Tests at an Audi factory have shown that an alternative form of cabinet wiring can cut internal temperatures, extending the life of critical components inside the cabinets. As Lütze’s cabinets product manager, Michael Bautz, reports, the reduction was greatest at hotspots that are critical for many components.
While the components used in control cabinets are generally becoming smaller, their heat dissipation is increasing and cabinets are getting hotter. More efficient cooling systems obviously help, but the way the cabinets are wired can also have an effect.
One approach to cutting heat levels is to separate the heat-emitting components from the cabling using a wiring frame rather than using conventional mounting plates and trunking. This directs cold air downwards to the rear of the cabinet and then to the front and up again, creating a cool zone to the rear, where most of the cabling is located. A permanent circulation of air is generated between the warmer wiring at the front and the cooler wiring at the back.
Traditional v’s Alternative Cabinet Cabling Technologies
An Audi engine factory in Hungary was recently used as a testbed to compare the traditional and alternative cabinet cabling technologies. The plant, in Györ, includes automated production lines that press valve seat rings and valve guides into the cylinder heads of V6 Otto engines. The test involved two of the site’s production systems, each using four control cabinets with the same construction.
The cabinets are 2000mm high and 600mm deep. Three cabinets in each system were 1200mm wide, while the fourth was 600mm. For the test, one of the four cabinets in each system was monitored. The first cabinet was equipped with a conventional mounting plate and was cooled using an air-conditioning system with a 1.5kW heat loss. In the second cabinet, the mounted components were separated from the wiring using a wiring frame – Lütze’s AirStream system.
The AirStream cabinets don’t use trunking that might impair airflows and were cooled using 1.45kW heat exchangers. The relative power losses of the two cooling systems was a minor factor because the cold air came from the roof. Instead, the study focused on verifying the effect of guided air inside the control cabinet.
In the alternative system, the air circulates freely, unlike in cabinets with conventional mounting plates. Measurements were carried out over two days and taken for six hours at a time with ten sensors recording ambient and internal temperatures. The power consumption of the two systems was not examined because it was assumed that the clocking was identical.
Measuring Temperatures at Critical Points
Temperatures were measured at critical points in the cabinets – e.g. components with high heat losses. After the air-conditioning system was started in the cabinet using the mounting plate (about 40 minutes after the production start-up), the temperatures fluctuated between 29°C and 43°C. The temperature measured between a contactor and the trunking was 38.5°C – 42.5°C, indicating an air blockage, while the temperature between a Siemens Simatic ET200S I/O system and a cable duct was 36.5°C – 38.5°C. At the air intake of the air-conditioning system, the temperature was 33.5°C.
The trunking hotspot remained just within the tolerances because the system is designed for an external temperature of 38°C and a maximum internal temperature of 42°C. In the cabinet with the new wiring frame, temperatures were measured after the heat exchanger had started to operate (a maximum of 37 minutes after the production start-up). The temperatures fluctuated between 30°C and 34°C. The temperature between a contactor and the ET200S in this cabinet was measured as 31°C – 33.5°C, while between the ET200S and the terminals it was 32°C – 33.5°C. At the air intake of the heat exchanger, the temperature was 29.5°C.
If the temperature of the air at the outlet of the heat exchanger was identical to the temperature of the air-conditioner, the curves would rise linearly. Despite this, the air is not layered as happens when a mounting plate is used. Hotspots in the new wiring frame system were barely detectable. When the cabinet incorporating the wiring frame was tested, the ambient temperature was 23.9°C – some 1.9°C higher than when the cabinet with the mounting plate was tested. If the external temperature had been the same, the cabinet with the wiring frame would have been 1.9K cooler and the curves would have been even lower.
The tests demonstrated that using a wiring frame can achieve noticeable cooling and a consistent climate inside control cabinets, protecting installed components from the heat & increasing their life expectancy. Further improvements could be achieved by routing cool air to minimise hotspots around components with particularly high heat losses. Further analysis using Lütze’s online AirTemp application also reveals that air-conditioning wouldn’t be needed using the wiring frame. Assuming an ambient temperature of 25°C and that 70% of the components would be operating at the same time, fan-based cooling would be sufficient.
Looking for More Information? LC Automation Can Help With That…
For more information download the Lutze AirStream Wiring System Catalogue or Lutze Airstream Compact – For Compact Control Panels.
Lutze also have an excellent white-paper which looks at the background information and theories you need to consider when thinking about the temperatures in your control panels. You can download Thermodynamic Considerations for Control Panels here.
If you have a specific question or would like to discuss cooling in your control panels, please call LC Automation on 01254 685900. Our Technical Support Engineers will be able to help you select the best solution for your application.