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The key to enclosure cooling

03 October 2012

Foolish as it may appear, many see the additional financial outlay of installing a fan to ventilate an electrical enclosure as simply just another cost to cut. Yet the overheating of expensive equipment through failing to provide active ventilation is by far the main cause of failure within electrical cabinets.

FPF, GF and FF series fan filter units

The cost of a proficient fan unit is near inconsequential when compared to the cost of the equipment, labour and interruption to replace an inverter for example. Furthermore, a cooler operating environment significantly increases the lifespan and energy efficiency of equipment as will protection from dust and water splashes (IP54).

The simple answer lies in a combined fan and filter unit, designed to provide cooling air that is free of both dust and splashed water and when required, shield against EMC/RFI emissions. Selecting a fan is often made to be more complicated and expensive than necessary with overblown software programs giving manufacturer specific solutions.

The main points of consideration are the maximum ambient temperature, the temperature that the equipment needs to be kept below and the equipment heat loss figures, the latter of which can be obtained from the equipment instructions. A simple equation can then be used to determine the airflow.

V = (F x kW)/T

where: V is the volume required; kW is the heat dissipation/heat loss; T is the allowable temperature increase inside the cabinet, and F is the heat transfer coefficient of air.

[An example: (3.1 x 1200)/15 = 248m³/h required airflow].    
Our figure for the heat transfer coefficient (F) of 3.1 in the above example is based on the application being at an altitude of between 1-100m above sea level. It should be noted that the physical properties of air such as the specific heat and density change with altitude.

Keeping things simple, the fan filter unit should be of the “click-fit type”, this speeds installation time and requires no tools.  The fitted fans should be of a ball bearing construction and not sleeve, and often neglected is the ease of which the filter media can be replaced. The cover should be easy to remove to access the filter media; if the mechanism is not straightforward then this risks the probability that it will not get changed. This will inevitably result in problems in the long run.

Axair Fans stock no less than three different ranges of fan filter types, “FPF”, “FF” and “GF” by Fandis. These units have chevron louvred panels to aid in the reduction of water and dust. They are available from 105mm to 325mm square, the largest unit being designed to filter air at a rate of 660cu.m/h. In a standard fan filter unit the fan sucks air into an enclosure, first through the louvre, then the filter. Warmed air then exits, through a filtered louvre, generally of the same dimensions as the inlet but larger if necessary to improve the flow rate. 

The “FPF” series, thanks to their specific design are compact and fast mounting. To meet the needs of modern enclosures these units have a low external profile to avoid obstruction and are of a simple “click-fit” mounting type. An integrated sealing gasket also provides secure dust and water protection. Conversely, when space inside of an enclosure is precious, adaptors are available for certain sizes. These adaptors allow the filters to sit in a semi built-in position in the enclosure which in turn reduces the internal dimensions taken up by the fan filter unit. 

In addition to this the “GF” range has the advantage of innovative mounting systems with jacks which accommodate both plastic and plate enclosures with thick wall applications. The “FF” fan filter is the latest series offered by Axair. With an array of features this fan filter provides yet another solution to enclosure cooling. The “FF” range offer a fast mounting tool-less system which allows the unit to be easily clipped onto the enclosure. 

Each fan filter available is simple to fit and available in a variety of standard voltages both in AC and DC. Enhanced protection is available to IP55 along with EMC/RFI variants. The standard colour is RAL 7035 for all units. However, the “FPF” range can also be supplied in two further colours upon request. These colours are RAL 7032 and RAL 9005 (Jet Black) which certainly stands out. 

With long life shielded self-lubricating ball bearings every unit is available in standard air flow or reverse air flow. Standard flow introduces air into the cabinet while reverse air flow extracts air from the cabinet. Where the required minimum flow rate is not available, an enormous range of axial and centrifugal fans are available to choose from. In extreme cases it is possible to take a high performance fan and use it in conjunction with a number of standard filters, sized to achieve the ideal heat dissipating airflow.

Roof mounted units with top covers are available for both indoor and outdoor installation. The outdoor models are supplied with weather protection in the form of butterfly shutters that close under gravity during periods of system inactivity.

There is an answer to every problem, of enclosure ventilation, but at the extremes there is a need to utilise or combine standard products to make special solutions. Axair Fans also offers an extensive range of thermal management equipment for electronic and electrical enclosures, including standard and changeover thermostats, hydrostats, PTC heaters and lights to aid your thermal management.

Article supplied by Axair Fans UK.










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