Great picture, I just thought of this, but the vents outside the building were air intakes for the compressors. One thing that these compressors didn’t have is aftercoolers (allot of heat is generated compressing air) so the cooler the intake air the better. MTU learned this lesson the hard way in the school mine, the old electric compressor would melt the gaskets in the victaulic airlines because of the heat generated and the lack of an after cooler.

Joe - Air intakes makes sense (I don’t even know what I was thinking originally, since what would steam engines need with a vent?). However, inside I don’t remember seeing any direct connection between the vent for the south compressor and the compressor itself. (this would be on the left side of the panoramic) Perhaps it ran underground? Or perhaps its just simply missing.

If you look at the compressors, on the ends closest to the door you enetered from you can see the manifold for the compressor, and the intake line is missing from both of these compressors (you can kinda see the flange on the north compressor in the picture), how they actually connected to the compressor is a good question, I dont remember from when I was in the building (no snow). I would have thought they would come into the manifold straight so you would only have one elbow before the manifold, but I could be wrong.