Commissioning Case Study: Diagnosing Airflow Loss in Dual-Wheel Energy Recovery Units

As part of a larger project, MSC assisted with the commissioning and turnover of two large 60,000 CFM air handlers that were experiencing unexplained performance issues. Each unit served two floors of specialized research laboratories and incorporated two 16-foot-diameter energy recovery wheels as part of its energy recovery unit (ERU) function. Unlike a conventional system with a single wheel handling both sensible and latent energy, each of these units used two wheels within the overall air-handling system, with one dedicated to sensible energy (temperature) recovery and the other to latent energy (moisture) recovery. This unusual configuration was a key factor in understanding the performance issues.

Each 16-foot wheel rotated at a slow, single-digit RPM, driven by a small, high-torque motor on a variable frequency drive (VFD). Roughly 30 days after the system had been air balanced, supply and exhaust airflow in the laboratories began dropping by more than 10%. Temperature and humidity recovery efficiency declined right along with it.

Large supply fans pushed air through the lower portion of each ERU, while a separate set of high-plume exhaust fans pulled air through the top portion of the wheels. The question was clear: why was airflow dropping so quickly, and why was recovery efficiency following the same trend?

Finding the Root Cause

The supply and exhaust fan drives had crept up to 59-60 Hz, well above their original setpoints. But the real answer came from diagnosing the ERUs while they were running, not while they sat static. Once the wheels were brought up to speed, the problem was visible almost immediately: the pie-shaped wheel sections were uneven, with some protruding as much as an inch out of plane.

This misalignment, caused by faulty installation, accelerated mechanical wear between the wheels and their gasketing systems, prematurely degrading the seals and creating significant bypass between supply and exhaust airstreams. The longer the units ran, the worse it got.

The Fix

Correcting the issue required a substantial hands-on effort. The team ordered new gaskets and seals for all four wheels, plus one spare set. Working one ERU at a time, technicians readjusted every section on each wheel and retested at high RPM to confirm true, even rotation, a process that took several days per wheel given their size.

Once each wheel ran true under maximum RPM, the team replaced all gaskets and brushes, then retested seal performance against the manufacturer's tolerances to minimize bypass. New belts were also installed and aligned on the wheel rotation motors.

Results

The VFDs dropped back down to their intended operating speed almost immediately. Follow-up airflow readings across the labs and air handlers confirmed correct supply and exhaust volumes, including at the fume hoods throughout the facility.

The commissioning team and construction manager were pleased to see the labs back at design intent, with proper airflow, heat exchange, and humidity control restored across all wheels. The ERU manufacturer's technical representative confirmed the results using calibrated instruments.

Are your building systems facing unexplained airflow or efficiency issues? MSC's commissioning team has the diagnostic expertise to find the root cause and get your equipment back to design intent. Contact us today to schedule an assessment.