The steam would have filled the radiators under pressure and the heat would have also traveled via conduction. As you can see the pipes were painted not insulated so they were meant to give off their heat as well as the radiators.
The condensate drain must have been done manually unless something like the old pressure valves that whistled has been broken off. Something that big I would expect the school maintenance guy had to remove the plug at the end of each winter and maybe even have the system blown out with air to make sure no water sat. Having water sit in the bottom of radiators or any part of a steam heat system severely lowers its efficiency.
Authoguy,
I deduce that is not Asbestos. If it were period asbestos in that place it would have been covered in canvas and mastic. You can see the pieces are not covered in canvas as there would be signs of it.
The post Asbestos standard would be to use calcium silicate. That is what those pieces look like. They might still use canvas and mastic but since there is no sign of it I figure they used metal which was probably .032 paper backed aluminum sheets. It's probably missing because a scrapper took it. The insulation must have been taped in place as I do not see the more usual wires to tie it on. The insulator also was probably not professionally trained as there is no staggering of the joints. so there would be hot spots at the end of each section. It may be that the insulation was to prevent people from touching hot pipes (it appears to stop at the height most people can reach easily) not to save the heat since there is no sign of enough to have covered the pipe all the way up.
The bowling alley and other such amenities were there for the residents to get activity and socialising. The cost once installed would just be maintenance which as you see was done well.
In the 70's as story after story of hideous abuses were reported and factors like people with mental illness who could actually live on their own being among them the nation pretty much emptied most of its psychiatric hospitals and the former residents now live with family or on their own with subsidies or on the streets as homeless.
I do not know that is how this place came to be empty, I haven't read Mott's whole story on it yet. But in general that is why bowling alleys and other things in these places get left to decay.