I've just been looking at this. According to the major equipment suppliers, if you recover the energy from 4 to 4.5 % evaporation, you can preheat the wort from the lauter tun from about 75 C to 92 to 94, dependent upon plant efficiency. If you work out the cost of all the pumps, tanks, heat exchangers, maintenance, space etc, you will probably find the figures don't add up.
You can also reduce energy consumption by installing vapour recompression plants, but this definitely won't pay for a micro
If you recover the energy from the hot wort on transfer to the FV, you should get about 1.1 hl hot water at circ 85 C for every hl wort you chill down, dependant upon the cold water temperature and the cols wort out temperature. This is probably worth saving because you can use the water for mashing in, sparging, and CIP