CRD or LCD?

CRT or LCD?

I get an email about energy conservation in offices - "Switch off the monitor when not in use", and thought I would get specific information regarding the energy cost savings and pay- off time for a flat screen vs. a CRT monitor.

There are many specific factors that go into calculating this. Among them are:

1. Time Usage – how often your monitor is on (and for a CRT is it asleep or awake?), hours used per day, days usedper year.
2. Energy usage – the wattages of the specific two monitors you wish to compare.
3. Local energy costs – the cost charged per kW by your electric provider:

First, you need to calculate the kW used per year for each monitor. The energy usages can then be converted into costs by multiplying by your energy rate. The difference between the two costs reflects the cost savings you will recoup after using a flat screen (instead of a CRT) for one year. You can apply this annual savings to the price difference between the two models to determine how long it will take to pay off the more expensive flat screen.

The Energy Efficiency and Renewable Energy Network (EREN) is part of the US Dept of Energy. At the EREN website they list the wattage of many appliances - http://www.eren.doe.gov/consumerinfo/refbriefs/ec7.html

http://www.eren.doe.gov/consumerinfo/refbriefs/ec7.html

The wattage of a CRT monitor is listed as 150 watts (awake) or 30 (asleep). This means that in energy use, one hour of awake time => five hours of sleep time for the EPA example monitor.

According to IBM, the T Series flat panel monitors consume 3-4 watts asleep and 30 – 65 watts awake - http://www.pc.ibm.com/us/accessories/access_promo/flatpanel/tour/

Note that the awake energy use changes by a factor of more than 2, depending on screen size. For a flat screen monitor which uses 3.5 watts (asleep) and 50 watts (awake) 1 hour of awake time = 14 hours of sleep time.

For an example solution (for a CRT) see below:

Time Use – hours/day: 6.5 (to account for sleep time)
Time Use – days/year: (52weeks/yr – 2weeks vacation/yr) x (5days/wk) => 250 days/year
Monitor Watts: 150
Cost per kWh: $0.07
[(hours/day) x (days/year) x (watts)] / 1000 watts/kW = annual kWh
consumption (kW) x ($/kWh) = annual energy cost
[(6.5hr/day) x (250days/yr) x (150watts)]/1000 = 243.75 kWh
annual energy consumption (243.75 kWh) x ($0.07/kWh) = $17 per year

A CRT monitor costs $17 per year in electricity. Using the above calculations for a flat screen monitor with the following data:

Time Use – hours/day: 6.2 (to account for sleep time)
Time Use – days/year: (52weeks/yr – 2weeks vacation/yr) x (5days/wk) => 250 days/year> Monitor Watts: 50
Cost per kWh: $0.07

A flat panel monitor costs $5.40 per year electricity.

To determine your annual energy usage, use the wattage values printed on the back/bottom of the two monitors you are comparing. To determine the Time Usage for a CRT that goes to sleep, use an average value of time based on the % time the monitor is awake/asleep.

Additional Information ->> Many resources can be found where the energy efficiency of flat screen monitors is touted. Several of these sites are:

UC Irvine News, March 14, 2001 ->
http://www.today.uci.edu/ucinews/0314f4.html

National Renewable Energy Laboratory -> http://www.nrel.gov/sustainable_nrel/energy_saving.html

While the EPA Monitor Power Management Calculator is helpful in> computing cost savings on the basis of certain criteria, this calculation does not allow you to calculate costs based on monitor type.

http://yosemite1.epa.gov/Estar/consumers.nsf/content/powercalculator.htm

I used the following search terms: flat, screen, panel, monitor, energy use, efficiency, watts, utility, cost, electricity.

One more article is : http://www.thehindubusinessline.com/2006/07/11/stories/2006071102140400.htm>>>


Another article on this is:
http://savingenergy.wordpress.com/2006/11/21/saving-energy-one-monitor-at-a-time/