A VFD trips on over temperature every summer afternoon. Someone adds a fan at the cabinet bottom blowing in. The drive still trips, and now the filters are caked with dust. The airflow path was never set up to move the hot air out.
Hot air rises; work with that
Electronics heat the air around them. Hot air is less dense and rises to the top of the cabinet. If the exhaust fan sits at the top, it pulls the hottest air out and draws cooler air in through filtered inlets near the bottom. That creates a natural flow path across the components.
Put a blower at the bottom forcing air in without a matching exhaust and you pressurize the cabinet unevenly. Air finds the easiest way out, often through cable glands, while hot pockets sit at the top where the fan isn’t.
Filtered inlet, unobstructed exhaust
The intake side needs filters to keep dust out. The exhaust fan can be less filtered because air is leaving, not entering. Check the inlet filters regularly; a clogged filter starves the fan and the cabinet cooks despite the fan running.
Match inlet and exhaust airflow. If the exhaust pulls more air than the inlets supply, it draws dust through every cable opening. Balance the flow so the cabinet runs at slight positive or neutral pressure.
When fans aren’t enough
In a dirty or corrosive environment, fans pull contaminants in no matter how good the filters are. A sealed cabinet with an air-to-air heat exchanger keeps the enclosure closed. In hot ambients, compressor-based cabinet air conditioners drop the internal temperature below the room temperature, which fans can never do.
Don’t size cooling by the fan catalog alone. Add up the heat dissipation of the VFDs, power supplies, and transformers, and size for the worst-case summer ambient. That’s the number that matters.
Internal air circulation
A big cabinet with dense ducting can have hot spots even with correct exhaust. Internal fans or baffles move air across the heat sinks and prevent pockets. Leave clearance around VFDs; crowding them against wiring ducts blocks their own cooling fans.
