According to ANSI/ACCA Manual D, when balancing dampers are used, what is their preferred location in a duct system to reduce noise?

The preferred location for balancing dampers to reduce noise, according to ANSI/ACCA Manual D, is near the trunk duct takeoff. Placing dampers in this position helps to control airflow effectively and minimizes turbulence and noise that can occur when air is forced through the duct system. By installing balancing dampers closer to the trunk duct, airflow to various branches can be more accurately regulated, allowing for quieter operation as the air is distributed more evenly.

Situating dampers in this way maximizes performance and dynamic balancing of the system, while also preventing excessive noise that might arise from the higher velocity air moving through the ducts as it approaches the end points. Maintaining a proper airflow pattern and pressure also contributes to an overall quieter system, as it reduces the chances of whistling or other disturbances associated with high-velocity airflows near supply registers or at the ends of duct runs.

In contrast, putting dampers at the registers or further down the duct can lead to increased noise levels due to air turbulence and might hinder the efficient operation of the HVAC system.