How to design a tangential blower housing

by Lauria Avon,
Vice President of Technology for Eucania International Inc.
Featured in Applicance Magazine, October, 2003

Tangential blowers have often been overlooked because of their perceived low efficiency in certain applications and the misunderstanding of their proper use. However, they can be a solution to efficiently move air.

Tangential wheels generally find their best use in low-static applications (generally less than 0.5 in of static pressure), in applications where low noise is critical, and applications that are best filled by a uniform airflow over a wide path or air curtain. The many applications of tangential wheels include refrigeration systems where the wide, narrow band of air is most efficiently used to spread throughout an area; air purifiers where it is desirable to have a maximum surface of air pushing though a filter; and where any wide area needs to be cooled, heated, or have air flowing through it.

Tangential wheels are usually more efficient when a focused flow of air is required to cool or heat an immediate space. When used in this manner, the air does not have to travel long distances, but instead is used in the immediate surroundings such as in wood stoves and gas fireplaces.

One of the reasons that tangential wheels are quieter in comparison to a centrifugal-style blower is that for products with the same cfm rating, the air speed of the tangential wheel is much slower since the outlet area is much larger than that of a centrifugal blower. This can be seen as an advantage, because the large area of discharge of the tangential blower does not require additional diffusion, which would create losses and thus decrease efficiency.

When compared to double inlet wheels used in a double blower, tangentials will generally provide an equal or slightly increased cfm with the same motor.

Getting the Most Out of a Tangential Blower

Figure 1. Airflow pattern of a
tangential blower.
(courtesy of Whirlpool)

As seen in Figure 1, the airflow is tangentially in across the inlet area and tangentially out across the discharge area. The most efficient configuration is when this 90-degree change in direction can be utilized in the design of a product.

Ideally, if filters or coils are involved, tangential blowers should be used in a pull-through rather than a push-through manner. The inlet air speed is over a larger surface and, therefore, is lower than the discharge airspeed. This usually contributes to lowering the static in the system as well.

As discussed, tangential wheels prosper in low-static situations, so it would be a good idea to try to minimize the static in a system to best utilize the power of a blower. This can be achieved by minimizing the changes in direction of airflow within the application and using the 90-degree change within the tangential to its best by positioning the blower where the airflow is required to make a 90-degree turn. Also, funneling of the discharge must be avoided; it is better to reduce the discharge closest to the wheel than to slowly reduce the discharge area as shown in Figure 2.

Housing design is critical in blower performance (Figure 3). Some tips include:
  • For optimum cfm, A=0.60ø, B=0.85ø, C=0.60ø, E=F=0.07ø, G=15 deg, and HIJ should be a straight line. If a smaller outlet is necessary, it is better to reduce A first to a minimum of 0.45ø, then A and B together rather than funneling the outlet. Air will discharge following the 15 degree upward. If this is not desirable, for maximum discharge, the entire housing must be rotated-G should not be reduced.

  • Reducing A will affect cfm, but not air speed.

  • For noise control, dimensions E and F are critical, with F being the most critical. Reducing both E and F will increase cfm and noise level.

  • When using grills at discharge, the cfm will be directly reduced by the percent of area covered if the blower maintains the same wheel speed.

  • For applications where the motor is running below its maximum speed: when static of any kind is applied to the system at the discharge, the wheel will speed up to try and maintain the same cfm up to the maximum speed of the motor. This is a useful design feature that can be used in an application where static might build with time (as dust in a filter). If the initial motor is designed to run below its maximum speed, this leaves room for the motor to speed up and maintain its performance.

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