L .
I
n a previous article ('Reducing energywastage from desktop computers" in the June 1992 issue of Electrical Equipment News), we noted that desktop computers and associated peripherals often remain switched on when they are not in use. Electrical energy is therefore wasted in two ways: directly by unnecessarily powering computers and peripherals; and indirectly through the increased load on the building cooling system. The June article described the first part of a study to define the magnitude of this waste, and to identify cost effective ways to ensure that equipment is switched off when not in use.
This article describes the second part of the project, during which we measured real computer use profiles, and examined the impact of two methods of more closely tailor- ing energy consumption to use. If successful, such methods would reduce energy con- sumption without inconveniencing the user.
Real
use profilesWe developed software, installed on a com- puter's hard disk, to record the date and time at which acomputer was switched on, and s u b sequent keyboard activity. Thus, we were able to identify periods when the computer was switched on but there was no keyboard activ- ity. For most users, this implies that the com-
puter was not being used, and so, if the com-
puter and peripherals were switched off, energy savings would accrue.
In addition, we correlated computer use to time of day, and analyzed the effects of com- puter use on peak demand.
We measured use profiles at two sites. At the first site, mean computer on-time for 33 computers over an eight week period was 42.5 hourslweek. The corresponding keyboard activity was only 4.9 hourslweek. At the sec- ond site, mean computer on-time for 16 com- puters over an eight week period was 79.8 hourslweek; the corresponding keyboard activity was again only 4.9 hours/week.
Clearly, there were many periods when the computers were on and not used, and the potential for power management was consid- erable.
Taihning power consumption to ochral use
We considered two methods of ensuring equipment was switched off more frequently when not in use. First, we designed stickers which we placed near workstations reminding users to switch equipment off. Secondly, we developed a device called Smartbar that pow- ered down equipment after a designated period of keyboard inactivity.
Smartbar resembled a regular power bar into which the computer and peripherals were plugged; however, the power supply to each of the bar's sockets was controlled by software on the host computer. The software allowed the user to select an appropriate powerdown schedule for each socket, and ensured that the computer was not switched off when an appli- cation was open. We tried both power man- agement methods, stickers and Smartbars, on different user samples and assessed their effectiveness using the monitoring software described above.
Ekiivemss
of
stickersThe upper curve of Figure 1 shows the mean on-time, in hourslweek, of 33 computers at the first monitoring site over an eight week period. The lower curve shows the mean on-time for the same sample of computers over the first eight weeks following the application of stick-
ers
.
Mean computer on-time over the eight week period dropped from 42.5 hourslweek to
36.7 hourslweek, a reduction of 14 per cent. However, the effect of thestickers appeared to wear off with time. Statistical analysis showed no significant change in keyboard activity after stickers were applied.
Ehdveness of Smartbar
The upper curve of Figure 2 shows the mean
Figure
2
-
Mean
computer on-time for a sample
of 16 computers over an eight
week period, before and after
the Smartbar power manage-
ment device was installed
on-time, in hourslweek, of 16 computers at the second monitoring site over an eight week period. The lower curve shows mean on-time for the sample of 16 computers over the first eight weeks following the installation of Smart- bars. Mean computer on-time over the eight week period dropped from 79.8 hourslweek to
29.6 hourslweek, a reduction of 63 per cent.
The reduction in mean
VDU
(visual displayunit) on-time was even greater at 82 per cent. Moreover, the effect of the Smartbars was maintained with time. Mean peak power demand was also reduced significantly. Statis- tical analysis showed no significant change in keyboard activity after Smartbars were applied.
Cost ektiveness
of
power managementThe cost effectiveness of power management is very site specific, depending on prevailing computer use and local electricity rate struc- tures. In addition, savings in cooling costs are building and climate specific.
Although stickers reduced energy con- sumption by only 14 per cent over an eight week period, stickers are inexpensive. How-
,
ever, they are unlikely to result in long term savings, as their effect appeared to wear off with time. Smartbar produced much bigger savings that were maintained with time. The device has been licensed to a Canadian manu- facturer, and is now commercially available. The manufacturer offers free audits of com- puter energy consumption to potential cus- tomers wishing to explore the cost effective ness of Smartbar at their site.Since statistical analysis showed that nei- ther of the power management methods described above sig nificantly affected user keyboard activity, we believe power manage ment of computers and their peripherals to be an effective method of reducing energy con- sumption in the office.
We wish to acknowledge the funding p r e vided for this project by the Canadian Electrical Association under project 9101 U 829, and
Energy, Mines and Resources Canada. Adetailed report on thestudy is published by CEac 1 West- mount Sq., Montreal, Que. H3Z 2W.
Smartbar purchasing information is avail-
able from Sequence Electronics, 150 Rosamund St., Carleton PI., Ont. K7C 1V2.
Guy Newsham and Dale Tiller are with the Insti- tute for Research in Construction of the National Research Council of Canada in Ottawa.
