What adjustments are made during air balancing to correct for over- or under-pressurization in specific zones of a building?

Air balancing is the process of adjusting an HVAC system to ensure that the correct amount of air is delivered to each zone or room in a building. Adjustments are primarily made using dampers, which are adjustable plates located inside ductwork. These dampers restrict or open airflow to regulate the amount of air reaching different zones. To correct for over-pressurization, where a zone receives too much air, the dampers in the supply ducts serving that zone are partially closed. This reduces the airflow to the zone, decreasing the static pressure and preventing excessive air delivery. Return air dampers in that zone may also be adjusted to ensure proper exhaust of air. To correct for under-pressurization, where a zone receives too little air, the dampers in the supply ducts serving that zone are opened further. This increases the airflow to the zone, raising the static pressure and delivering the required amount of air. Adjustments may also be made to the main supply fan speed, often controlled by a variable frequency drive (VFD), to increase overall system airflow. The balancing process involves measuring airflow at various points in the system, including supply registers, return grilles, and main duct branches. These measurements are taken using instruments like anemometers and pitot tubes. The measured airflow rates are then compared to the design airflow rates specified in the building plans. Based on these comparisons, the dampers are adjusted iteratively until the actual airflow rates closely match the design airflow rates in each zone, ensuring proper pressurization and temperature control throughout the building. The entire system needs to be considered as changing one damper affects the entire system.