Energy Efficient Computing

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Energy Efficient Computing

by Faulkner Staff

Docid: 00021312

Publication Date: 2205

Report Type: TUTORIAL


For all its many benefits, information technology comes with considerable
costs. While the costs associated with the acquisition of hardware and
software assets are well-known and well-documented, the costs of powering
IT systems and devices – the energy costs – are still not fully
appreciated. For example, as of the most recent study performed in 2014,
data centers in the US consumed an estimated 70 billion kWh – 1.8 percent
of total US electricity consumption. At issue for data center operators,
as well as enterprise users and regular consumers, is how to make
computing more energy efficient – not just to save money, but to lessen
the impact of computing on climate change.

Report Contents:

Executive Summary

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For all its many benefits, information technology comes with considerable
costs. While the costs associated with the acquisition of hardware and software
assets are well-known and well-documented, the costs of powering IT systems and
devices – the energy costs – are still not fully appreciated.

Energy costs are significant in two ways:

  1. Economic – To maintain their competitiveness,
    enterprises need to lower their operational expenses, including
    electricity, a major contributor.
  2. Environmental – Enterprises need “to do their part”
    to protect the planet against the ravages of climate change, which is
    due, in large measure, to the byproducts of electric generation.
    Consequently, many, if not most, enterprises are committed to realizing
    the goals of “green computing,” with the reduction of CO2
    emissions as a key objective.

Initiatives aimed at affecting energy efficient computing are primarily
targeted at two communities:

  1. Data center managers who invoke techniques like server
    virtualization to reduce their equipment "footprint", thus reducing their
    energy consumption.
  2. Enterprise managers and consumers who are encouraged,
    for example, to buy ENERGY STAR-qualified PCs and monitors.

Implementing Energy
Efficient Computing

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While there is no standard formula for achieving energy efficient
computing, the typical approach is to seek out incremental savings which,
when aggregated, will represent a substantial decline in overall energy
demand. For example:

Correctly configuring desktops can save up to 60 percent of the
power they would normally consume.
Virtually all desktop
computers are equipped with Power Management Systems (PM) which allow fine
grained control of energy use. If enabled, PM systems can exert control
over when and how deeply displays, hard drives, and processors ‘sleep”.
(Devices are said to enter sleep states when hardware throttles
back its power consumption and places itself in a very low power stand by
mode. This behavior is usually triggered after some defined period of user
inactivity.) There is typically little performance penalty for the user.
In the “lightest” sleep, any touch of the mouse or keyboard reawakens
hardware in seconds. Even configuring devices to use this lightest form of
sleeping can save on the order of 60 percent of the energy that would be
consumed by a fully powered but idle device.

Server virtualization can reduce server farm power utilization. An
energy optimized data center server farm can deliver multiple paybacks
including reduced energy consumption, better hardware utilization, and
dramatically reduced heat output. A key strategy for achieving better
server farm energy performance is concentrating virtualization. Being able
to run more processes on a single server allows some servers to be shut
down during off peak demand periods.

Application software can be engineered for lower energy use.
Personal computers are designed to be in processor idle 75 percent of the
time, but in typical use cases, this happens something closer to 90
percent of the time. An idle processor is available to sleep, and while in
a sleep state, the CPU saves most of the energy it would otherwise
consume. Well designed software promotes the ability of processors to
assume sleep states, and only interrupts sleep when there is productive
work to be done.

Exploiting parallel computing can save energy. Today’s
PC design trend is away from the use of single, fast CPUs and toward
more cores operating in parallel, but at lower speeds. (A central
reason for this is that faster processors generate more waste heat, a key
design limitation in devices like laptops and tablets.) Better use of
parallel programming technology is the key to getting more work per unit
of consumed power out of multi-cored systems.

Data Center Energy Efficiency

In addition to these individual steps, a more holistic approach to data
center energy efficiency is being pursued. As of the most recent study
done in 2014, data centers in the US consumed an estimated 70 billion kWh
– 1.8 percent of total US electricity consumption.1 Thus,
reducing data center consumption is a primary objective.

As a partial guide to implementing energy efficient data centers, the
Pacific Gas and Electric Company has articulated seven key principles:

  1. “Specify and utilize high efficiency power supplies in Information
    Technology (IT) computing equipment. High efficiency supplies are
    commercially available and will pay for themselves in very short time
    frames when the total cost of ownership is evaluated.
  2. “Inactive servers can use [a large percentage] of full computational
    power. Consolidation measures such as server virtualization increase
    server utilization factors and therefore increase server computational
  3. “For a modern, heavily loaded installation with [dozens of] racks,
    use of high efficiency power supplies alone could save [thousands of
    dollars] per year and decrease the square-footage required for the IT
    equipment by allowing more servers to be packed into a single rack
    footprint before encountering heat dissipation limits.
  4. “Cooling load and redundant power requirements related to IT
    equipment can be reduced …, allowing more computing equipment density
    without additional support equipment (UPS, cooling, generators, etc.).
  5. “In new construction, downsizing of the mechanical cooling equipment
    and/or electrical supply can significantly reduce first cost and lower
    the mechanical and electrical footprint.
  6. “When ordering servers, specify power supplies that meet at least the
    minimum efficiency recommendations by ENERGY STAR.
  7. “When appropriate, limit power supply over-sizing to ensure higher and
    more efficient load factors.”2

Individual User Energy Efficiency

To reduce individual consumption – both enterprise and consumer – the US
Department of Energy recommends the following:

ENERGY STAR-labeled office equipment is widely available. It can provide
dramatic energy savings – as much as 75 percent savings for some products.
Overall, ENERGY STAR-labeled office products use about half the
electricity of standard equipment.

To avoid “vampire” loads, unplug non-critical equipment, or better yet
connect them to a smart power strip and use the switch on the power strip
to cut all power to the appliance(s). Many appliances continue to draw a
small amount of power when they are switched off. These vampire loads
occur in most appliances that use electricity, such as DVD players, TVs,
stereos, computers, and kitchen appliances. Unplug battery chargers when
the batteries are fully charged or the chargers are not in use.

Use rechargeable batteries for products like cordless phones and digital
cameras. Studies have shown they are more cost effective than disposable
batteries. If you must use disposables, check with your trash removal
company about safe disposal options.


If you wonder when you should turn off your personal computer for energy
savings, here are some general guidelines to help you make that decision.

Let your equipment “go to sleep” after a period of inactivity. This is
the single most effective means of saving energy. Though there is a small
surge in energy when a computer starts up, this small amount of energy is
still less than the energy used when a computer is running for long
periods of time. Spending a large portion of time in low-power mode not
only saves energy but helps equipment run cooler and last longer.

One misconception, carried over from the days of older
mainframe computers, is that equipment lasts longer if it is never
turned off. For energy savings and convenience, consider the following

  • Enable the sleep mode on your monitor if you aren’t going to use
    your PC for more than 20 minutes.
  • Switch off both the CPU and monitor if you’re not going to use your PC
    for more than 2 hours.

Make sure your monitors, printers, and other accessories are on a power
strip/surge protector. When this equipment is not in use for extended
periods, switch off the power strip to prevent them from drawing power
even when shut off. If you don’t use a power strip, unplug extra equipment
when it’s not in use.

Most PCs reach the end of their “useful” life due to advances in
technology long before the effects of being switched on and off multiple
times have a negative impact on their service life. The less time a PC is
on, the longer it will “last”. PCs also produce heat, so turning them off
reduces building cooling loads.

ENERGY STAR-labeled computers use 30-65 percent less energy than
computers without this designation, depending on usage. Consider buying a
laptop for your next computer upgrade; laptops use much less energy than
desktop computers.

Sleep Mode and Power Management Features

Many computers available today come with a sleep mode or power
management feature. ENERGY STAR estimates that using these features will
save you up to $30 each year on your electricity bills. Make sure you have
the power-down feature set up on your PC through your operating system
software. This has to be done by you; the power management features
usually are not already enabled when a computer is purchased. Learn how to
activate the power management features on your computer.

ENERGY STAR monitors consume two watts or less in sleep mode. Follow the
instructions for your particular model to ensure power management features
are enabled so your monitor will automatically go into sleep mode after a
period of inactivity. You can save even more by manually turning off your
monitor when you’re not using it; ENERGY STAR qualified monitors consume 1
watt or less when off.

Note that screen savers are not energy savers. Using a screen saver may
in fact use more energy than not using one, and the power-down feature may
not work if you have a screen saver activated. In fact, modern LCD color
monitors do not need screen savers at all.3

Note: While these DoE suggestions are generally applicable to
enterprise, i.e., employee, equipment, employees should consult their IT
Department to determine the enterprise-approved methods for saving energy.

Energy Efficient
Computing Considerations

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In attempting to achieve energy efficient computing, enterprise officials
should consider the following.

Remote Work

Responding to employees’ pleas for more work-life balance – and
accelerated by the COVID-19 pandemic – most enterprises are permitting
their employees – specifically, their “knowledge workers” – to work full-
or part-time from their home or other remote location. While this
metamorphosis has enabled enterprise managers to lower their energy
utilization, home usage has increased. Going forward, enterprise officials
need to cooperate with their remote workers to lower enterprise-related
energy consumption whether in the office or in the home.4

System Development Lifecycle

The computer hardware industry is integrating energy efficiency into its
system development lifecycle (SDLC) in the same way the computer software
industry integrated security into its SDLC. As analysts Rajeev Muralidhar,
Renata Borovica-Gajic, and Rajkumar Buyya observe, “Energy efficiency has
now become a first order design parameter and constraint across the entire
spectrum of computing devices. Many research surveys have gone into
different aspects of energy efficiency techniques implemented in hardware
and micro-architecture across devices, servers, HPC/cloud, data center
systems along with improved software, algorithms, frameworks, and modeling
energy/thermals.”5 At the enterprise level, all lifecycle
processes should incorporate energy efficiency, both computer and


In at least one case, achieving energy efficiency involves avoiding one
problematic application type: cryptocurrency. According to ENERGY STAR,
“Buildings used to house cryptocurrency mining can create a massive strain
on local electricity grids, with a single crypto transaction consuming
more energy than that required to power 6 houses for a day in the US. The
estimated global annual energy consumption of the current cryptocurrency
market is over 68 TWh, equivalent to more than 19 coal fired power plants
operating continuously. Due to the technical nature of blockchain, this
number is projected to grow to 100 TWh annually.”7 Enterprise
officials need to carefully consider the energy and other costs associated
with cryptocurrency before investing in such a resource-intensive

ENERGY STAR Product Finder

ENERGY STAR makes it easy to find an energy-saving computer to meet your
needs. Using the ENERGY STAR product finder, you can select from hundreds
of certified efficient computers from the best, most trusted, and most
popular brands – ike Apple, Dell, HP, Lenovo, and others. Please see
Figure 1.

Figure 1. Sample Product Finder Partial Display

Figure 1. Sample Product Finder Partial Display


In addition to computers, Product Finder can locate other energy
efficient office equipment, including:

  • Imaging equipment
  • Monitors
  • Voice over Internet Protocol (VoIP) phones

Product Finder can also identity energy efficient data center equipment,

  • Uninterruptible power supplies
  • Small network equipment
  • Large network equipment
  • Data center storage
  • Enterprise servers

Enterprise officials need to consult ENERGY STAR and other authoritative market
sources before selecting computing systems or equipment.


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To help create – and cultivate – an energy efficient computing space,
enterprise officials should:

  1. Mandate the procurement of ENERGY STAR-qualified PCs, monitors, and
    other IT equipment.

  2. Configure enterprise equipment with Power Management features enabled
    by default.

  3. Educate employees on the importance of observing energy saving
    protocols. Post these protocols – prominently – in all public areas.

  4. Revamp and revitalize the IT procurement process by incorporating
    energy as a total cost of ownership (TCO) element.

  5. Consider any add-on energy costs when evaluating potential cloud
    sourcing opportunities.

  6. Cooperate with other enterprises of similar size and business
    orientation to identify – and implement – energy efficient computing
    best practices.

  7. Charge the IT Department with the responsibility for establishing and
    achieving aggressive – but reasonable – energy reduction goals.


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