Through the increasing automation of production processes more and more electro- technical components are being used. These components generate a lot of power loss which convertsinto heat. The increasing temperatures inside the enclosures have a negative influence on the life cycle of the components inside.
Supporting process reliability and keeping service intervals within economic reasons are the main challenges thermal management of industrial enclosuresis facing today.Therefore the choice of the right cooling method is very important.
The most common cooling methods used:
1. Natural convection
If your application has only a small heat loss, openings in your enclosurewith louversor grills with filters can be effective enough. However in most cases this method does not provide enough cooling for today‘s electronic components.
Ruleof thumb:
- depending on the heat load inside the enclosure and the temperature outside, the enclosuretemperature is likely to be higher than the ambient temperature.
- no moving parts - by eliminating external fans, you create a zero maintenance application
- no dirt - utilising exhaust filters prevents dirt from entering into the enclosure. Dirt can damage electronics as much as heat does!
If the ambient temperature is lower than theenclosure temperature,the heat will bedissipatedthrough the enclosure surface.
The following simple formula calculates the level of heat dissipated from the enclosure:
Ps [W]= k xA x∆T
Ps [W] =Dissipated power (thermal power dissipated from the surface area of the enclosure)
k [W/m²K] = Coefficient of heat transmission (Dissipated power per m²surface area and1 K difference in temperature). This constant is determined by the material.¹⁾
A [m²] =Surface area of the enclosure
∆T [K] = Temperature difference between ambient air and internal enclosure air
¹⁾Sheet metal: 5,5 W/m²K / Stainless steel:5,5 W/m²K / Aluminium: 12W/m²K / Plastic: 3,5 W/m²K
2. Forced convection
If your installation is in a clean, non-hazardous environment with an ambient temperature less than the desired enclosure temperature, a simple forced ventilation system utilizingthe ambient air is usually sufficient. Filter fans combined with exhaustfilters can generally meet the heat dissipation needs of modern electronic components.
Ruleof thumb:
- calulated rise should be at least +10 Kelvin above ambient temperature(can vary depending on the load inside the enclosureand the ambient temperature).
- multiple configurations possible – filter fans can be located in a number of locations within complex enclosure configurations.
- calculate the size of a fan including thestatic pressure – understanding how static pressure affects the performance of a fan is very important when choosing filter fans.
The following simple formula calculates the required airflow:
V = 3.1 xPv /∆T[ m³/h]
V [ m³/h] = Air flow volume of a filter fan
Pv[W] = Power loss (thermal power generated inside an enclosureby the dissipationloss of components)
∆T [K] = Temperature difference between ambient air and internal enclosure air
3. Cooling through a closed cooling circuit:
If your application is installed in an environment with high ambient temperatures, oil and dust exposure and you have high splash proof requirements (NEMA / IP), then it becomes absolutely necessary to prevent the ambient air from entering the enclosure.
A cooling system with closed loop cooling normally consists of 2 circuits; one circuitcloses the ambient air off and cools and circulates clean air into the enclosure. The second circuit uses the ambient air or water to dissipate the heat.For these kind of applications cooling units and air/water heat exchangers are normallyused.
Ruleof thumb:
- the only method to reduce enclosuretemperature below ambient temperature(using cooling units and air / water heat exchangers)
- suitable for high NEMA / IP requirements
- during planning you need to take the ambient temperature and the generated power loss into consideration. For outdoor applications, please also consider the solar load.(check the performance charts of the product you want to use to ensure that your system temperature is properly maintained)
The right selection of a cooling unit is determined by the following criteria:
- required cooling capacity in Watt
- max. ambient air temperature and desired enclosure air temperature
- mounting requirements (wall, recessed or top mount)
- dimensions of cooling unit and enclosure
- mounting environment (indoor, outdoor, shading, etc.)
The following simple formula calculates the necessary cooling power:
Pk = Pv - Pr
Pk[W] = Cooling capacity of the unit
Pv[W] = Power loss (thermal power generated inside an enclosureby the dissipation lossof components)
Pr[W] =Radiant heat gain/loss (heat transfer through the outer bodyof the enclosure)
The following formula calculates the heat gain/loss:
Pr = k xA x∆T
k [W/m²K]= Coefficient of heat transmission
A [m²] = Enclosuresurface area
∆T [K] = Temperature difference between ambient air and internal enclosure air
Furthermore, the following should be noted:
- the enclosure should be sealed to prevent the inflow of ambient air
- the NEMA / IP rating of the cooling unit and of the enclosureshould be the same
- use a door contact switch to prevent operation with open doors
- ensure that the external circuit has a goodair inflow and air outflow, so that theheat can be dissipated into the environment
- it also must be ensured that components with a high level of self-ventilation do not direct the air into the cold air outlet of the cooling device.
- ensure the enclosure is standing straight.
- setting the temperature to the lowest is not always the best solution. The pre-set value of+35°C is a good compromise ensuring long life of electrical components, efficient operation and minimum condensation. This canvary depending on the application.
