Enclosure Thermal Sizing Calculator
Estimate passive heat dissipation and required active cooling capacity for an industrial enclosure.
Note: This tool gives a practical engineering estimate for steady-state conditions. Final product selection should follow manufacturer data and site-specific constraints.
What is a Rittal therm calculator?
A Rittal therm calculator helps estimate whether your electrical enclosure can stay within safe operating temperature limits using passive heat dissipation alone, or if you need active cooling such as a filter fan, heat exchanger, or air conditioner. In control cabinets, overheating can shorten equipment life, cause nuisance trips, and reduce reliability.
How this calculator works
The calculator combines enclosure geometry, heat load, ambient temperature, and mounting/material assumptions to estimate cooling performance:
- k = overall heat transfer coefficient (depends on enclosure material/surface behavior)
- A_effective = usable enclosure surface area after mounting correction
- ΔT = allowed temperature rise (max internal temperature − ambient)
If total heat load exceeds passive dissipation, the calculator returns required active cooling capacity in W and BTU/h.
Key assumptions
- Steady-state thermal conditions (not short transient spikes)
- Uniform enclosure temperature distribution
- Reasonable airflow around exposed enclosure surfaces
- No major internal hot-spot modeling
Input guidance
1) Enclosure dimensions
Use external dimensions in millimeters. The model computes total geometric surface area and then applies a mounting correction to represent blocked surfaces or reduced convection.
2) Heat load (W)
Sum the thermal losses of drives, power supplies, PLCs, contactors, and other components. If exact losses are unknown, use manufacturer dissipation data or conservative estimates.
3) Ambient and maximum internal temperature
Set ambient to realistic worst-case local conditions. Then set the highest acceptable internal temperature based on your most temperature-sensitive component.
4) Material and mounting
Material affects heat transfer. Mounting greatly changes effective area. A tightly packed row of enclosures usually rejects less heat than a free-standing cabinet.
Interpreting results
- Passive capacity ≥ heat load: passive cooling may be enough.
- Passive capacity < heat load: active cooling is needed; select a unit at or above the calculated capacity (with margin).
- Predicted internal temperature without active cooling: useful for quick risk checks.
Practical engineering tips
- Always validate using worst-case summer ambient values.
- Consider dust, oil mist, and humidity when choosing fans vs closed-loop cooling.
- Keep cable ducts and high-loss devices arranged for internal airflow.
- Add design margin for aging filters, fouling, and future load growth.
- If electronics are critical, consider redundancy or alarm thresholds.
FAQ
Is this an official manufacturer sizing engine?
No. This is a practical estimator designed for quick thermal planning and preliminary sizing.
Can I use this for outdoor cabinets?
Yes, but you should include realistic solar/external heat gain and verify final performance with detailed environmental assumptions.
Why include a safety margin?
Real installations vary from ideal assumptions. A safety margin helps avoid undersizing and improves long-term reliability.