We have two like that here in my building, one larger than the other. Both return air fans. One on a freq drive, the other not. Showed the bigger one to my wife one time during a tour and she freaked. That and the fact that I can walk inside the return side of the air handler that return fan is attached to (I'm 6' 4") with tons of headroom to spare had her kind of spooked. Funny how the same piece of equipment affects people different ways.
Electricity makes refrigeration happen.
Refrigeration makes the HVAC psychrometric process happen.
HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.
A building is NOT beautiful unless it is also comfortable.
Thats a baby you should see the ones you can move the whole family into. Some the unit was installed then the concrete walls. Had to do shafts and bearings several times on these types one time the large unit was suspended in the air in the mechanical shaft what fun that was. $ Would be happy to do yours just send a email
once seen an air handler about that size had an inhouse guy at the mall open the door without turning off the disconnect oops sucked in his little craftsman rollaway toolbox come to find out he had earlier in the week jumped out the door saftey to enable it to run$$$$$$ big dollar fix