The Panel That Overheated in Summer
We mounted a control panel (PLC, servo drive, power supply) in a sealed enclosure. On the bench (20°C), it ran fine. In summer (35°C plant), the panel overheated (the drive faulted “overtemp”). The problem: the panel was sealed (no ventilation). The drive (which dissipates heat) heated the panel. The internal temperature rose to 50°C. The drive faulted. We added a filtered fan (an intake fan) and an exhaust vent. The panel ventilated (air flows in, out). The internal temperature dropped to 35°C. The mistake was sealing the panel without ventilation (the heat has to go somewhere).
Panel enclosure ventilation cools the electronics. This article covers the design.
The Heat Load
The panel’s electronics (PLC, servo drive, power supply) dissipate heat. A servo drive dissipates 3–5% of its power (a 1 kW drive dissipates 30–50 W). A power supply dissipates 5–10%. Sum the heat load (Watts). The enclosure must dissipate the heat (via ventilation, or a heat exchanger).
Step 1: Natural Ventilation (Slots)
For a light load (under 100 W), natural ventilation (slots in the enclosure) is enough. The hot air rises (convection), exits through the top slots. Cool air enters through the bottom slots. No fan (passive). But it’s not filtered (dust enters). For a clean environment, natural slots are fine.
The ventilation rule: The panel that overheated was sealed (no ventilation). For a heat load of 100–500 W, add a filtered fan (intake) and an exhaust vent. For over 500 W, use a heat exchanger (or air conditioner). The heat has to leave.
Step 2: Fan and Filter (Forced Ventilation)
For a medium load (100–500 W), add a fan. The fan (mounted at the bottom) draws cool air in (through a filter). The hot air exits through a vent (at the top). The fan pushes the air through the panel (over the drives). The filter keeps the dust out (article 147). Size the fan for the heat load (the fan’s CFM, or m³/h).
Step 3: Heat Exchanger (For Dirty Environments)
For a dirty or corrosive environment (washdown, dust), don’t draw plant air (it’s dirty). Use a heat exchanger (a closed loop, the panel air is separate from the plant air). The heat exchanger transfers the heat (without mixing the air). More expensive, but keeps the panel clean.
Step 4: Air Conditioner (For High Load)
For a high load (over 500 W) or a high ambient (40°C+), use an air conditioner (a panel AC unit). The AC cools the panel (below ambient). Expensive, but needed for a heavy load (or a hot plant).
| Heat Load | Cooling |
|---|---|
| <100 W | Natural slots (passive) |
| 100–500 W | Filtered fan + exhaust vent |
| 500–1000 W (dirty) | Heat exchanger (closed loop) |
| >1000 W (or hot plant) | Panel air conditioner |
Step 5: Thermostat
Control the fan with a thermostat (a bimetal switch). The fan turns on when the panel is over 35°C (and off when it’s cool). The fan doesn’t run 24/7 (it lasts longer). For a heat exchanger or AC, the thermostat controls it.
A Panel Ventilation Checklist
- What is the heat load? (Sum the drives/supplies?)
- What is the plant ambient? (°C?)
- Is the panel sealed? (Needs ventilation?)
- For 100–500 W: filtered fan?
- Is the filter cleanable? (Article 147?)
- For dirty: heat exchanger? (Closed loop?)
- For high load: AC? (Panel unit?)
- Is there a thermostat? (Controls the fan?)
- Does the panel overheat? (Summer? Test?)
- Is the IP rating maintained? (Article 77?)
The Bottom Line
Panel enclosure ventilation removes the heat. The panel that overheated was sealed. Add a filtered fan (for 100–500 W), a heat exchanger (dirty), or an AC (high load). Control with a thermostat. The panel that didn’t overheat wasn’t the biggest enclosure — it had ventilation.
