RSES Journal Winter 2025, RETA-RSES

Optimizing AHU Performance with Winter Maintenance

Air handling units play a vital role in commercial building performance—from supporting energy efficiency to enhancing indoor air quality and maximizing occupant comfort. That is why it is critical to keep them running properly.

BY MARK MILLER & JEREMY FITZE

A s the airside portion of many commercial heating, ventilation and air conditioning systems, air handling units (AHU) condition and circulate ventilated air through the build ing’s duct system. The equipment pulls in return air from the conditioned building through the return duct system or plenum. Depending on the design, return fans can help to recirculate a portion of the return air back to the AHU, while the exhaust system removes the remainder from the building. A portion of that exhaust air may then be exhausted from the building through exhaust dampers or fans to help maintain proper building pressure and indoor air quality (IAQ). The AHU introduces outside air through a series of modulating dampers, mixing it with the return air in a mixing plenum, and then passing it through a filtration system. Filtered air is then heated and/or cooled, often by a chiller, boiler, or variable refrig erant flow (VRF) system, where humidity levels may also be adjusted, and then finally distributed through the building via supply fans. Economizers may also be integrated to enable energy-efficient free-cooling when ambient conditions are suitable. Proper equipment maintenance is key to ensuring optimal AHU performance, espe cially when the equipment is located on the

Photo courtesy Johnson Controls/YORK.

roof where it can be exposed to extreme weather conditions, outdoor contami nants and debris. A proactive maintenance approach can help ensure proper airflow is maintained while mitigating premature system wear and unplanned downtime. Although maintenance protocols can

vary based on geographic location, appli cation requirements and manufacturer’s guidelines, the winter season is an ideal time to prioritize AHU service. Making the Case for Maintenance Winter can be especially taxing on roof

10 RSES Journal WINTER 2025

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