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Abstract

The paper will present new concept of centrifugal fan regulation with use of variable blade length system. Higher demands regarding low energy consuming devices do not omit fan what is underlined by internal regulations (e.g. EU Regulation 1253/2014). Regulation of fan is required in each system when constant value of flow and/or pressure cannot be ensured. Application of frequency inventers seems to be the most efficient method of regulation in case of centrifugal fan but has also some drawbacks. It requires additional power supply infrastructure. If fan is larger, costs of whole system increases. In case of large fans this costs are very high and change of rotational seed causes problem, since high inertia forces due to large rotating mass exist. Also, what is sometimes forgotten, costs of reactive power in such cases are very important from economical point of view.
Alternatively, especially in case of larger centrifugal fans, implementation of fan with variable geometry can be solution ensuring operation in wider range with the highest possible efficiency. The concept described in the work is based on fan with variable blade length. Change of blade length causes change of impeller diameter and as a result flow characteristic of fan. In the article analytical description of such fan will be presented. What is more result of tests on real object with new solution will be presented to show fan performance curves within whole range of regulation.
As showed currently done analytical calculations and CFD calculations, such solution can be an alternative to centrifugal fan with rotating end part of blades as well. Even if many difficulties exist in case of application of such system, this solution does not require additional costly power supply components and seems to be reasonable for big fans.