It's been done. One place I worked, we were replacing a mainframe, The new one was a CMOS job, compared to the old ECL hardware it used much less power. The prime selling point was that it would save the organisation £250k annually in power consumption. (N.B. This was back in the nineties, when by comparison with today, electricity was practically free).

In it went, out came half the chillers that had been necessary to keep the old unit from frying itself. The power savings were, indeed, impressive - until it was pointed out that the swap-out had been done during the summer - during the winter the excess heat had been channeled upstairs to help warm the IT centre which was directly above it.