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The Significance of Velocity Pressure in Selecting Fume Extraction Exhaust Fans for Ducted Systems

In fume extraction systems, ensuring the safe and efficient removal of hazardous airborne contaminants is the primary task. Properly designed exhaust fans are instrumental in achieving this objective. Among the critical factors to consider during the fan selection process, velocity pressure stands out as a key parameter that directly influences the performance and effectiveness of a fume extraction system.

In simple terms, velocity pressure is the pressure created by the fast-moving particles in a gas because of the speed it moves. Velocity pressure directly influences the airflow rate in a ducted system, the higher the velocity pressure, the faster the air moves through the duct. If the velocity pressure is too high, it may lead to excessive turbulence, noise and pressure loses throughout the duct, therefore it is a useful figure to determine the appropriate duct sizing and design. If velocity pressure is too low, it could result in inadequate airflow. As air moves through the ducted fume system, it encounters friction and other resistance, causing a pressure drop. Velocity pressure is one of the factors contributing to this pressure drop. If systems are designed poorly, they will consume more energy to maintain the required airflow. Optimising the system design can lead to energy savings and more efficient operation. Understanding velocity pressure helps engineers and specification designers to create better systems for things such as ventilation systems and air conditioning, making sure that air flows efficiently and safely through pipes and ducts.


Why does velocity pressure hold such significance when choosing exhaust fans for fume extraction systems with ducting.

  1. Optimal Airflow Rates: Velocity pressure directly impacts the airflow rates within the ducting system. The airflow rate is crucial in fume extraction as it determines how quickly contaminated air is removed from the workspace. By choosing fans with appropriate velocity pressure capabilities, engineers can ensure that the system achieves the required airflow rates to efficiently capture and remove hazardous fumes.
  2. Minimising Pressure Loss: Ducted fume extraction systems can incur pressure losses due to friction and resistance as air flows through the ducts. Velocity pressure plays a crucial role in mitigating these losses. Fans with sufficient velocity pressure capacities can overcome these losses, ensuring that the desired airflow is maintained throughout the ducting network. Minimising pressure losses helps maintain the system's efficiency, reduces energy consumption, and prolongs the fan's lifespan.
  3. Sizing and Design of Ductwork: Properly sizing and designing the ductwork is vital for the effectiveness of the fume extraction system. Velocity pressure considerations aid in determining the appropriate dimensions of the ducts. A well-designed ducting system that accounts for velocity pressure ensures smooth airflow and minimises turbulence. This reduces the likelihood of contaminants settling or recirculating within the workspace, enhancing the overall efficiency of the fume extraction system.
  4. Ensuring Adequate Capture Velocity: Capture velocity refers to the minimum air velocity required to effectively capture fumes and prevent them from escaping into the surrounding environment. The velocity pressure of the exhaust fan must be sufficient to achieve the necessary capture velocity, which varies depending on the specific contaminants and their source. A fan with inadequate velocity pressure may fail to capture the fumes effectively, leading to compromised worker safety and environmental compliance.
  5. Managing Air Distribution: Velocity pressure considerations extend beyond the fan outlet and into the workspace. Proper airflow distribution is essential to ensure that fumes are effectively extracted from all potential sources. By selecting exhaust fans with appropriate velocity pressure characteristics, engineers can optimise air distribution within the workspace, reaching every critical emission point and guaranteeing comprehensive fume extraction. Velocity pressure is a crucial factor to bear in mind when selecting fume extraction exhaust fans for ducted systems. It directly influences airflow rates, pressure losses, duct sizing, and the effectiveness of contaminant capture. By choosing fans that align with the specific velocity pressure requirements, fume extraction systems can be efficiently designed, ensuring worker safety, regulatory compliance, and a healthier work environment for all occupants.

>> A Complete Guide to Fume Fan Selection in Fume Extraction Systems >>