Fans used in air handling units (AHU), such as large air-conditioning systems or heat recovery systems, must meet continually rising engineering standards. Today, besides greater power density and lower noise emissions, the focus is primarily on achieving the greatest degree of efficiency possible. In light of rising prices in the energy sector there is no doubt that the search for more efficient products will continue.

This is the background of the new R63D2 series. The reason why the new series number differs only by a single letter from the existing R63A2 is due to the geometrical similarity of the two series. The R63D2 features the same number of blades and the ring contour ( in the blade duct ) as the R63A2. In addition, the two sets of blades are nearly identical.

One special characteristic of the R63D2 is what is called the diffuser. The figure shows a magnified image of the ring and circular blank diameter at the fan outlet. By way of illustration: a model 400 R63D2 has an outer blade diameter of 400mm, but the ring and circular blank are 450mm. This is referred to as a rotating diffuser, which is the reason for the "D". In terms of ventilation engineering, the diffuser acts as a "speed converter", which means it reduces the speed of the air leaving the wheel as a consequence of the continuously increasing surface and, hence, converts the dynamic pressure into useful static pressure. Moreover, this "additional distance" permits directing the outlet flow, which can then impact positively on the flow instability (noise).

However, the enlarged ring and circular blank result in more frictional surface and, hence, greater friction-related pressure loss. Therefore, the form of the diffuser must be optimized taking into account the overall wheel configuration.

During the development of the series, engineers made use of modern simulation techniques. For example, using a CFD program to calculate flow, they were able to visualize the flows to design aerodynamically optimal blades. The welded seam was also defined based on a structural analysis. This permitted considering not only the engineering aspects, but cost effectiveness as well.

The new series with 12 sizes from 250mm to 900mm features:

• Very high degree of efficiency of as much as 75 % (for the 900 wheel)
• Very high power density
• Low noise emissions and a pleasant spectrum of frequencies
• Substantial fan-wheel strength
• Also suitable for external rotor motor

Dr. Y. Xia