Control Panels
Control Panel Heat Load and Temperature Rise
Internal temperature rise for a control enclosure from component heat, solar gain, and enclosure surface area, with the cooling shortfall if any.
Results
- Predicted internal temperature
- 58.3C
- Temperature rise
- 23.3C
- Effective surface area
- 1.951m2
- Passive dissipation available
- 161W
- Cooling required
- 89W
- Predicted internal temperature
- 136.9F
35 C ambient plus 23.3 C rise
21.0 sq ft
At a 15.0 C allowable rise
The enclosure cannot shed this passively. A filtered fan, a vortex cooler, or an air conditioner is needed.
The arithmetic
- Effective area = 1.951 m2 (21.0 sq ft), back surface excluded
- Total heat = 250 W components + 0 W solar = 250 W
- Rise = 250 W / (1.951 m2 x 5.5 W/m2/C) = 23.3 C
- Internal = 35 C + 23.3 C = 58.3 C
What this does not account for
- The heat transfer coefficient depends on the enclosure material, finish, and airflow. Stainless steel and unpainted surfaces perform differently from painted steel, and the manufacturer figure should be used where available.
- Solar gain on an outdoor enclosure is often the dominant term. A sunshield changes the answer substantially.
- This is a steady-state estimate for natural convection. It does not model internal hot spots, and a drive can be far above the average internal temperature at its own heatsink.
- Power supplies and drives derate above their reference ambient. Check the derating curve at the predicted internal temperature, not at the outdoor ambient.
- The predicted internal temperature exceeds what you entered as allowable. Add cooling, increase the enclosure size, or reduce the heat load.
How this is calculated
Enclosure temperature rise is the total internal heat load divided by the product of the effective surface area and the heat transfer coefficient. For a painted steel enclosure in still air, a coefficient of roughly 5.5 watts per square metre per degree C is commonly used. Solar gain on an outdoor enclosure is frequently the largest single term and is regularly left out.
Formulas
dT = Q / (A x k)
- dT — temperature rise above ambient, degrees C
- Q — total internal heat load in watts, including solar gain
- A — effective surface area in square metres
- k — heat transfer coefficient, about 5.5 W/m2/C for painted steel in still air
Assumptions built into this calculator
- Natural convection with no forced air, no vents, and no active cooling.
- Wall mounting treats the back surface as ineffective, which is the conservative assumption.
- Steady state. Does not model warm-up, internal hot spots, or stratification.
- The default coefficient is a commonly used figure for painted steel and is not specific to any product.
Frequently asked questions
- Where do I get the heat load figure?
- From the datasheet of every component that dissipates power. Drives, power supplies, and transformers dominate. For a power supply, the dissipation is the delivered load multiplied by (1 divided by efficiency, minus 1).
- How much solar gain should I assume?
- It depends on orientation, latitude, colour, and whether there is a sunshield. Enclosure manufacturers publish figures for their products, and those should be used rather than a generic number.
Direct contact
Have a controls question?
Reach Eric Sullivan directly about anything on this site, a controls or automation topic, or one of his personal projects.