3.5.4. Characteristic Definition

ISO 5801 specifies the test conditions, the evaluations and the fan characteristic curve presentation forms of the measurement results. It therefore applies only to separate fans, which are usually offered in catalogs for general installation conditions, but not to fans which are part of different inlet variants with elbows, edges, guard grilles and similar individual resistances that cause an inhomogeneous velocity distribution (e.g. swirl) have a direct influence on the fan performance. They cause so-called "system losses" in the fan itself. These losses cannot be determined theoretically in all details and are additionally dependent on the fan design. In the case of correspondingly unfavorable inlet and outlet flow conditions, the fan standard characteristics determined on a standard test rig in accordance with ISO 5801 cannot be assumed. A distinction must be made here between fan, unit and system characteristics.

In the punker catalog characteristic curves or characteristic curve fields, only the standard fan characteristic curve according to the DIN/-ISO standard test bench with a flow-favorable installation situation can be shown, since punker is only the manufacturer of fan impellers.

In designs such as a double inlet centrifugal fan, it is unavoidable to keep the inlet cross-section free of design elements such as through shaft, bearings, belt slides, guard grilles, etc. The losses caused by this are not included in the pure characteristic curve of the fan wheel. The resulting losses are not included in the pure characteristic curve of the fan impeller. They depend on the above-mentioned design elements and are therefore to be considered as unit losses (see Figure 3.5.4.). In the case of the double-flow design (D), a reduction in performance must therefore be expected depending on the intake blockage

Figure 3.5.4: Characteristic curves with blockage

Key

q_{V,I} : volume flow at fan inlet, in cubic meters per second 
p_{fs} : static fan pressure, in pascals

Practical value for the upper underpower:

 \Delta p=\left(0,25-1,0\right)\cdot p_d

For complex installation situations, tests in the original setup are unavoidable. Depending on the application, we at punker offer you a laboratory with different types of test stands for this purpose.