The HVAC system of a vehicle plays a very important role in ensuring optimal thermal comfort for the passengers. In addition to maintaining the optimal temperature field in the cabin, the passenger must be able to choose the volume and direction of the flow as per their preference. Further, the pressure losses, particularly through the ducts and the vent of the system, must be minimized to ensure minimal energy consumption. This thesis aims to study these pressure losses, and quantify the effects of secondary turbulent structures that develop within them. To do so, new modelling workflows were proposed and developed with three different turbulence modelling approaches (RANS, URANS and DES).