After the Richard Stallman lecture last night I ended up talking to the CTO of One Planet Computing. They are specialists in green computing and even provide people like Cutter with some of their technologies. Anyway, to cut a long story short, they have a rather natty carbon calculator here: basic carbon calculator and there is alos an advance calculator and one that compares fat client and thin client computers.
Calculating CO2 emissions is quite easy, you just get KWh and multiply by 0.544.
I think I agree with their PC power calculator, but I don't quite get the 'Virtual desktop comparison' one, it appears to leave out some factors.
For example, the latest BroadLeaf Energy Efficient Core i7 Desktop idles at 16W and has an average consumption of 20W, compare in a thin client and most of the time these use 15W or so.
Theory would suggest the thin Client is better right now right? Wrong.
However, the servers required to run the Virtual Desktops haven't been considered here, which will have a considerable power consumption of several hundred Watts, and support maybe 50 respectable simultaneous multimedia users. This server will be in a server room, running 24/7, which will likely mean it's air conditioned (think double your power consumption here unless you've done some air containment in your server room). This server isn't running the 2000 hours per year + power policy time (power policy time is the time taken for your power management policy to kick in), it's running 8760 hours per year, about 4 times as much.
In addition there will be the fact that Thin clients can't generally be power managed as effectively as PC's and the Thin client's power policy time is likely much more.
I also don't advocate turning old computers into thin clients; it might seam like an admirable thing to do but it means your thin client is going to be using 50W when on, 46W in 'sleep' and probably 6W when off. Actually recycling these old machines is so good these days not much is going to see a landfill, manufacturing and embedded CO2 in a new PC or thin client stars from about 100KG and the money saved by the school in electricity would far outweigh the cost of a cheap thin client.
In order to be legal in the EU, modern computers and thin clients need to consume less than 1.7W in off state, there is no limit on 'sleep' right now. A typical energy efficient PC would use less than 3W on sleep.
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