KEVOS® MAKEOS · Engineering
Enclosure Cooling Airflow (Heat Load, Wall Losses, Fan Airflow Needed)
For an electrical or control enclosure with equipment giving off heat, how much heat escapes through the walls, and what fan airflow keeps the inside within its temperature limit?
Ventilation of a closed cabinet: the heat lost through the enclosure surface at the temperature difference from a wall heat transfer coefficient, the heat the fan must remove, the mass and volume of air per hour to carry it at the allowed temperature rise (as the heating energy tool, applied to the cooling air), and the fan airflow against the fan you have.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Heat given off inside | W | Total heat given off by drives, power supplies and other equipment inside. |
| Highest outside air temperature | °C | Highest temperature of the air drawn in. |
| Highest allowed inside temperature | °C | Highest temperature the equipment inside may see. |
| Effective enclosure surface area | m² | Surface area of the enclosure that can lose heat (walls against other walls or the floor count less). |
| Wall heat transfer coefficient | W/(m²·K) | Heat transfer coefficient through the walls to still air (about 5.5 for painted steel). |
| Air density | kg/m³ | Density of the air at the inlet. |
| Air specific heat | kJ/(kg·K) | Specific heat of air. |
| Fan airflow (at its working pressure) | m³/h | Airflow of the fan at the pressure drop of its filters and grilles. |
Method and formulas
- Wall loss = k A (T_inside − T_outside); fan heat = heat load − wall loss.
- Air mass per hour to carry the fan heat with a rise of T_inside − T_outside: m = Q ÷ (c_p ΔT) (as the heating energy tool, Q = m c ΔT).
- Airflow = mass ÷ density.
- Example: the walls lose 110 W; the fan must move 120.43 m³/h.
Limitations
- Air drawn in at the outside temperature and leaving at the inside limit; poor air paths leave hot spots.
- Solar gain on outdoor cabinets is not included.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a filter fan for a control cabinet
- Check whether a panel needs a fan at all
- See the effect of a hotter plant room
Who it is for
- Electrical engineers
- Panel builders
- Maintenance engineers
What you get
- Heat lost through the walls
- Heat for the fan to remove
- Airflow needed against the fan
Interpreting the result
- When the inside limit is close to the outside temperature, the airflow needed rises steeply; an air conditioner may then be the better answer.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 371–374, 2683. Topic reference; no source tables or recommended settings are reproduced.
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Open the Enclosure Cooling Airflow (Heat Load, Wall Losses, Fan Airflow Needed) calculator
