When selecting an Air Handling Unit (AHU) for an HVAC system, there are several factors to consider. First, you must determine the size of the AHU based on the size of the space it will be servicing. The AHU should be sized to provide the necessary air flow rate and pressure drop for the space. Additionally, you should consider the type of filter and fan motor that will be used, as well as the type of coil and type of refrigerant. Finally, you should consider the noise level of the AHU, as well as any additional features such as variable speed drives or energy recovery systems. By taking all of these factors into account, you can ensure that you select the best AHU for your HVAC system.