04 — Tools
Calculate control cabinet cooling
A control cabinet gives off part of its heat through the enclosure surface – how much depends on the effective area, and that depends on how the cabinet is installed. Only what exceeds this has to be removed actively.
Result
- Required cooling capacityIn the design case
- —W
- Cooling capacity in the normal case
- —W
- Effective surface areaTo IEC 60890
- —m²
- Self-dissipation of the enclosure
- —W
- Cooling assessment
- —
- Dew point of the ambient airAt maximum temperature and assumed humidity
- —°C
- Heating power against condensationTo hold the internal temperature at the dew point at standstill
- —W
- Condensation assessment
- —
Please fill all fields with valid numbers.
A guide, not a design to standard. The applicable standards and case-by-case verification govern.
Worked example
The default case the calculator starts with, worked through once. Change the values above and it recalculates immediately.
Inputs
- Heat dissipation inside the enclosure
- 750 W
- Width
- 1.2 m
- Height
- 2 m
- Depth
- 0.6 m
- Installation
- Free-standing, all sides free
- Top surface
- Free
- Permissible internal temperature
- 35 °C
- Maximum ambient temperature
- 30 °C
- Expected ambient temperature
- 25 °C
- Minimum ambient temperature
- 5 °C
- Assumed relative humidity
- 60 %
Result
- Required cooling capacity
- 544 W
- Cooling capacity in the normal case
- 338 W
- Effective surface area
- 7.49 m²
- Self-dissipation of the enclosure
- 206 W
- Cooling assessment
- The requirement is in the range of a cooling unit. Filter ventilation is no longer sufficient once ambient temperature approaches the permissible internal temperature.
- Dew point of the ambient air
- 21.4 °C
- Heating power against condensation
- 675 W
- Condensation assessment
- Uncritical in operation, but not at standstill: if the enclosure cools to the minimum ambient temperature it drops below the dew point. An enclosure heater with a hygrostat prevents the condensation.
Formula
- Heat output: Q = k · A · ΔT with k = 5.5 W/(m²·K) for painted sheet steel
- ΔT = internal temperature − ambient temperature
- Cooling requirement = heat dissipation − heat output
- Free-standing: A = 1.8 · H · (W + D) + 1.4 · W · D
- Covered on top: the top area 1.4 · W · D drops out
- Dew point to Magnus: α = ln(φ/100) + 17.62 · t / (243.12 + t), τ = 243.12 · α / (17.62 − α)
- Heating power against condensation: P = k · A · (τ − minimum ambient temperature)
Assumptions and standards
- Effective surface to IEC 60890 depending on the installation type.
- k = 5.5 W/(m²·K) applies to painted sheet steel. Stainless steel is lower, aluminium higher.
- If the ambient is warmer than the permissible internal temperature, filter fans are ineffective – only a cooling unit will do.
- The covered top surface is simplified here: the top area drops out entirely. IEC 60890 lists separate rows with their own factors for covered surfaces. The simplification errs on the safe side – it reduces the area and therefore increases the calculated cooling requirement.
- The heating power is the value needed to hold the enclosure at the dew point at standstill – an upper bound. In operation a hygrostat switches, and the heat from the installed components contributes.
- Solar gain, installation in recesses and dirty filters worsen the result in operation.
Frequently asked
Where do I get the heat dissipation figure?
From the data sheets of the installed components. Drives, power supplies and transformers dominate; contactors and terminals barely matter. As a rough figure, drives dissipate about 3 % of rated power.
Is a filter fan enough?
Only if the ambient temperature is below the permissible internal temperature – a fan cannot cool below ambient. Otherwise a cooling unit or an air-to-water heat exchanger is needed.
Why does the installation matter so much?
A side placed against a wall or built into a row gives off hardly any heat. Between free-standing and enclosed on both sides there is easily a 40 % difference in effective area. The same applies to a covered top – a platform or cable floor resting on it takes the top area out of the calculation.
Why three ambient temperatures?
Because three different questions sit behind them. The cooling unit is selected for the maximum temperature, otherwise it falls short on the hottest day. The expected temperature says how much the unit actually runs. And the minimum temperature decides whether a heater is needed – the case most often overlooked.
What is the humidity for?
Temperature and relative humidity give the dew point. If the enclosure cools below that value at standstill, water condenses on the components. This is why corrosion appears in an unheated plant over winter even though cooling was adequate in summer.
Calculating is the easy part.
A formula gives you a number. Designing a plant also demands installation method, grouping, discrimination, the standards in force and a look at the installed base. That is what we take on.
Contact
Tell us what it is about.
A phone call or three lines is enough. From the very start you talk to the people who will later work on your project – not to a distribution list.
Direct
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- Emailinfo@fisekon.com
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33332 Gütersloh
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