Energy Consumption of a Desktop Computer

Some people have the habit of keeping the computer switch on for days, specially at the working place. Let's analyse the energy consumption of a desktop computer under various scenarios.

Below calculations are based on the computer I use at work place. It consumes ~70W when in operation. LCD monitor contributes 25W to it.

Assume your team size is 5 (each member has his/her own computer).

Average work hours per day = 11hrs (worst case)
Work hours per week per member = 11hrs * 5 = 55hrs
Total energy requirement per week per member = 55hrs * 70W = 3,850 Wh
Total energy requirement of all the members = 3850Wh * 5 = 19,250Wh

Scenario 1: Member "A" keeps his/her computer switch on for consecutive 2 days. (from [day1] 8AM to [day2] 5PM)

A's consumption = (33hrs  + 11hrs * 3) * 70W = 4,620Wh
Energy consumption of other members = 3,850Wh * 4 = 15,400Wh
Total consumption of all the members = 4,620Wh + 15,400Wh = 20,020Wh
Energy wastage = 20,020 - 19,250 = 770Wh (4%)

Scenario 2: Member "A" keeps his/her computer switch on for consecutive 3 days. (from [day1] 8AM to [day3] 5PM)

A's consumption = (57hrs  + 11hrs * 3) * 70W = 6,300Wh
Energy consumption of other members = 3,850Wh * 4 = 15,400Wh
Total consumption of all the members =  6,300Wh  + 15,400Wh = 21,700Wh
Energy wastage = 21,700 - 19,250 = 2,450Wh (13%)

Scenario 3: Members "A", "B" keep his/her computer switch on for consecutive 3 days. (from [day1] 8AM to [day3] 5PM)

(A+B)'s consumption = 2 * (57hrs  + 11hrs * 3) * 70W = 12,600Wh
Energy consumption of other members = 3,850Wh * 3 = 11,550Wh
Total consumption of all the members =    12,600Wh  + 11,550Wh = 24,150Wh
Energy wastage = 24,150 - 19,250 = 4,900Wh (25%)


I think you can understand these numbers. At least the percent wastage. Sadly, this is the behavior of average worker! Some workers even have the habit of keeping the computer switched on throughout the week. Monday morning switches on and Friday afternoon switches off!

There may be a requirement to keep the machine on while you are not at work. But those situations are exceptional and rather rare.

Do your bit for the country! Do your bit for the environment! Please make sure you turn off your computer when you leave the office!

Does bulk ironing save energy?

Recently one of my friends suggested that we may not be saving much energy if we iron clothes more than one at a time compared to ironing clothes separately. His argument was, unlike the old irons new steam irons might have designed to save energy by reducing the time it takes for preheating.

This sparked me to do another experiment nearly a year after to the last post :) and here it goes...

Iron I used

Make:	Morphy Richards
Model:	Comfigrip (40715)
Watts:	2020W-2200W

Below table shows the experiment results.

From the above statistics,
for 1 piece, it consumes 0.09 kWh.
for 5 pieces, it consumes 0.28 kWh.

Below table summarizes power consumption to iron 20 pcs.

That is, if 10,000 people iron a week's clothes at once we can save 81,600 kWh of energy a year. It is equivalent to stopping release of 2907.24 kg of carbon-dioxide in to atmosphere.

Can't you still figure out how much is this 2907.24 kg?

It is equivalent to carbon-dioxide produced by a Toyota corolla (2002) when it goes 17,000 kilometers of distance a year and this is really big!

Next time please iron more than one cloth at a time. It saves you money and make the air we intake clean.

References

1 - Relative CO2 emission from various fuels

2 - Carbon Inventory

3 - Car emissions

CFL Lifetime

CFL nominal rated lifetime is ~8000 hrs. But this will be affected mainly by operating voltage, manufacturing defects, exposure to voltage spikes, mechanical shock, frequency of cycling on and off, lamp orientation, and ambient operating temperature, among other factors.^[1] Out of the above causes, at least "frequency of cycling on and off" and "lamp orientation" can be contrlled by the user.

I do not have much information about how "lamp orientation" will affect lifetime of CFL.

But according to energysavers.gov, if you frequently on/off CFL its lifespan can be reduced to close to that of incandescent light. energystar.gov suggests if you leave the room for less than 15 minutes, better to switch on the CFL. In other words, switch off CFL when you are out for more than 15 minutes. Therefore, using CFLs in bathroom may not be a wise idea becasue, though it gives a reduced light bill, CFL replecement cost will tradeoff the benefits you get from a reduced light bill.

Next time, wait 15 mins before turning it off again... :)

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1 - CFL#Lifespan