I began the work for the day with contracting matters. Apparently a contract had almost ran out the approved value so it is my duty to identify, justify, and get ratification for a new contract value. Yes indeed, I am a qualified Contracting engineer. But I lack the depth of the laws and procurement part of the contracting. I’m just good at the surface. Those two roles are integral for a contract to be in place, but it’s not like I’ll jump over to the supply chain or the legal band soon, right?


The energy-saving initiative at work posted this on the board the other day:

If you turn off the PC overnight, you’ll save enough the carbon emission equivalent to power up 2 televisions for a year.

If 10,000 PCs are turned off overnight, between us, we’ll save enough carbon emission equivalent to drive to the moon and back 4 times!

I looked at the first and pondered, OK, that’s fine. 1 PC consumption for 12 standby hours could be the same electricity generation required for 2 TV set for a year. The PC must have been the power-hungriest Pentium 4, one of the most inefficient of the sorts with the cooling vent partially blocked or something. And the TV set must have been the most energy-efficient, award-winning Energy star compliant LED type, the ones about an inch thick, endorsed by by both WHO and the United Nation.

But when I looked at the second – I found that a little hard to swallow. Maybe it’s just me.

So I did a little fact-finding.

Check your facts!

According to Sightline institute (non-profit), CO2 emission for an average sedan is 1.10 lbs/ passenger-mile. Assume this is one passenger going to the moon and back so the emission equivalent is 1.10lbs/mile.


Earth’s radius is 6367.5km. Moon’s radius is 1737.5km. The mean distance between center earth to center moon is 384,403km. So the distance between earth surface and moon surface is:

Dmoon-earth = 384,403 km – 6367.5km – 1737.5 km = 376,298 km

= 233,821 miles#

So driving to the moon and back four times equals

8 . Dmoon-earth = 8 x 233,821 miles      = 1,870,565 miles

The carbon emission equivalent is then

1.10lbs/mile x 1,870,565 miles                  = 2,057,621 lbs

A Dell Optiplex GX620 on the other hand consumes 220W power at max, at about 88% efficiency (per Dell’s published technical book, Energy Star compliance). Assuming that without much activity by leaving the PC to standby overnight (fan, HD and minimum power to motherboard), the PC still operates at about half of 220W on the high side (a factor of 0.5)

The estimated actual power rating is then:

0.5 x 220W    = 110W

According to the Department of Energy’s Energy Information Administration, on average, electricity sources emit 1.297 lbs CO2 per kWh (0.0005883 metric tons CO2 per kWh). State CO2 emissions per kWh may vary greatly in accordance with the amount of clean energy in the energy supply (Vermont, Idaho: .03 lbs/kWh; North Dakota: 2.24 lbs/kWh).

So if 10,000 of you turn off the PC for 12 hours until the morning, the resultant power consumption during that period would be:

10,000 x 110W x 12 h                 = 13,200,000 Wh         = 13,200 kWh

1.297lbs CO2 /kWh x 13,200    = 17,120 lbs!

Even by using more conservative numbers, the result is

10,000 x 0.220kW x 12 h x 2.24 lbs/kWh = 59,136 lbs!

I ran through the above with a friend next door in case I missed out anything and submitted it to the energy-saving initiative team. In my e-mail, I asked, “So what are your sources for the figures? What is your basis?”