What does the term 'draw-through' refer to in the context of AHU configuration?

In the context of Air Handling Unit (AHU) configuration, the term 'draw-through' refers to an arrangement where the fan is located downstream of the cooling coil and heating coil, effectively 'drawing' air through the coils. In a draw-through AHU, the fan pulls air through the filters, cooling coil, and heating coil before discharging it into the ductwork. This configuration creates a negative pressure on the upstream side of the fan and a positive pressure on the downstream side. A key advantage of the draw-through design is that it provides more uniform air distribution across the coils, as the fan pulls the air evenly through them. However, it also means that any leakage in the AHU casing upstream of the fan will draw unconditioned air into the airstream. In contrast, a 'blow-through' AHU has the fan located upstream of the coils, 'blowing' air across them. Draw-through configurations are commonly used in applications where precise temperature control and uniform airflow are critical. For example, in a hospital operating room, a draw-through AHU may be used to ensure that the air is evenly cooled and filtered before being supplied to the room.