I have a small computer datacenter that consumes about 25kw. Airconditioning cools it to about 25C.

When renewing the airconditioning, I suggested replacing it with air heat pumps for 'green' cooling, so the heat could be used to heat water for radiator space eating or hot water heating. I was hit by a barrage of reasons why this wouldn't work, although my calculations suggest it would. However, I can't find any suppliers for this, which suggests I am wrong.

Would it work, and if not, why not?

I'm researching this for my company, in the name of 'green IT'.  Is there a tipping point?  A number of copies at which it becomes better to use one of the methods? 

In my office we fill out a time sheet each week, which has a yellow background and must be printed out on a laser printer.  I print mine in colour, but many colleagues print the sheet in black and white so the background colour comes out light grey.  They claim this is more environmentally friendly.  But I say there's no evidence that black ink has a higher environmental cost than yellow ink, so it makes no difference.  Who is right?