ASHRAE Journal - September 2013 - 84

Column emerging technologies

IT and Building Loads
By mildred hastBacka; michael rutBerg; antonio Bouza, associate memBer ashrae

The total electricity consumption of information technology (IT) equipment in the U.S.
has been estimated to be roughly 100 billion kWh annually (1 quad of primary energy).1
In commercial buildings, computers alone are estimated to account for more than 0.6
quads of primary energy consumption.2 As devices related to IT operations continue to
proliferate, they are projected to continue accounting for a large share of direct energy
consumption in commercial buildings, as well as contributing strongly to commercial
building cooling load.

84

ASHRAE JouRnAl

ashrae.org

Septem ber 2013

Figure 1 Sample office building, electronic devices.3

70

1,400

1,000

other

800
600
400
200
0

networking
lighting
imaging
displays

60

networking
lighting
imaging

50

displays

computers

30
20
10

computers

Device Count

40

Annual Energy Use (MWh)

other

1,200
Number of Devices in Use

Technical approaches to reducing IT energy consumption (and commensurate cooling load) include power
shut-off devices, equipment upgrades, power management software, virtualization of desktop and server
infrastructure, and local area communications based on
passive fiber optic networks.
Among commercial IT devices are desktop computers
and monitors; laptop computers; projectors and other
displays; imaging equipment including copiers, scanners
and printers; servers; small networking equipment; and
uninterruptible power supplies (UPS). The number of
these devices and the total energy consumed varies widely
across commercial sectors; for example, banks and financial services facilities are relatively IT-intensive compared
to, say, industrial wholesale operations.
Figure 1 shows results from an analysis of energy and
power data, collected at the device level, in a sample
office building.3 Computers represent about 15% of the
number of devices in use but account for about 45% of
the annual energy use. Networking devices account for
about 5% of devices in use but more than 10% of annual
energy use. Imaging equipment also accounts for more
than 10% of annual energy use, although this category
represents less than 5% of devices in use.
The average operational plug load of IT equipment is
typically about 5 W/unit for small devices such as chargers and network components, 20 W/unit for laptops,
35 W/unit for LCD desktop monitors, 65 W/unit for
desktop computers and computer servers, 215 W/unit
for network laser printers, and 1100 W/unit for a copy
machine.4 For a prototypical small office, the aggregate
of this IT equipment can account for 65% to 70% of the
total peak plug load density, or 0.4 to 0.6 W/ft2. A total

Annual Energy Use (MWh)

0

reduction of about 20% to 25% in plug load power (about
0.1 W/ft2) could be achieved by using ENERGY STAR®
rated equipment for all IT equipment, by increasing
the proportion of laptop computers relative to desktop computers, by using power management software
(whether implemented on a per-machine basis or centrally managed over the network) for all computers, and
by deploying outlet occupancy sensor controlled outlets
for non-critical devices such as monitors.5 2013 ASHRAE
Handbook—Fundamentals, chapter 18, includes data and
methods for calculating the impact of IT equipment on
cooling load for non-residential buildings.
A relatively new and fast-growing option for managing
computer-related building loads is virtualized desktop
infrastructure (VDI). VDI is a system of software managed
Mildred Hastbacka is a director and emerging technologies scout and Michael Rutberg is
a senior technologist in the Mechanical Systems Group for TIAX LLC, Lexington, Mass.;
Antonio Bouza is a technical manager with the U.S. Department of Energy, Washington, D.C.
ASHRAE Journal - September 2013

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