Taking your idea a step further... When I did an internship at an architecture studio, the design of the central plants that provide hot/cold water/air to their surrounding buildings would use the exhaust heat of say, a water chiller for the air conditioning unit, to help heat the hot water flow, taking load off of the water heaters. In one case, they had enough "excess" heat available from doing this that a school got a heated pool for "free."

You could do the same thing with the exhaust heat from the compressor to heat the restroom water for the data center's bathrooms.

Not exactly super exciting to most, but for whatever reason I think stuff like this is the coolest thing ever.