1. Flow rate: If the system gives the mass flow rate of the gas, it is necessary to convert the mass flow rate of the gas into the volume flow rate under the standard state of the fan. If the system gives the volume flow of gas, the volume flow of the fan under the standard state is the same as the volume flow under the working condition.

  2. Pressure: According to the given or calculated working condition density, the working condition pressure is converted to the pressure under the standard state of the fan. If the fan has an air intake box or muffler, the pressure loss needs to be considered, which can be calculated or budgeted, and the estimated loss is generally between 100-300Pa.

   3. Density: If the density is not given, it is necessary to calculate or convert the density of the working gas according to the working conditions of the fan, such as altitude, local atmospheric pressure, working temperature, and standard density of the gas.

Next, it is necessary to calculate the specific speed, which is the main basis for judging the high/medium/low pressure of the fan. Substitute the performance parameters and speed converted into the fan standard state into the calculation formula of the specific speed (the formula is shown in the figure), and different specific speeds can be obtained according to different speeds. The first-order specific speed is the basis for the single suction fan; The second-order specific speed is the basis for the double-suction fan.