MSC Provides Diagnostics on Commissioning and Air Balancing of New Laboratory

MSC was called in to take a look at static pressure and airflow problems occurring during commissioning and air balancing of a new laboratory HVAC system consisting of two air handlers with standby backup. Air balancers were running into difficulty with static pressure and balancing to the design CFM.

MSC’s diagnostic team took calibrated hood readings for all diffusers and registers on supply and exhaust. Several lower-than-expected exhaust readings prompted a review of the related ductwork and several traverses. It was determined that a large pressure drop was taking place in two branches of the exhaust duct due to configuration issues in certain areas. A simplified duct transition was installed to remove the excessive static pressure drop, thus returning proper flow.

Continuing with the investigation, CFM and static pressure were still a little low for the backward incline fan, and VFD drive speed was high, which didn’t leave much room to overcome filter loading with some spare capacity. Further review found excessive leakage at isolation dampers situated between the new and standby systems that were not closing and sealing properly. During simple point-to-point testing of the actuator and linkage through the BAS system, and when operated mechanically by hand, the dampers operated correctly. It was determined that the actuator torque was undersized and unable to overcome system airflow and static pressure dynamics. The successful solution was to install adequately sized actuators.

After identification and repair of the anomalies, MSC assisted in performing traverses and calibrating the system airflow stations. Static pressure was checked throughout the system and several minor repairs were made to Setra differential pressure transmitters down in the space. VFD hertz and fan speed were now under control at about 75% capacity, sufficiently overcoming filter loading with spare capacity beyond. Air balancing and static pressure cascade were quickly achieved shortly thereafter to complete the commissioning process on time.