The test case fan is equipped with 3HS20 InfiniSpring®-springs and a 2.2 kW electric motor, which is controlled via variable-frequency drive. The motor nominal speed is 1440 rpm. The fan is used in air handling units and typically equipped with rubber elements. This article focuses on validating InfiniSpring®-spring selection based on the fan weight data. Fan with 3HS20 InfiniSpring® is shown in Figure 1 below.
Datasheet Data for 3HS20 Spring
According to technical datasheet 3HS20 spring is for nominal load ranges between 15-20 kg and for rotational speeds above 755 rpm. Maximum vertical natural frequency is less than 11.7 Hz, Table 1 below.
Table 1. Maximum vertical natural frequencies when using nominal load range.
Natural Frequency Validations
The vertical natural frequency was measured to validate the limit value 11.7 Hz. The measured vertical natural frequency result is shown below in Table 2 together with the datasheet limit value.
Table 2. Measured vertical natural frequency.
In order to comply with the data sheet value, the measured value needs to be below the datasheet frequency 11.7 Hz for vertical natural mode. Based on the 9.5 Hz measurement result we are clearly on a safe side. It is to be noted that the test case fan 3HS20 InfiniSpring® is for a load range of 15-20 kg and the spring load is 20 kg. This means that 15 kg spring load would give vertical natural frequency of approximately 10.5 Hz and the result would be safe with lower load.
Based on the measurement the vertical mode frequency for the test case fan 3HS20 InfiniSpring® is from 9.5 Hz to 10.5 Hz and vertical mode frequency is always safely below the datasheet value 11.7 Hz. Weight data can be used very safely for the spring selection.