Feature Air movers Thinking inside the box!
Roy Sexton, fan product manager at Aerco, considers enclosure cooling and discusses significant new developments in AC fans
Tighter packaging increases system pressure while increasing the quantity of heat to be dissipated – and it is this resistance to airflow that remains the biggest single issue. Designers have experimented with Peltier thermoelectric coolers, heat pipes and water-cooling with only qualified success. But, the tried and tested equipment fan, in its various guises, remains the favoured method.
I Calculating the airflow
Performance data from the fan manufacturer is required to calculate the required airflow, but it must be remembered that airflow is always quoted in free air and the pressure drop across the enclosure has a vital bearing on fan performance. It is possible to measure pressure drop by using a venturi tube and anemometer, but this is a complicated task and may require specialist assistance. In reality, an intelligent and experienced interpretation of the fan performance curve will define the duty-point of the fan from which the airflow that the fan will achieve at any given pressure can be established.
Ensuring maximum cooling
Enclosures come in all shapes and sizes, each with its indi- vidual cooling requirement. In addition, depending on the application, operating conditions will vary from benign, air-conditioned offices to the most hostile industrial or commercial environment.
The number of fans and their positioning within the enclosure is critical to ensure that the optimum air path and maximum cooling effect are achieved. It is also important that specific hot spots are identified and cooled effectively. Whatever the final layout, it is highly recom- mended to draw ambient air into the enclosure and exhaust warm air, ensuring cool air is drawn over the bearing of the fan, thus optimising its life.
Selecting the right fan
When choosing a fan the fundamental differ- ences between types must be taken into account. In broad terms, axial fans give high volume but do not work well against high system pressure; blowers provide less volume but perform better at higher pressures; while air wheels deliver high volume at high pressures. Aerco supplies axial, flat axial, centrifugal blowers, single and double inlet, skeleton fans, cylindrical air wheels and backward curved impellers – in fact the list is too long to discuss at length here. An experienced cooling special- ist will establish the best choice very quickly by analysing the space available, the air volume required and the anticipated system pressure. IP rating is an important factor, as is the projected life of the fan, and this dictates the choice of bearings. Sleeve bearings are less expensive and quieter than ball bearings, but ball bearings provide maximum life while modern hybrid bearings can provide a useful compromise.
Enclosure & Safety Solutions SUMMER 2013
t is a harsh fact of life that designers of electronic systems are continuing to pack more capability into smaller assemblies, and this presents an ever-increasing problem for the heat management engineer.
AC benefits Until recently, the vast majority of fans used in enclosures were DC due to their efficiency, flexibility and controllability. Recent developments in AC fan technology, however, have delivered a major revival in the application of AC fans. The American fan manufacturer, Sofasco, a new exclusive franchise for Aerco, has intro- duced a range of frequency switching fans that has AC power input but incorporates circuitry that delivers DC power to the fan motor.
This technology provides many advantages over conventional AC fans, having long life, high reliability, low power consumption and a wide input voltage range. Most importantly, thanks to a patented design that reduces the hub area and increases the size of the impeller, it provides double the airflow of a conventional AC fan of a similar size. Frequency switching fans also provide multi-function controls that can be used in ‘intelligent’ cooling systems, a hitherto weakness in AC fans. With the cost of failure due to overheating being catastrophically expensive and the growing requirement to run systems at optimum temperatures with maximum operating efficiency, such systems are becoming increasingly popular, and this is a major step forward for AC fans.
Although marginally more expensive than traditional AC fans they will, through their increased performance levels, energy efficiencies and controllability, not only be specified to replace existing AC fans but will rival DC fans for use in enclosures and other areas where DC fans have been favoured. Although there are numerous waterproof DC fans, there are comparatively few AC. The recently introduced Adda AA1282 range allows designers to use readily available AC supplies to power a fan that provides IP55 protection levels and has passed stringent salt-water spray tests. This range is likely to prove a viable contender for cool- ing enclosures used in freezers, refrigerated rooms, food processing plants, and applications that use spray-down cleansing techniques.
Plan ahead
Whatever the shape and size of the enclosure and its application, an efficient, cost effective heat management system is vital to optimise system performance, reliability and life cycle. Planning for heat management early in the design stage is just as important as choosing the correct type and positioning of the fan assembly itself. There are many fan products to choose from. If you are finding keeping cool is not as simple as it sounds, it might be a wise move to seek experienced advice.
Aerco T: 01403 260206
www.aerco.co.uk
Enter 260 Roy Sexton
Left: The AE 547
Sofasco frequency switching fan, which is available from Aerco
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