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Energy-efficient PC/workstations

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MECH425 Project Page in Progress
This page is a project page in progress by students in Mech425. Please refrain from making edits unless you are a member of the project team, but feel free to make comments using the discussion tab. Check back for the finished version on February 7, 2010.

Conserving Energy at Your PC/Workstation

There are many items at a typical office workstation that consume unnecessary power. Many aspects of a PC/workstation were considered, including processors, video cards, and fans. It was found that only three sources of excess power consumption were identified as cost effective to replace with energy efficient models. The provided ECM (Energy Conservation Measure) files indicate steps that can be taken to reduce a company's utilities expenditures and carbon emissions. The economic benefits of these energy efficient products are emphasized in the analysis.

Each energy conservation method has been kept separate for simplicity. The monitor and power supply ECMs can be used in conjunction with one another as well as the monitors and laptops ECM, however, the Laptop and power supply ECMs are mutually exclusive because replacing desktops with laptops eliminates the need for desktop power supplies. For this reason the ECMs were kept separate.

If your company has old and inefficient monitors in use, please see the Monitors section below.

If your company is looking to replace their current computers, or would benefit from the increased productivity of a notebook or netbook computer, please see the Laptops section below.

If your company has desktop computers, which do not use energy efficient power supplies, please see the Power Supply section below.


Monitors use the majority of the power required to run a computer workstation. Turning off the monitor, or placing the computer in sleep mode can drastically reduce the required electricity. Cathode Ray Tube (CRT) monitors use, on average, 73 Watts while Liquid Crystal Display (LCD) monitors use 41 Watts. Energy Star LCD monitors, however, use only 28 Watts. Most Energy Star monitors, under 20 inches, can be paid off in under 5 years fom energy savings alone. When switching from monitors that are not Energy Star certified, the payback time can be further reduced by enabling power saving functions on your computer. This will turn the monitor off or switch into sleep mode when the monitor is not in use. This spreadsheet compares Energy Star monitors currently available online directly from the manufacturer and often include discounts for businesses.

Monitors ECM

This ECM details the savings generated by reducing electricity consumption associated with changing your current monitor to a new energy efficient model. The ECM contains many different models of varying to accommodate specific needs. The Economic and emissions savings are detailed.

ECM Inputs:

  • Current monitor size
  • Hours the monitor is currently on, in sleep mode and off
  • Proposed hours the monitor will be on, in sleep mode and off
  • Power consumption of the monitor while on, sleep and off
  • Number of Monitors
  • Working days per year

ECM Assumptions:

  • Carbon, SO2, and Nox emissions per kWh
  • Cost of electricity
  • Inflation of electricity

ECM File:

Click here to download the Energy Efficient Monitors ECM

File:ECM for Energy Star Monitors.xls


In general, desktop computers use much more energy than notebooks or netbooks. Even an Energy Star desktop can use about 160kWh in a year, while the average Energy Star notebook uses only 37kWh. Many offices may be wary of switching to laptops simply because they are accustomed to having a desktop with a big screen and external hardware. This is overcome by using a laptop docking station. The user's monitor, keyboard, mouse, printer etc. can easily be connected to the docking station. The laptop can be easily connected or disconnected from the docking station allowing for no change in workstation operation. The docking station allows for ease of integration while drawing significantly less power. Laptops also provide the added benefit of allowing employees to take work home or on the road, increasing productivity and adding value to your company.

Laptops ECM

The Replacement of Desktop Computers with Energy Efficient Laptops ECM covers three specific cases:

  • The company is planning to replace some of their current computers with similar models (recommend an extra investment for energy efficient models)
  • The company is planning to replace all of their computers with similar models (recommend an extra investment for energy efficient models)
  • The company is not planning on replacing any computers (all cash flows from energy savings and increase in productivity)

ECM Inputs:

  • Number of working weeks in a year the company has
  • Value of an hours work done by an employee at home
  • Number of hours a week they expect an employee to work at home per laptop computer
  • Cost of one of their current PCs
  • Number of computers the company uses
  • Hours per day the computers are in sleep mode (including overnight)
  • Hours per day the computers are on and being used
  • Days in a week that the computers are used
  • Average power used by each computer while on and in use
  • Average power used by each computer while in sleep mode
  • Number of computers the company wishes to replace
  • Cost of a new, energy efficient laptop (some examples provided in the ECM)
  • Number of docking stations the company wishes to purchase
  • Cost of a docking station (some examples provided in the ECM)
  • Average power consumption of energy efficient laptop while on (some examples provided in the ECM)
  • Average power consumption of energy efficient laptop while in sleep mode (some examples provided in the ECM)

ECM Assumptions:

  • Carbon, SO2 and Nox emissions per kWh
  • Cost of electricity per kWh
  • Inflation in Canada

ECM File:

Click here to download Energy Efficient Laptop ECM

File:Energy Efficient Laptop ECM.xls

Power Supplies

Most power supplies installed in a desktop computer consume a significant amount of power and are only about 60-65% efficient. Many energy efficient power supplies are now available for under $80 and can increase efficiency to over 80%. Replacing the power supply on a desktop computer is an easy task for an IT department and can save money on electricity.

Power Supply ECM

This ECM can be used to determine the cost and energy savings derived from replacing a computer’s old power supply with a new energy efficient power supply. It will also calculate carbon, SO2 and NOx emissions savings by switching the power supply on your desktop computer. The file contains information on many energy efficient power supplies.

ECM Inputs:

  • Number of computers at the company
  • Current computer power rating
  • Hours a day the computer is in use
  • Current power supply efficiency

ECM Assumptions:

  • Working days in a year
  • Cost of electricity
  • Inflation in Canada
  • Carbon, SO2 and Nox emissions per kWh

ECM File:

Click here to download the Power Supply ECM

File:Power Supply ECM.xls