This bank of transformers is being used to power several VAV box controllers. One of many VAV boxes are powered by one of these transformers. In most VAV box applications, the power for the control system is at the box and an properly sized transformer for VA load is used to power the controller. In this application, the VAV boxeswere not fan powered and line voltage was not available at the boxes. So a central transformer bank was used and wire for control power was pulled to each VAV box.
Using the manufacturers rating of the DDC controller and the power needed to drive all the actuators which is also a VA rating on the actuators, the entire load was calculated and the appropriately sized transformers were used. If the load demand for the transformer exceeds the transformers VA rating the controllers may not work properly and the transformer will over heat and eventually fail. With the number of transformers in this panel a small panel fan was necessary to remove the heat from inside the panel. Transformers generate a lot of heat and it is important to have a method to keep them cooler.
Your Resource for HVAC Control Transformer Information
These control panels offer resistance to inclement weather. They house the controllers for two small chillers and two air handlers. The chillers provide chilled water for air conditioning to the air handlers. The controllers offer energy management for the air conditioning system. The controllers were mounted outside for a few reasons. The main reason was because this location was closest to the 
