Axial fans are a type of fan designed to move air in a direction parallel to the axis of rotation of the fan blades. They are the most common type of fan used in domestic bathrooms, particularly for wall-mounted installations. These fans are ideal for short duct runs (less than 5 metres) and are typically used to provide ventilation in wet rooms such as bathrooms, en-suites, and WCs.
Key Features:
- Airflow Direction: Air moves parallel to the fan’s axis of rotation.
- Design: The fan impeller or blades are specifically shaped to maximise airflow efficiency while minimising noise.
- Operation Options: Axial fans are available with various operational mechanisms, including:
- Timer-Controlled: Runs for a set duration after being switched on or off.
- Humidistat-Controlled: Activates when a pre-set humidity level is reached (e.g., in bathrooms).
- Pull Cord: Operated manually by pulling a cord.
- PIR (Passive Infrared): Activates when motion is detected in the room.
- Light-Switch Controlled: Turns on when the room light is switched on.
Voltage Options:
Axial fans are typically available in:
- Standard 240V: Suitable for general use.
- SELV (Safety Extra Low Voltage) 12V: Designed for use in Zones 1 and 2 of a bathroom where safety regulations require low-voltage systems.
Limitations:
Axial fans are not suitable for long duct runs exceeding 5 metres. Their efficiency decreases significantly in such applications due to the increased air pressures within the duct, which they are not designed to overcome. For longer duct runs, centrifugal fans or mixed-flow fans are more appropriate.
Applications in Real-World Settings:
- Bathroom Ventilation: Axial fans are commonly installed in bathrooms to extract moist air and prevent condensation and mould growth. For example, a humidistat-controlled axial fan may activate when steam from a shower raises the room’s humidity.
- Retrofit Projects: In retrofit scenarios, axial fans are often used as a cost-effective solution for improving ventilation in older properties with limited ducting requirements.
Example:
In a small family bathroom with a short duct run leading directly outside, an axial fan with a timer and humidistat would be an ideal choice. It would automatically activate during a shower, extracting moisture-laden air and reducing the risk of damp and mould.