Many air filter manufacturers will extol the virtues of their aerodynamically designed profiles for improving a building’s energy efficiency. For facility managers, site owners and purchasing teams, the ability to conserve energy and consequently make cost savings, is sure to appeal in the search for their building’s next air filter.
But are these claims that profile shape can positively impact air flow in air filter systems true?
According to leading climate technology and air filtration company Delbag GMBH, it’s all a myth.
Thinking outside the box
Earlier this year, Delbag set out to create new compact filter frames of its filter elements with the intention of finding out which profile shape provides the best aerodynamic solution.
The air filter in question has numerous applications, with the frame being used in air treatment systems sold to non-residential buildings to improve air quality for its inhabitants, as well as in turbines to protect blades from erosion, and at manufacturing plants to prevent harmful toxins leaving the site. While all four applications are distinct in their purpose and filter paper quality, the frame – and subsequently the profile shape – are the same.
This filter already offered a number of unique selling points: it is fully cast to protect from leakage between filter frame and filter paper; it benefits from a large filtration surface; it is EN 1935 food safe vital; it is built in an external aluminium grid for safety purposes; and it provides energy class A at 3400 m3/h.
But Delbag sought to find a way to improve on the product’s already notable energy rating. For this purpose, four different inflow profiles for the plastic frame were designed. For the numerical investigations, CFD software was used to allow the calculation of velocity and pressure distributions in the filter elements.
According to Delbag’s product manager Thorsten Stoffel: “The profiles are made of plastic and are used to bring the filter paper into a certain shape. Typically, these profiles are not streamlined or aerodynamic. The air will hit the profile and then cause some turbulence before moving into the filter.
“A lot of our competitors have rounded or angular shaped profiles, claiming that this gives the air a more dynamic flow into the filter. When we thought about redesigning our product we also thought about what we can do with the profile to make it easier for air to enter the filter.”
The team came up with four different ideas and conducted aerodynamic simulations with their own simulation team at the company HQ in Germany. First, they simulated air flow with their existing profile product, before experimenting on a very round profile, one with an angular shape and a flat surface, one with a rhombus shape and shortened straight lines, and lastly, a half round profile. The simulation programme calculated pressure loss, and the air speed that was travelling through the filter to provide information on air flow and energy efficiency.
The results? None of the changes in profile shape made any difference.
“In our simulation we did not see any difference in results on all proposed profile shapes, whether it was round, flat or angular.” says Stoffel.
To back up their findings, Delbag ran a second simulation at an external environmental testing lab (IUTA), and they came to the same conclusion. Because the profile is outside of the filter, it has no part in the filtration process.
“What the IUTA recommended to us when designing a new filter frame was to use the profile that works best for the production process and to not worry about aerodynamics because it is not relevant to energy consumption,” Stoffel continues.
“A lot of companies claim to their customers that their profile is aerodynamically designed to save them a lot of energy and improve air flow into the filter. But this is all a myth. To save energy, there are a number of approaches you can take, but changing the geometry of the profile is simply not the key to saving energy.”
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