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									                              Sheffield ICT Footprint Commentary

Annual use of electricity by ICT equipment at the University of Sheffield is nearly 9,000 MWh/y,
corresponding to a carbon dioxide emission of 3,800 tonnes. It is about 18% of non-residential
electricity consumption. Electricity use can be broken down into categories as in the following table.
Note that the percentages do not sum to 100 due to rounding.
                                   MWh/y            %tage
PCs                                         4,160           48
Servers                                     1,520           18
High performance computing                  1,210           14
Imaging                                       840           10
Networks                                      690            8
Telephony                                     200            2
AV                                             60            1
Total                                       8,680

An attempt has been made to estimate the electricity used by ICT at the University of Sheffield for
HEEPI (See: http://www.heepi.org.uk/). This document sets out what is included, what is not included
and the assumptions made.
I am very grateful for guidance from HEEPI staff and for the generous help of all the staff at the
University of Sheffield who provided data for this report.

Much of the survey was based on results from equipment connected to the University local area
network which covers all the University main buildings and almost all University staff and just about
the area for which the University centrally pays the electricity bill. However there are potential gaps
(or overlaps) at the edges particularly for staff in some research groups, commercial units and health
service trusts.
Only the electricity used in powering equipment on campus has been estimated. Electricity use is
estimated at the wall socket, so no allowance is made for distribution across the campus. No allowance
has been made for the energy cost of equipment manufacture, disposal and use of consumables. No
allowance has been made for the electricity used by:
         office equipment such as franking machines, money counters, laminating machines, etc;
         by the Print Unit nor commercial suppliers for outsourced printing work;
         PCs which are often incorporated into laboratory equipment;
         PCs and printers in student bedrooms;
       portable PCs which are brought on to the campus.
The full impact of ICT equipment on space cooling and heating has not been taken into account.
Where equipment is in a dedicated cooled space such as a server room, then an overhead (40% extra)
for cooling has been added. However where equipment is in a general space which may be heated in
winter or cooled in summer, the impact of equipment heat output on space heating and cooling costs
has not been assessed.
Estimates of electricity use are derived from a number of sources, including measurement of sample
equipment, suppliers specifications or measured electrical and air-conditioning load. While these
should be broadly in line with one another, there is room for some bias in the results (for example
manufacturers figures are perhaps 20% higher than that measured for an individual sample).
In many cases crude estimates had to be made, for example over the number of locally connected
printers and how much they are used. While all reasonable efforts have been made to ensure these
estimates are sound, for example by consulting support staff in a number of departments, local practice
varies. In the end such estimates are little more than educated guesses, so not too much reliance should
be put on the detail of the results. It is however hoped that the overall magnitude of electricity used is
reasonable and robust.
Measurements were made with a Maplin power meter.1, These units are simple to use and give
repeatable results, except where the measured value is very low or changing significantly.

These are in server rooms and are run 24*7. High performance and grid computers have been
separated out, because they will feature only in universities with significant science or engineering
The University has two central server rooms which are covered by uninterruptible power supplies
(UPS) that are network connected and which will report instantaneous power (or current) figures via
simple network management protocol (SNMP). Some of the figures from the UPS are VA
measurements, so higher than Watts (W), but measurements in the past indicate that this discrepancy
should be modest, where equipment is active. The measurements were done during the day in April
2008, when weather was normal for the time of year and equipment was under a normal load.
Electricity use varies with the load on the servers. Electricity use for cooling also varies, with
The UPS covers both the air conditioning and active equipment (including servers, storage, central
phone and network equipment). These are “line-interactive” UPS units, which are understood to be
very efficient. It was not possible to separately measure the air-conditioning, but these two are
assessed together as an overhead of 40%.
A number of departments have servers offering services such as mail, web, Windows name serving.
Discussions were held with support staff from six departments, three of the larger installations were
visited and the Sun equipment maintenance contracts (though much will now be based on PC servers)
were examined to assess the extent of facilities. However there are probably twice as many centres as
this, so an estimate was made. Note further that these servers each have an IP address so an appropriate

        Maplin Plug-in Mains Power and Energy Monitor, Reference L61AQ, about £28 at the time of
writing. http://www.maplin.co.uk/Module.aspx?ModuleNo=38343&&source=14&doy=21m5
compensation has been made on the number of PCs.
Server spaces are air-conditioned and often the simplest estimate comes from this. For example, in the
case of one department they have three units rated at 10kW, 10kW and 4.5kW and can run on two out
of three so are using about 14kW. An overhead for powering the air-conditioning of 40% has been

Much of the University's central data storage is held on a Netapp storage area network split across two
machine rooms. The total storage available is nearly 50TB, of which 32TB is in use. The data is held
on 154 SATA 3.5” disks (each about 10W) and 56 FCAL 3.5” disks (about 15W) so in total, perhaps
3kW (assuming an 80% efficient power supply). With four controllers, the total load would be around
5kW. Back up is LTO3 autochange tape decks. With associated servers, it is likely that the electricity
used by storage is of the order of 10% of the 85kW total for central servers.

High Performance Computers
High performance computation is a separate requirement from general purpose server provision and
has been split out. All the high performance equipment is in air conditioned area so a 40% allowance
has been made. The central computation equipment was running at about 60% of load when tested.
Typically, only the head node of a cluster will have a visible IP network address so worker nodes would
not show up on a count of network addresses.
It has been possible to estimate the electricity used per worker node from the total load. There are
centrally, the equivalent of 220 (1u, dual socket, AMD-based) servers at Sheffield, so each is using
around 270W on average, with no allowance for air-conditioning. This roughly corresponds to
measurements made on individual servers and to the Sun calculator (dependent on memory
configuration) for their X2200 AMD based servers.2
A number of departments have local clusters. Estimates were made from the number of 1u boxes, 2-
socket boxes (nodes). Note that there are a small number of 4-socket boxes and each of these was
counted as two 2-socket boxes. The most recent HPC servers at Sheffield have used high efficiency
(HE) processors which saves about 7% of electricity when running flat out.
High performance computing provision continues to grow at a significant rates in contrast to general
purpose server provision, with additional equipment being on order at the time of the measurement.

Sheffield University has an Avaya Definity voice network with a mix of digital and analogue phones
which are generally powered from equipment in cabinets distributed over the campus, which are
protected by UPS. Around 12,000 phones are in use. The electricity used was estimated by adding the
figures from UPS reports. An allowance of 10% has been made for the extra electricity used by the
UPS units. There is a small amount of central phone equipment which is included under servers. Even
taking the latter into account, it is estimated that less than 2W of electricity is used per phone, which is
very modest.
No allowance was made for locally powered phones, answering machines and faxes. The University
        Sun Fire X2200 Server Power Calculator. http://www.sun.com/servers/x64/x2200/calc/index.jsp
has a central voice mail system and the number of fax machines is believed to be modest (fewer than
the number of photocopiers for example).

Network equipment
Hubs, switches, routers and wireless access points are run 24*7. There are good records of installed
equipment, which is highly standardised. Samples of the most commonly used equipment were
measured and it was discovered that the figure for fully connected, but idle equipment was about 20%
less that the manufacturer's published figure. The latter was used except in one case where the
published figure was three times the 4 watts measured. Five of the core switches are not in a main
machine room, but are covered by a UPS and the figure from this, 600 watts each, was used. There is a
small amount of central equipment (including a pair of central routers, YHMAN and CCTV equipment)
which is not included here, but is instead included in the servers estimate.

PCs certainly use the most electricity of any ICT equipment on campus but trying to estimate it with
any degree of accuracy is difficult. The number of PCs was estimated on the number of IP addresses
allocated to devices that were not network devices nor printers. An allowance was made for server
equipment and also for the one department that allocates its own IP addresses. About 13,000 PCs are in
PC purchase records were examined over a period of 5 years from the three main suppliers of desktop
machines to the University, which showed over 10,000 purchases. The suppliers report that most
departments follow the central recommendations which are for modest configurations. Even though
the recommendations are generally followed, there is a huge range of equipment in use, due to the rate
of change of specifications. The purchase records include some portable PCs, but many more of these
will have been purchased outside the central agreement. The figures suggest that PCs are used on
average for about 6 years at Sheffield. PC makers do not generally give specifications for power use
because of the many varied configurations. Instead estimates have been made by measuring typical
In recent months, Sheffield has specified energy efficient PCs alongside more conventional models.
These have been bought for student areas, but they cost more than other models for the same
performance and it is not yet known what the take-up from departments will be. PCs can exist in a
number of states, each of which uses a different amount of electricity as illustrated by the following
                                Off           Idle        Intense
Dell Optiplex SX280                    1             58             100
HP dx5150S                             2             43             87
Macintosh Mini                         2             22             37
Viglen VM4 Cube                        3             61             108
Viglen Genie                           1             92             149
Viglen EQ100                           3             46             59
Dell Optiplex 210L                     2             70             135
Viglen Genie Core Duo                  2             65             86
IBM X40 Portable                       2             27             37
Off is when the mains to the machine is powered up (and any power supply switch is on) but the
machine has not been powered on at the front panel. Idle is after the PC has been booted up and is
waiting for keyboard input. Intense is when the machine is actively doing arithmetic on a large dataset
and writing results back to disk. Machines can also be in Standby (for wake-on-LAN) and Hibernate
states, but the electricity used is generally similar to that in the Off state. In practice PCs are rarely
intensely used (for example when starting up, calculating a very large spreadsheet, searching a huge
file or rendering a 3-dimensional model), so the Idle figure is used for active power consumption. A
figure of 2W has been used for all PCs when Off.
On the 3000 or so managed PCs (including all central student provision), Sheffield has installed
software to switch PCs off after they have been logged out for 20 minutes. In this case it is estimated
that average use will be for 40 hours per week which allows for both office use (though office users
may not log out) and that although most student areas are in use for more than 40 hours per week,
utilisation is lower out of term time.
For other PCs, it is expected that many users do not switch the machine off overnight or even at the
weeekend. Recently 162 unmanaged PCs (in Estates, Library, Materials, MBB) were monitored using
Verdiem Surveyor.3 The report says the annual electricity use per PC is 224.5kWh (at an approximate
cost of £15). They claim that their software could reduce these costs by 26% if it was run actively to
power down PCs instead of monitoring activity. The electricity use figure was used indirectly to
estimate the average number of hours that a PC is left switched on, about 70 hours per week averaged
over a year of 52 weeks. A lot of users must be switching their PC off at night.
No estimate of the number of portable machines or high powered machines was made, instead it was
assumed that all machines were modest office ones (as most PCs bought at Sheffield are). However
some allowance on the number of PC devices was made on the assumption that they are servers run
24*7. These appear under servers. Inevitably there will be PCs of much higher specification than
recommended. However also included are low power devices such as print release stations.
For monitors, the default on modern operating systems is that they will power down to standby after 20
minutes, so the typical number of hours of active use will be about 40 hours. PCs bought in the last
four years, so about two thirds, will have flat screens which use about half the electricity of cathode ray
tubes, perhaps 30W to 40W rather than 60W to 80W. Again standby electricity use of modern flat
screen monitors is much better than CRTs, at 2W rather than about 5W. Monitors are a significant
item, contributing over one third of the power used by PCs at Sheffield.
There are 70 thin client machines in one student study space (Information Commons). These are
SunRay 270 units which have an integrated monitor and a published specification of 40W typical with
keyboard and mouse attached. We actually measured 36W with the unit powering down to 9W when
idle. When SunRay units without a monitor have been tested in the past, it was found that they did not
power down at all, and used around 7W on a 24*7 basis, which is consistent with the unit with a built
in monitor. This is much less than an idle PC but more than one which is off and there is a modest
overhead for additional server capacity.

Network connected laser printers were analysed with HP's Jetadmin software.4 This software can scan

        HP Web Jetadmin software. http://h20338.www2.hp.com/hpsub/cache/332262-0-0-225-
both HP and non-HP devices, though the devices at Sheffield are almost wholly (over 90%) HP laser
printers. The report used gives the device type and, for modern HP devices (about a quarter of the
total), the total of pages printed. By running the program twice with an interval in between, it is
possible to estimate the pages printed, which was 450,000 pages in a week. However it was not really
possible to derive too much from pages printed, because it included all the central student printers at a
busy time of year. It is also possible from the program to get the number of colour devices, which was
over 20%.
Tests of a small sample of HP units showed that the measured electricity use was close to (but about
20% lower than) the figure given by HP. HP sometimes give two or three figures for standby,
powersave and off. On some printers it is stated that the printer goes from standby to powersave after
30 minutes so the latter figure was used. The “off” figure was ignored, but it was zero or less than one
Watt.. The supplier's figure for the most common devices was used to calculate the approximate
average for Sheffield as below:
                               Standby/                         Pages per
                               Powersave           Active       minute
Monochrome                                    14            440         26
Colour                                        30            512         21

It was assumed that these devices would be printing for two hours a day, 5 days a week, so 520 hours
per year. no allowance was made for the 14 days or so in the year when the University is closed. A lot
of equipment is not switched off over this period, though use will be negligible.
Support staff in departments were contacted to estimate the number of locally attached printers. Local
practice in departments varies considerably. For example some departments have a policy of one small
laser printer per member of academic staff while another had only 10 local printers for a total of 75
staff, where there are 19 academics. Students and other staff share network printers. Monochrome
personal laser printers were much more common that inkjet printers in academic departments. Locally
connected printers are not common in service departments. An estimate, which is little more than a
guess, is that about 20% of staff have their own local printer and that the bulk of these are small
monochrome laser printers. It is thought that these will have low usage of perhaps 20 minutes per
working day.
Support staff in four departments were used to assess the number of photocopiers. It would seem that
there is a photocopier for about every 20 to 25 staff. Most of these are relatively small and often do not
support double sided copies. About a third are large devices which are often multi-function devices
devices supporting scanning, colour printing, double sided copying and binding. The bulk of devices at
Sheffield are manufactured by Sharp, who only publishes a maximum power draw figure and not a
typical operating power nor standby figure.
Measuring the power of these devices when operating is difficult and to get any accuracy would have
to be done over a period because the power use fluctuates greatly when the device is operating. The
measured value for standby has been taken, which devices return to after about 30 seconds or in some
cases as much as 20 minutes after last use. For operating power, the measured value has been
estimated from the fluctuating measured value as each sheet of paper is printed.
The library provides the student photocopying service at Sheffield. There are 34 copiers of which over
half are fast, large A3/A4 copiers. The remainder are split between slower copiers and colour copiers.
They are all Sharp models for which no meaningful power figures are published. In libraries,

photocopiers are switched off when the library is closed. Library opening times vary considerably (and
include some 24 hour facilities but on average these copiers are switched on for about 4000 hours a
year. Again use varies considerably, but is generally high and it is estimated that they spend 25% of
their time in operation.
A 52 week year was assumed for all imaging equipment usage figures.

AV Equipment
Most of the teaching space (about two thirds) of teaching space at the University is centrally managed.
In this space equipment is centrally purchased and managed. There are 144 computer projectors
installed and from the most common models installed (over 80%) of the total, the average power
consumption as stated by the manufacturer (mainly Hitachi) was 290W. The projectors generally
power themselves down to standby when there is no picture being shown. Hitachi do not publish a
figure for standby power use so this was assessed by measuring sample units. An allowance was made
for equipment in departmental space.
The Space Management Group’s figures were taken as the norm for use of central teaching space
across the sector:
“Out of the total available time, rooms were reported as being used for just over half the time”.5
Most teaching at Sheffield is between the 9 hours, 9am to 6pm, so a figure of 5 hours was taken per
day, for 5 days per week but not the whole the year to give a use of up to about 1000 hours per year of
which perhaps half, 500 hours might be used for data projection.
There are now somewhat fewer overhead projectors. Again a sample was measure to estimate power
use. No separate assessment of the PCs used by lecturers in teaching in teaching space. Instead these
are included with other PCs.
Personal Conclusions
A buying policy which focused on the full cost of ownership, including electricity, could over time
make a big change in the electricity footprint. In particular, PCs contribute most to the consumption
and a buying policy for lower power, “green” PCs, which for example meet the US Energy Star 4
standard, would make a significant difference over time. Ensuring PCs are switched off when not in
use would make an immediate difference. CRT monitors should be phased out.
There are gains to be made by consolidating services and buying all equipment so that it is most
electricity efficient in its class.

Chris Cartledge
8 July 2008

        Space Management Group, 2006. Space utilisation: practice, performance and guidelines. September 2006.

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