Ventilation Introduction

Simple facts:

1. Fan size (i.e. diameter of impeller & outlet)
2. Duct and the way it is installed

Smaller duct = greater resistance to airflow.
More bends = greater resistance to airflow.
Longer duct runs = increasingly reduced airflow.

Wrinkled ducting causes turbulence and reduces airflow

Smoother, extended ducting allows smooth, increased airflow

3. Fan type

Centrifugal Flow:
Pressure developing fans which achieve good flow against the resistance created in a ducted system.
Particularly useful in venting areas like internal bathrooms/ laundries, multi-room extraction systems, heat-transfer systems, etc.

Mix Flow
Powerful in-duct mounted fans, designed for applications that require high air flows, with low relative noise.

Axial Flow:
Suitable for wall, window and roof applications where they can extract directly to the outside. Short duct runs are an option but the length of duct should be limited.
e.g.

• 100mm dia : 2-3m length
• 125mm dia : 3-4m length
• 150mm dia : 4-5m length

Compare Centrifugal Against Axial Fan Performance:

• SF100 (axial) vs an SF200 (centrifugal) fan
  The starting point is the free air performance of 23l/s for the axial and 31l/s for the centrifugal. As duct is added to each of these fans, this increases the pressure (Pa) and decreases volume of air moved. From the below example you can see that at 20Pa of pressure the 100mm axial fan airflow has stopped whereas the 100mm centrifugal fan is still moving 29l/s!

SF100 & SF200 PERFORMANCE GRAPH

• ID150 (axial) vs a MAN150 (centrifugal) fan
  The starting point is the free air performance of 89l/s for the axial and 115l/s for the centrifugal. As duct is added to each of these fans, this increases the pressure (Pa) and decreases the volume of air moved. From the below example you can see that at 120Pa of pressure the 150mm axial fan airflow has stopped whereas the 150mm centrifugal fan is still moving 102l/s!

ID150 & MAN150 PERFORMANCE GRAPH