Computer Labs and Electricity Usage

The Office of the Physical Plant tested a 3.6 ghz P4 computer running Windows XP with a 17" LCD flat screen monitor and found that the system used the following:
Computer On and at Idle, Monitor On     - 145 watts
Computer On, Screen Saver Active         - 150 watts
Computer On, Monitor is Sleep Mode      - 105 watts
Computer On, Monitor Off                       - 105 watts

Personal Computer and Monitor:

145 watts

On for 24 hours a day 365 days a year

Annual energy consumption = 145 watts (1kWh/1000Wh) x 24 hours x 365 day = 1,270.2kWh / year

This is when the computer is on and the screen saver is active (which is the state of the majority of the computers in Bouke computer labs).

The cost of running one of these computers for 24 hours a day if 1 kWh costs $ 0.10

Cost = 1,270.2kWh x $ (0.10/kWH) = $ 127.02/year for 1 personal computer

Remember that cost because there are some computer labs in Bouke with 80 to 90 computers all costing the university $127.02/yr to run. (There are at least several hundred computers running simultaneously throughout the entire building).


If the computers were turned off completely it would still be consuming some energy called flea energy (about 2.3 Watts). Monitors consume 0 watts when off.

Total watts: 0W + 2.3 W = 2.3 watts

Assuming we shut off computers for 8 hours a day (midnight, which is when the labs close, to 8:00 AM, when the classrooms open)

Annual energy consumption = consumption when on + consumption when off
Annual energy consumption = (145 watts (1kWh/1000Wh) x 16 hours x 365 day) + (2.3 watts 1kWh/1000Wh x 8 hours x 365 days)
Annual energy consumption = 846.8 kWh + 6.716 kWh
Annual energy consumption = 853.516 kWh / year

Cost = 853.516 kWh / year x $ 0.10/kWh = $ 85.35/year for 1 personal computer


Thus, if the computers were completely shut down from 12AM to 8AM the cost would decrease by $41.67 / year for each computer. While this might not seem like too much, taken over the more than 200 odd computers in the building, this figure becomes a savings of nearly $10,000 per year.

So ask yourself, what is your screensaver saving? It certainly isn't your money in energy usagage...


A typical computer power supply.