AC

As someone pointed out, it is very possible to lower AC requirements - we've done so ourselves, reprogramming the AC unit in our server room to less than half the previous output.

The other factor with AC is quite simply less machines = less heat = less power required by AC. Yes the one VM does require more power than a single server, so it's not (in our case) 1/4 of the heat output, it was more like 3/4.. but that was still a significant drop.

Generating 25% less heat combined with reducing the output of the AC to about 1/2 the previous room coverage = a nice saving on the electricity bill. I'm only guessing here, but I reckon a lower electricity bill is quite a good indicator that our setup is greenerer that it was before.

*greenerer is a technical term I'm lead to believe, meaning more trees for George Bush to stand next to in order to look like an environmentally friendly prez.