Heating, Cooling and HVAC

If you are putting in a home office. Do your computers and fax machines really use too much energy?

If you use a PC built before 1994, it can use around 200 W, and a laser printer can use around 100 W; if you leave this on 24 hours per day this can add up to over $200 a year. But many PCs, monitors and printers built since 1995 have “ENERGY STAR” capabilities, which save a lot of energy when you enable this feature.

Should you leave your home computer on all the time, or turn it off when not in use?

Only you can decide whether to leave your computer on, or turn it off. There are reasons for each strategy. The typical computer draws around 100 Watts, or 2.4 kWh/day. Multiply this by your electricity rate per kWh to come up with the cost per day. Leaving a typical computer on all the time would cost about 21¢/day (2.4 kWh * 8.6¢/kWh). This may not seem like much but it adds up to close to $75/year. If you don’t have any particular reason to leave your computer on, that money would be needlessly spent.

There are reasons to leave your computer running 24 hours per day. One is if you use it as a web server, or if you use it to receive faxes 24 hrs/day, for your at-home business. If these do not apply to your computer, then it makes sense to turn off your computer when it is not in use.

Don’t worry about wear on the computer from turning it on and off repeatedly. This was once a problem in the early days of personal computers, but now your computer undergoes more wear from running constantly than from being turned off when not in use. If you do leave it on, try to have an Energy Star unit. There are after market devices to turn your computer after extended periods of inactivity.

If you have been using a screen saver, you might reconsider. It’s fun to look at, but you are paying for that entertainment.

The 8500 has a maximum power consumption of about 200 W, and the monitor an additional 100 W. (The *maximum* the 8500 box itself can draw is 200 W, if there are a lot of high-powered cards installed; usually it uses much less.) In “sleep” mode, it draws less (about 15 W).

With this information, you can figure out that the worst-case consumption should be something like 300 W x 24hr/day = 7,200 Whr/day, or 7.2 kWh. If your electricity is 10¢/kWh, this costs a maximum of 72¢/day, or $21/month.

Do you really think your answering machine uses more electricity than your computer?

Surprising though it may seem, most answering machines use more energy than most computers. Here’s how it breaks down:

………………………Answering Machine…………………. ……………………………Computer
Energy Consumption………… 5 Watts ……………………………………………. 200 - 250 Watts
Typical………………………. Usage 8760 hrs (always on)……… 10.5 hrs/month or 126 hrs/yr
Annual Consumption………….. 43.8 kWh/yr……………………… 25 to 32 kWh/yr

The equation to derive the annual consumption is:

Annual consumption = Energy Consumption (Watts) 1 kWh per 1000 Watts Usage per year

Obviously there are assumptions about typical usage and typical consumption. The numbers used in the Home Energy Advisor are national average numbers, which may not accurately reflect your particular use and computer system. If you work at home and use your computer every day, the module will not portray the energy consumed by your computer accurately.

This type of assumption is present throughout the Home Energy Advisor for end-uses that do not typically result in a significant portion of household energy consumption. Simplifications like this one shorten the time required to enter inputs, without greatly reducing the accuracy of the overall estimates.

Source:Home Energy Saver - lbl.gov