AIRFLOW RATE 

• Defined as the air volume required to be extracted or supplied into a room during a given period.
• Several methods can be used to calculate the required airflow:

CHOICE OF FAN 

The fan selection must consider parameters such as:

• Type of premises - industrial, commercial, domestic
• Nature of the air and its characteristics - clean air, air & dust or grease, special fluid (gases)
• Nature of the installation - supply and extract, wall fan, roof fan, ducted systems, position of the air entries, particular conditions
• Requirements of air flow and pressure drop
• Acceptable sound level in the room and externally
• Type of mains supply - single phase, three phases, voltage, frequency
• Other parameters may be considered for the selection such as dimensions, speed controllable motors, mounting accessories etc. 

THE FAN LAWS

• These laws enable you to change the aerodynamic parameters:

CONVERSION TABLE

PRESSURE DROP

• To obtain airflow in a ducted system it is necessary to overcome the resistance of the system:

           - due to friction in the duct length
           - due to the features of the system (bends, cross-section changes, filters, louvres etc.).

• These losses must be calculated accurately to select the correct fan and to give the airflow required

SOUND LEVEL

• In the catalogue, the sound level specified in the performance guide is a pressure level generally measured at 1,5 metres from the inlet for centrifugal fans, and at a distance equal to 3 times the impeller diameter (with a minimum of 1,5 m) for the axial flow fans.