The importance of low pressure drop in an energy efficient ventilation system

Pressure drop is a recurring term in our technical documentation and product descriptions. Why, you may ask? Well, pressure drop can be a source of wasted energy and is an important parameter in determining the overall running costs of a building’s ventilation system. In this blog post, we’ll try to explain pressure drop in a simplified way, how pressure drop data is used in ventilation design and why low pressure drop contributes to a more energy efficient ventilation system.  

Imagine you are a cyclist in a race on a beautiful summer’s day. You cycle along, feeling the breeze at your back and the excitement of the crowds cheering you on. But then you turn a corner and find yourself cycling up a narrow, bumpy alley. There are tall buildings on both sides of the street and the air feels still and stagnant. Your feet feel heavier and heavier, and you start to feel slow and tired as your body uses more and more energy to move forward.  

Although not the same – it’s a bit like what happens in a ventilation system when there’s a pressure drop.  

So, what does pressure drop mean in practice?  

Just as the cyclists feel the resistance as they ride up the narrow and bumping alleyway, the air flow in a ventilation system loses power as it moves through small or obstructed ducts. 

“Pressure drop in a ventilation system refers to the decrease of power in the air that occurs as the air flows through the ducts and other components of the system. As the air moves it loses some of its pressure due to friction against the ductwork. Any changes of flow direction, splitting or merging of flows, as well as any change of size cause resistance, which will vary depending on air velocity and shape. The higher the resistance in a system, the more power the fan must apply to get the air moving”, explains Lars-Åke Mattson, one of Lindab’s development managers. 

The use of pressure drop data in ventilation design 

Typically, Lindab ventilation components are documented with a pressure drop table, which shows the pressure drop of a particular component in a system at different air flow rates. In the same way that cyclist carefully selects aerodynamic cycling gear before the race, the system designer must calculate the pressure drop of a ventilation system as accurately as possible and select components to minimise pressure drop and ensure efficient use of the fan with precise data.  

“The component data is used to calculate the pressure drop of an entire ventilation system, which is approximately the sum of all the individual pressure drops along the air path in the system – from the fan to the terminal”, explains Lars-Åke   

The pressure drop data of the system enables further calculations and to select the right fan or air handling unit.  

“Pressure drop data is an important part of the total amount of energy required by the fan to move the air through the system. The higher the pressure drop of a system; the more energy is required for the fan to move the air”, Lars-Åke points out.  

Low pressure drop for energy efficient systems and better indoor environment 

Considering pressure drop in both new and older ventilation systems is a useful way to manage the airflow and the fan energy consumption for a more efficient system. 

“Designing ventilation systems with low pressure drops also has a positive effect on the system noise levels. This will further improve the indoor environment and reduce the cost of silencers”, says Lars-Åke.  

So just as the cyclist must prepare for the race, knowing the terrain and adjusting the pace accordingly, to regain their flow and carry on with ease, ventilation designers and facility managers need to be prepared and aware of the pressure drop in a ventilation system to avoid excessive resistance, inefficient performance, and higher running costs.  

For more technical information on pressure drop, take a look at our general information and theory

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