Cooler cabinets at less cost

24 September 2017

Suzanne Gill recently found out about the energy saving benefits of an innovative passive air cooling solution for control cabinets.

With its LSC-AirSTREAM wiring system, LÜTZE has looked outside the box to develop a passive control cabinet cooling solution which focuses on the principle of ‘intelligent air guidance’ for a technically and economically ground-breaking thermal concept within control cabinets. Nigel Broad, managing director at Lütze Ltd, said “Components and power electronics in control cabinets are becoming increasingly smaller and more efficient. However, their heat dissipation losses are not reducing at the same pace. In addition, an increasing number of components are being packed into ever more compact control cabinets which has resulted in the heat inside the cabinet consistently increasing. This has led to a requirement for the use of high-performance, but energy-hungry, cooling units for cabinets.

Because active measures for control cabinet air conditioning - for example a roof-mounted cooling or front-mounted cooling unit - are so costly in terms of energy usage, interest in passive cooling methods is increasing. The Green Carbody Alliance, for example, a scientific initiative under the leadership of Volkswagen AG, has been able to verify that energy savings of up to 23% can be realised using the LÜTZE LSC AirSTREAM control cabinet system which means in some cases additional cooling can be dispensed with”.

The Green Carbody Alliance
Control cabinet manufacturers working as part of the Green Carbody Alliance, have also worked tirelessly to develop air conditioning units which are able to provide cool air to meet specific cabinet requirements at minimum cost. When these active cooling solutions are employed alongside the passive LSC-AirSTREAM wiring system the Green Carbody Alliance says that energy savings of up to 50% can be realised for cabinet cooling. 

The ever closer proximity of components within the control cabinet means that the cold air flow from active cooling systems is often not able to flow sufficiently through the areas between the components which leads to ’hot spots’ within the cabinet. If, for design reasons, it is not possible to spatially uncouple components in hot-spots, and if the reduced air flow exacerbates the heat problem, localised temperature levels of over 45°C can be reached which results in gradual thermal fatigue that can lead to premature component failure.

Broad explains: “The LÜTZE LSC AirSTREAM control cabinet system was designed to offer a solution for the targeted ventilation of such hot spots. Instead of the usual wire combs, its specially designed AirBLADES are inserted into the 50mm grid of the webs. At first glance, an AirBLADE looks similar to an aeroplane wing. It is designed to ensure that the air is not swirled around at its trailing edges which would cause the air flow to peter out. Instead, it is possible to accurately control the air flow and individual hot spots can be cooled to allow the operating heat in the control cabinet to be dissipated both selectively and generally."

Making passive solutions work
To make the passive cooling solution work to its best advantage LÜTZE advises that some design issues should be given careful consideration. It is necessary to ensure that no cumbersome components prevent the undisturbed inflow of cold air into the control cabinet interior and the extraction of warm air from the control cabinet interior. 

Components with high levels of heat dissipation should be placed close to the cold air intake. Correct component placement is especially important for the air conditioning variant with front-mounted cooling unit frequently to be found in practical use. For this purpose, the LÜTZE LSC AirSTREAM wiring system generates an optimised air circulation inside the cabinet. It is a modular aluminium frame, into which a further level is used at the bottom of the control cabinet for the wiring. 

In contrast with conventional cabinet constructions, no cable trunking is used. A ‘chimney effect’ is formed behind the LSC wiring frame and this dissipates hot air, depending on the cooling unit used. Ideally, cold air is guided downwards to the rear of the cabinet and then to the front and upwards again. This effect is improved on the new LSC AirSTREAM through the use of cable holders on the rear side of the wiring. In this way, the wiring becomes more compact and does not interrupt the air flow. 

Ambient temperature considerations
Ambient temperature is another factor that can have a major influence on the heat in the control cabinet interior. If the control cabinet air conditioning takes place with ambient air as the heat sink – as in the case of the free cooling or in operation with the air/air heat transmitter – the result will be increasingly high air temperatures within the control cabinet in comparison with the ambient temperature. The control cabinet interior temperatures will not naturally drop below the ambient temperature. Cooling of the control cabinet interior temperature below the ambient temperature is theoretically possible through the use of air conditioning units or air/water heat exchangers. However, in this case, heat is carried in, against the original intention, via the exterior surfaces. 

It is important to note that, for practical application, having a lower temperature inside the control cabinet than outside is inefficient and that the lower the ambient temperature surrounding the cabinet, the lower the expenses for air conditioning will be so it certainly makes sense to consider first whether it is possible to lower the ambient temperature, in particular if several control cabinets are put into operation. 

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