Enclosures for electrical components have countless fields of application in industry. There are many designs that are standardized in terms of the components used and application purposes, but there is also a great deal of individuality. In addition, even enclosures that appear to contain identical components at first glance can have different temperature distributions. In a specific application, for example, the cycle time of the process to be controlled determines what thermal power loss is released in an enclosure. Factors such as component placement also strongly influence the individual temperature to which a single component is exposed.

There is no universal cooling mechanism that enables worry-free operation for all applications and eventualities and is also energy-efficient. It is therefore crucial to think about the climate in the enclosure as early as the planning phase. Mistakes that are made affect the entire life cycle of the system and can only be rectified at a later date with additional time and financial resources.

Friedrich Lütze and the Institute for Building Energy, Thermotechnology and Energy Storage (IGTE) at the University of Stuttgart are working on needs-based and environmentally friendly cooling concepts for control cabinets as part of a long-standing collaboration. This is because the demand for greater energy efficiency in industry has also reached the enclosure sector. And other requirements are also becoming increasingly important for system operators - such as protection against thermally induced failure. After all, as a result of the digital transformation and the associated strong networking of all production steps, even the smallest failures in control cabinet functionality can have far-reaching consequences. Last but not least, public and political pressure to reduce emissions at every stage of production is increasing. A holistically calculated CO2 footprint of an industrial product also includes the emissions caused during production.

In the following, a frequently occurring but little-noticed case study is used to show how a seasonal and needs-based cooling concept can be used to reduce energy consumption and emissions.

A look at thermodynamics

Most climate considerations in the enclosure sector focus on individual enclosures. However, in practice, combinations of enclosures without separating internal walls are just as common as individual enclosures. From a thermodynamic point of view, the installation situation and the spatial separation of an enclosure have a very strong influence on its climate. In standard enclosure combinations, active cooling - an air conditioning unit or heat exchanger - is often only fitted to every second or third enclosure. If only the characteristic data such as power loss per enclosure and maximum usable cooling capacity are considered here, operation seems possible. In reality, however, the picture is different. The following practical example shows the energy saving potential that often remains unused.

Figure 1: Temperature field for non-optimized state (left) and optimized state (right). Free cooling and cooling with 'Airblower' on the left.

© IGTE

If several enclosures share an active cooling system (air conditioning unit or heat exchanger), a distribution problem often arises. This can be clearly illustrated using a CFD simulation. Figure 1 shows the temperature distribution in an enclosure combination without separating inner walls, consisting of two enclosures. Both enclosures are constructed with the 'Airstream' ductless wiring system from Lütze. The right-hand cabinet has active cooling, the left-hand cabinet does not. The left-hand section of Fig. 1 shows the initial situation: the left-hand cabinet is operated with free cooling, which means that there is only very low air circulation due to thermal buoyancy. The CFD simulation shows that no cold air arrives in the left-hand cabinet and that numerous hotspots form in the upper area. The actively cooled cabinet on the right is thermally harmless, as it provides sufficient cooling capacity. However, if the left-hand cabinet is also to be cooled sufficiently with this configuration, the cooling capacity introduced must be significantly increased. This also causes the temperature of the air in the actively cooled cabinet to drop sharply - the large temperature differences pose a risk of condensation forming.

A more effective solution is to distribute the cold air better between the cabinets. The right-hand section of Fig. 1 shows how this can be achieved: In this optimized state, there is an 'air blower' in each of the cabinets - a circulating air blower of the 'Airstream' wiring system - which can generate a directed circulation flow around the wiring frame. This is sufficient to introduce a comparatively low cooling capacity into the right-hand cabinet. By breaking up the temperature stratification and the much higher air circulation rates, the climate in both enclosures is improved and the hotspots in the previously heavily loaded left-hand enclosure are eliminated. An 'Airblower' in controlled operation has an electrical power consumption of just 15 W. The special feature is that the control unit of the 'Airblower' can control the individually used device for active cooling (e.g. air conditioning unit or heat exchanger) via an additional potential-free output. Temperatures in the cabinet can be recorded via several Pt100s and used as control variables.

Development over one year of production

The energy benefits of this cooling concept can be illustrated by considering an entire production year.

The temperature in a production hall is subject to large seasonal fluctuations. The extent of these fluctuations depends on the individual case. Based on empirical values, a typical temperature range between +20 °C and +35 °C is assumed below. This temperature range is distributed over the year according to the monthly average values in Germany for 2020 (source: DWD).

Figures 2a and 2b show the resulting temperature curves in the model. The aforementioned weather data (outdoor climate) is shown in black, the hall temperature in orange and the maximum temperature in the control cabinet in red. The control cabinet under investigation is already known from Figure 1.

The left-hand enclosure is considered, which has no active cooling in the initial state. A power loss of 500 W is assumed for this cabinet. A maximum permissible temperature in the switch cabinet of +40 °C is defined as the control variable. If this temperature is exceeded in the switch cabinet, heat must be extracted from it by means of active cooling.