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Mobile Wireless Computer Labs - The Energy Efficient Alternative
The use of computers is rapidly infiltrating the education sector, playing a key role in shaping curricula and influencing pedagogy. It is becoming increasingly common for students to be engaged in active and cooperative learning and increasingly imperative that this learning occur continuously through the support of modern technology. One-to-one computer initiatives are on the rise and schools worldwide are seeking durable, easy to integrate computing solutions that will enable them to create effective and effcient e-Learning environments. Alongside this trend, is of course the prevalent challenge of establishing a more sustainable foundation for technology integration, and therefore, investing in technology that not only meets classroom needs within budget requirements, but is also eco-friendly.
Selecting a technology solution that will yield desired outcomes for instruction and learning brings to bear several factos for consideration. Notably, and in light of the growing trend towards "green" technologies, energy consumption (power efficiency and its impact on performance), and total cost of ownership is at the forefront. |
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Comparing Energy Consumption
The performance of desktop PCs has improved considerably over many years, with processors increasing from 6MHz to 2.5MHz1. Yet, the energy consumed by a typical desktop PC still ooutweights that of a laptop computer. Compare 65 - 250 watts consumbed by the average desktop PC with 15-45 wats typically used by a laptop computer2; on average, a typical laptop consumes 1/5 to 1/7 the power of a typical desktop PC3. |
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The disparity is largely a result of energy-efficient features that have become trademarks of today's laptop computers:
| Energy Efficient Displays |
A typical 14" LCD screen accounts for 33% of overall energy consumption, while a typical 17" desktop PC monitor accounts for more than half of the energy use of a typical computer setup.4
Many laptop computers have liquid crystal displays (LCDs), while most PC monitors use cathode ray tube (CRT) technology; color LCD monitors use only 10% to 20% as much power per square inch as color CRT monitors. |
| Power Supply Efficiency |
External power supplies that provide adequate power to run a laptop computer are more efficient and result in very little power supply lost.
Power supply accounts for nearly 1/4 of the energy use of a typical desktop PC.5 |
| Operational Mode Efficiency |
A typical laptop powers down and reduces energy consumption when not in use. In standby, sleep an didle modes, the amount of power used is greater for desktop PCs (a maximum of 2W while in standby, 4W in sleep, and 50W in idle comared to 1W in standy, 1.7W in sleep, and 14W in idle for laptop computers).6 |
| Power Managment |
Laptop manufacturers are continually developing new power management technologies to reduce energy consumption and increase overall efficiency. |
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| The afore-mentioned features point toward the environmental friendliness of laptop computers and, in turn, of mobile laptop computer labs. Consider a typical computer lab with 30-32 computers, enough to provide students in an average size classroom with one-to-one access. A fixed desktop lab with 32 units (using on average 130 watts each) will utilize approximately 4,160 watts, whereas a mobile laptop lab with 32 uints (using on average 30 watts each) will utilize approximately 960 watts. Even when power consuming AC adapters and peripherals are added, the amount of energy utilized by mobile computer labs is still considerably less than that of desktop computer labs (see reference note below).7 |
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Total Cost of Ownership
The energy savings of laptop computers are readily apparent, yet fitting a technology solution into a pre-determined budget is typically of utmost concern for many schools. Given that the initial cost of a PC workstation is less than that of a mobile laptop computer, implementing fixed desktop computer labs appears at first glance to make the most of a school's purchasing dollars; however, total cost of ownership is reflective of much more than just the cost of the computer system - energy use is a key determinant of the costs that will be incurred over the longer term.
On average, each desktop computer draws approximately 2 amps of electricity per hour of use. In a lab of 32 computers that are used an average of 6 hours per day, this amounts to 384 amps of 42.24 kilowatt-hours (kwh) of electricity. At the average price of 8.9 cents per kilowatt hour for electricity (as indicated by the Energy Information Administration), mobile laptop labs drawing less energy will result in cost savings in both the short and long-term.
The following chart compares electrical and cost savings of a typical desktop lab with an EarthWalk SmartCart™ wireless mobile computer lab. The SmartCart™ mobile lab draws only 8.3 amps or .91 kwh of electricity to charge the entire unit. The ratio of charging to battery life is approximately 1:2; meaning that the computers can be operated for twice as long as they are charged. A SmartCart™ would need to be charged for 3 hours, using 2.74 kwh of electricity per day, to provide for 6 hours of use. The unique power management capabilities of the SmartCart™ to conserve electricity results in a savings of approximately $633.00 in the first year, and $1,900.00 over a 3 year period. |
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Electrical Costs Comparison |
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Amps/ hour |
Kilowatts/ hour (kwh) |
kwh per day
6 hrs. for Desktop Lab
3 hrs. for Mobile Lab |
Total Daily Cost @ 8.90 cents/ kwh |
Cost for 180 Day School Year |
Cost Over 3 Years |
Fixed Lab |
64 |
7.04 |
42.24 |
$3.76 |
$676.80 |
$2,030.40 |
Mobile Wireless Lab |
8.3 |
0.913 |
2.74 |
$0.24 |
$43.20 |
$129.60 |
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In addition to energy utilization, the desktop computer lab model of a computer learning environment requires considerable electrical infrastructure — including dedicated wiring and circuitry as well as cooling system upgrades — that contribute to both short and long-term underlying costs.
The “Taking TCO to the Classroom: A School Administrator’s Guide to Planning for the
Total Cost of New Technology” report from the Consortium for School Networking (CoSN) provides several studies from organizations who have researched infrastructure costs in the
United States. A frequently cited study by McKinsey & Company, Inc. (1995), estimates that 65% of American Schools are more than 35 years old and have not undergone the major renovations required to support today’s technology. The consultants in this study projected that 23% of the nation’s schools would require an upgrade of their electrical system and another 4%, improvements to their heating, ventilation and air-conditioning (HVAC) systems. It estimated that the average school would spend $240,000 on electrical upgrades and $31,000 on HVAC.
Another study for the Council of Educational Facility Planners International, “Implementation Costs for Educational Technology Systems”8 found that it cost approximately $3,000 per classroom equivalent in renovation-modernization projects. That cost included one additional 20 amp 100VAC circuit, six empty data box drops and six duplex outlets. The study also concluded that additional electrical service would cost a minimum of $50,000. With a fixed desktop computer lab housing 32 units, a minimum of 16 outlets (2 sockets per outlet) would be needed to power the computers, requiring additional wiring in a typical space. Wiring would need to be further expanded to allow for the use of other electronic devices such as printers, scanners, projectors, and other peripherals.
These studies demonstrate that although variable, the cost of establishing the infrastructure for connectivity and electricity for a dedicated computer lab is substantial. With one computer per child initiatives becoming a growing trend, deploying low-cost solutions with maximum efficiency is increasingly important.
1Intel, PC Energy-Efficiency Trends and Technologies
2http://michaelbluejay.com/electricity/computers.html
3Intel, PC Energy-Efficiency Trends and Technologies
4ibid
5ibid
6http://compreviews.about.com/od/general/a/EnergyStarPC.htm
7Although laptops consume less energy than desktop PCs, electrical hazards such as the overloading of circuits and considerable power utilized by AC adapters remain a concern in mobile lab environments where more than twenty laptops are in operation. Part II addresses innovations in eco-friendly power management that eliminate the hazards associated with charging a large number of laptops in an e-Learning environment.
8http://www.cefpi.org/issue7.html
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