Digressing a little our airline had a distributed system of high pressure air hoses installed underground at each gate of our 'hottest hub'
These were accessed through a manhole type cover and connected to the aircraft, we used them to run packs and start engines with an inop APU.
It worked okay if not too many aircraft were connected (not nearly as effective as external conditioned air) but if every gate was occupied using the system pressure dropped and it lost its effectiveness.