UNIT SECTIONS Exhaust Supply IDENTIFYING THE CULPRIT With our fi ndings recorded, we began to meet with the engineer and manufacturer to see where we could locate the discrepancy. The three energy recovery units had been pressure leak tested by the manufacturer. Could the casings of the units now be the issue? The exhaust airflow was within design. Could it be internal leakage? The manufacturer stated this was not possible. Even though we were told that the issue was not in the unit, we began to formulate the factors which may be leading to our missing air. It was not possible to directly measure airflow after the TAB Journal Summer 2019 exhaust fans. Plotting the exhaust test results on the fan curve, we found that we had 20 percent higher air volume and using 25 percent more brake horsepower than we should be if we were at the design conditions and from incoming traverses. Fan curves are not always the most accurate means of determining performance from field tests, but having this information helped point us in the right direction. The next step was to isolate and test each side of the unit individually. We tested the outside air supply fi rst; we turned off the exhaust fan side and sealed all exhaust openings, 11