The Panel That Overheated in Summer: Electrical Enclosure Cooling
A control panel in a non-air-conditioned plant. In winter, the panel ran at 35°C. In summer, it reached 55°C. The PLC started faulting at 50°C. The panel had no cooling — just a vent on the door. The drive’s heat was baking the PLC. This is how to size panel cooling.
The heat load
Every component in the panel generates heat. The VFD (variable frequency drive) loses about 3-5% of its power as heat. A 5 kW VFD generates 150-250 W. The PLC, servo drives, power supply, and relays add another 50-100 W. Total heat load for a typical machine panel: 200-400 W.
Q_heat = P_load × (1 – η)
Where P_load is the power consumed and η is the efficiency. For a 5 kW VFD at 97% efficiency: Q = 5000 × 0.03 = 150 W. Add the PLC and other components: 250 W total. The panel needs to dissipate 250 W to stay at 35°C when the ambient is 35°C. In summer, the ambient is 40°C. The panel will run at 45-50°C without cooling.
The cooling options
| Method | Cooling capacity | Cost | Best for |
|---|---|---|---|
| Vent (natural convection) | 50-100 W | Low | Low heat loads, cool plants |
| Filter fan (exhaust) | 200-500 W | $100-200 | Dust-free environments |
| Air-to-air heat exchanger | 200-800 W | $300-600 | Dusty/oily environments |
| Air conditioner (closed loop) | 500-2000 W | $800-2000 | High heat, washdown, outdoor |
| Peltier (thermoelectric) | 50-200 W | $200-400 | Small panels, low heat |
What we did
We installed a filter fan on the panel door. The fan draws cool plant air through a filter, circulates it through the panel, and exhausts the hot air out the side. The fan moves about 30 m³/h, which dissipates the 250 W heat load. The panel temperature dropped from 55°C to 38°C. The PLC stopped faulting.
The filter fan requires a filtered air intake (to keep dust out) and an exhaust vent on the opposite side. The filter needs replacement every 6 months (we added it to PM).
The closed-loop option
For a dusty or oily environment, a filter fan draws in contaminated air. Use an air-to-air heat exchanger instead: the inside air circulates through the exchanger, and outside air cools the fins without mixing. The panel stays sealed. The heat exchanger costs more but requires less maintenance (no filter replacement).
The temperature rating
Most PLCs are rated for 0-55°C. Servo drives are rated for 0-40°C. If the panel exceeds these, the components fault or shorten. The target panel temperature is 35°C maximum (20°C margin below the 55°C limit). In a 40°C plant, the panel needs active cooling to stay at 35°C.
The cooling rule: Calculate the heat load (VFD losses + electronics). Size a fan or heat exchanger to dissipate it. Target 35°C panel temperature. In a hot plant (40°C ambient), don’t rely on vents — they won’t be enough. A filter fan costs $150 and prevents PLC faults that cost thousands in downtime.
