The car manufacturer's ageing production plant was to be replaced with solutions that not only increase efficiency, but also contribute to sustainable climate management. A key aspect of this was the switch from the mounting plate to the 'Airstream' wiring system from Lütze. This was not only about mechanical advantages, but also about thermal advantages. The Eplan planning system was used to integrate the wiring system and the 'Airblower' fan in combination with a cooling unit into the system right from the start of the project. The aim was to create a needs-based cooling concept for the control cabinet combination under investigation. To this end, the temperature calculation tool 'Airtemp' carried out a series of simulations for future operating conditions. During series operation, the actual temperature situation was recorded and evaluated using measurements.

In accordance with the customer's wishes, the focus was on operational reliability; it should also be possible to make subsequent optimizations if anomalies were detected during the measurements. Lütze was supported by the University of Stuttgart, which has been conducting research into the thermal optimization of control cabinets for many years.

Planning and design of the system

The cabinets were designed in 3D and included all relevant components, whereby a theoretical analysis was carried out using the 'Airtemp' simulator. The input of various parameters such as installation location, ambient temperatures and power consumption of all components made it possible to calculate the thermal properties of the enclosures. As these were arranged openly, particular attention was paid to their behavior in relation to each other: The calculations showed that a simple summation of the enclosures was not sufficient, as air exchange and power distribution are not uniform.

Calculation of temperatures in the 3-zone model

Figure 1: Extract from Airtemp calculation of the individual cabinets. Supply cabinet without and with fan, drive cabinet without and with fan, and Airblower fan with air conditioner, control cabinet without and with fan (each from top to bottom).

© Sagittarius

Theoretical calculations were carried out for all enclosures using 'Airtemp' - in the first step with free cooling. The results(Fig. 1) show that with a simultaneity factor of 0.7 (i.e. all components are active 70% of the time and call up this power accordingly), a temperature of +40 °C was exceeded in at least one of the three zones in the enclosure. Although the results for two enclosures could be reduced to almost 40 °C by using the air blower, it was found that the enclosure with inverters still reached over +57 °C even with the air blower. An additional active cooling unit with a cooling capacity of around 550 W was therefore required to reduce the temperature to below the prescribed +40 °C. The selected cooling unit with a cooling capacity of 750 W is not operated at full load, which provides a sufficient buffer.

The calculations show that the fan has homogenized the temperatures. It remains to be seen what the actual distribution of temperatures under the cabinets will look like in reality. The calculations were deliberately carried out with tight limit values and a small buffer so that the results can be evaluated later.

The cooling concept

Taking into account analyses and experience from other measurements and projects, it was decided together with the customer to implement the row combination as follows: All Airstream frames were equipped with an air blower. The control cabinet containing the inverters was also to be equipped with a front cooling unit. The aim was to actively support the cabinet with the highest power loss with cold air when it was needed. The air blower should ensure that the air circulates around the frames and thus create a homogeneous climate. If the maximum acceptable internal temperature is exceeded, the cooling unit should be switched on to further reduce the average temperature level in the enclosure combination.

After one year of continuous operation of the system, the practical measurement project was launched. Two data loggers, each with nine temperature sensors and one humidity sensor, were integrated into the four control cabinet panels. At the same time, a measuring capsule was placed outside the control cabinet to record the ambient temperature and humidity. The measurements lasted a total of 18 months with regular monitoring. Targeted daily measurements were carried out on site for more in-depth analyses.

In the plant, which operates in three shifts, the measuring points were positioned in the open space (centrally in the front area, between the components and the enclosure door) at the bottom, in the middle and at the top in order to monitor the three zones. In addition, sensors were placed between and above the components that generate a lot of heat. In this way, all cabinets could be monitored.