VENTEX® Ventilation Fans

An Axial fan has its motor located in the middle of the fan casing, and the airflow passes around it. A centrifugal fan has its motor located to the side of the fan casing, with a ‘snail’ shaped impeller. Typically a centrifugal fan will provide less airflow but at higher pressure than an axial fan with the same size motor.

Axial fans are better for moving high volumes of air over short distances, whereas Centrifugal fans are better at maintaining high pressure over long duct runs. Despite a lower flow rate, centrifugal fans create a steadier flow, resulting in a significantly higher static efficiency. Centrifugal fans are also typically quieter than axial fans, and even with attenuators fitted are more compact. The best fan to use therefore depends on the requirements of the project.

For railway tunnels, centrifugal fans are often the preferred option as they can be situated outside the tunnel, ensuring that they do not get in the way or block access for vehicles and machinery. Centrifugal fans also maintain high pressure over long duct runs, so they can deliver clean air deep into long tunnels; however, we have also supplied large, high power axial fans, for several tunnel projects.

Typically, Centrifugal fans are the best fans to use for basement ventilation, because they are quiet, compact and perform well even when using long duct runs or duct runs with multiple bends (as is often required to be the case), however we have also used our largest high power Axial fans to force fresh air into many top-down construction basement projects.

Each basement project is unique; different activities, access points, depth and volume of excavation etc. and therefore requires a tailored approach.

In section 3 of the government guidance titled 'Transmission characteristics and principles of infection prevention and control', Public Health England explain that;

"A single air change is estimated to remove 63% of airborne contaminants, after 5 air changes less than 1% of airborne contamination is thought to remain".

The number of air changes required will depend on the environment you are working in and the activities you are conducting; the higher the airborne risk, the more air changes required.

In sensitive environments, Public Health England recommend 6 - 12 air changes per hour.

This is a very broad question and the answer depends on what type of environment you are working in, the size of the work space, the types of activities you are undertaking, and what contaminants you are dealing with (eg. dust, fumes, DEEEs, gases etc.).

However, generally speaking there are two ventilation methods for controlling airborne contaminants on site; supply and/ or extraction. Positive pressure ventilation systems can be used to supply a constant flow of clean air into a work space which will displace any contaminated air. Alternatively, if you have a specific activity that is generating the airborne contaminants, a local exhaust ventilation system (portable LEV) can be used to extract and filter the contaminated air out of the work space. Quite often, a combination of the two methods will work well; use an appropriate extraction system with capture hood to capture and extract the contaminants at the source of the activity, then force in clean air to dilute the residual contaminants in the air.

Learn more about best practice ventilation