Do 25 MW turbo compressor units need to be installed in building or outdoors?

Answer 1

They need to be indoor if the equipment needs to avoid environmental extremes: humidity, acidity, coldness, hotness, radiation, etc… Otherwise they should be outdoor.

In contrast, they need to be outdoor if, say, they burn too much air and produce too much noise and deadly gases (powered by a combustion engine), or are not economically affordable indoor. For example a portion of that 25MW will turn into heat (you cannot have a 100% efficient motor and a 100% heatless compressor); and that heat, in turn, needs to be pumped out by an air conditioning system which runs at a net heat-pump efficiency of much less than 100%.