Computing your power savings

, posted: 23-May-2003 21:34

How much power does your computing set-up draw? I was staggered to find my new, highly specified 3GHz PC with 19 inch monitor, laser printer and speakers drew on average almost 2kWh (kilowatt hours) a day.

Looking over the past few power bills, our household goes through about 30kWh/day, about 10kWh more than the average Auckland dwelling. So that means 1/15 of our daily total is used by the computer.

Which got me wondering how much I would save if I switched off my computer gear at the wall instead of leaving it on standby mode overnight. A few calculations later showed I would save 0.4kWh a day, or 1.3 per cent of my daily usage.

Assuming the measured standby consumption figure is representative of other computer set-ups, the average Auckland household would save around 2 per cent of its daily electricity consumption by switching off at the wall.

You would save precious little money, but switching off at the wall really would help to meet the Government's 10 per cent savings goal. To measure the power consumption of my computer set-up, I used a Northern Design MultiCube meter from Auckland firm Carrel and Carrel.

I had to take into account the energy saving technology found in most modern PCs, which puts the PC into "sleep mode" when it's not in use - saving from 70 per cent to 90 per cent. But there is a catch. With energy-saving technology activated, your computer is not properly switched off. Even when you tell it to "shut down" it goes into a deep sleep instead, still drawing power. This is so that users can wake up computers easily, by touching the keyboard, mouse, or so that an incoming fax can be received by a sleeping computer.

So what parts of the system were the power hogs?

Although the laser printer drew only 14W while idle, when printing it gulped down between 250W and 350W. In comparison, the inkjet was a real energy miser, requiring only 25W to print. When turned off with the power button, both printers drew no power.

Next was the computer itself, drawing about 130W depending on use. After that, the monitor was the biggest
electricity consumer at 90W to 110W, depending on the contrast of the screen. With my powered speakers turned on, all the gear drew about 230W to 240W when doing everyday tasks such as word processing, email and browsing the net. Energy consumption jumped to 320W to 340W when playing games.

As the computer drifted off to sleep, total consumption dropped to around 25W once the standby mode kicked in - a saving of around 90 per cent of the in-use consumption.

Allowing for an eight-hour working day, leaving the gear in standby for the rest of the day costs me around 120kW a year. I pay 10.84c a kilowatt hour, so switching off at the wall would save $13 a year.

But if I was using the computer for only two or three hours a day, I'd definitely switch off at the wall. Even
though the money is saved is small (about $20 year) switching off clearly saves energy.

Received wisdom says that leaving electronic gear running prolongs its life, because it is not subject to power
surges and thermal stress caused by cooling down and heating up.

But Roland Feurer, managing director of electronics servicing specialist Futronics, disagrees: "Switch it off when not in use."

His company had found no evidence that the rush of current when powering up as well as heating cold components caused premature failures. Feurer said semiconductors and resistors inside PCs were designed to handle the heat. However, electrolytic capacitors were a different story. Their lifespan was typically 2000 hours to 3000 hours - a figure that went down dramatically with increased temperatures.

Leaving a PC on all year amounts to 8700 hours of use, well beyond how long capacitors last. Another less than obvious consequence of leaving computers on all the time is that they will suck in more dust than when switched off. Computers in standby mode turn off the fans so this applies only to systems left on without
energy saving.

Feurer also said that monitors benefited from being switched off. In standby mode, part of the display tube was kept heated so that the image would appear quickly when the monitor was turned on. This reduced the life of the tube, although not as much as leaving it on all the time with a screen-saver running.

However, David Clark, Computer Products product manager at Sony NZ, said its monitors were designed not to be completely switched off, and in "active off" mode dropped power consumption to less than 2W, without any side-effects from heating the tube.

Feurer agreed that newer monitors used less power to heat the tube, and therefore did not shorten lifespans as much.

If the power crisis comes to a head and electricity is cut to water heaters for 18 hours a day, investing in surge protectors or better yet, an uninterruptible power supply (UPS) is a good idea. Dataguard NZ managing director Paul Jeffries said computers could be protected from power surges and brown-outs for as little as $250 with a UPS. At the minimum, he said, "get surge protectors - they're cheap insurance".

Other related posts:
Zune, a DRM nuisance
NZCS Newsline: Taxing software, Chromebooks, Future of ISPs and Copyright
NZCS Newsline 24

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