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The Clean Air Delivery Rate - CADR explained!

What does the CADR Level actually tell us?

CADR briefly:
The CADR (Clean Air Delivery Rate) is a Measurement that indicates how well the Air Purifier has conditioned the Air. It helps to compare the Effectiveness of different Devices that are offered on the Market. In a nutshell, the higher the CADR Level, the more efficient the Product is.

CADR is a Value that measures the Air that has been cleaned by the Air Purifier. This Value is determined by practical Tests of the various Devices in a standardized Room. This standardized Room is 28.5 m³ and manages to accommodate almost a lying Soccer Goal in itself

Fig. 1 A standardized Room with a Size of 28.5m³.

First, this Type of Room is cleaned very thoroughly before the Product Test and is then filled with a Specific Type of Particles in each case. Afterwards, the amount of Particles that were not filtered by the Device is measured during the respective Tests and later subtracted from the originally supplied Value. This allows the CADR Value to be calculated. This represents the most accurate Method to determine the different Air Purification Products Products directly with each other. Aspects such as the Performance of the Air Purifier, the varying Size of the Vents, and the Filters installed in the Device play an important role during the Tests, but in general, the higher the CADR Value, the better the Device. However, not all Particles that contribute to Air Pollution are the same Size, which is why the Test must distinguish between Smoke, Dust and Pollen Particles and examine them separately from each other. Smoke Particles have a Size of approximately 0.09 - 1.0 Micrometers, Dust Particles have a Size of 0.5 - 3 Micrometers and Pollen Particles are in the Range of 5.0 - 11 Micrometers.

Fig. 2 Illustration of Particle Size

Despite the different Sizes of the Particles, although it seems only logical that large Particles can be filtered more easily, the Rate of Filtered Particles often turns out to be the same. This is due to the fact that larger Particles, such as Dust or Pollen Particles, are heavier due to their Size and can therefore adhere to Surfaces and Walls more easily. To provide better Filtration of small Particles, slower rotating Fans are often used. Since a slow intake Speed in turn gives the large Particles more time to settle on Surfaces, however, the "low" Filtration Level of large Particles Results in all the better Filtration of small Particles. When and why a HEPA-Filter or an ETA Filter is sufficient, it is here further explained

Pro Tip: The CADR Rating measures only the Efficiency of the Product and the Noise/Disturbance is not a Factor in this. Depending on where the Product is used, you may be able to reduce annoying Noises by purchasing a larger Product that runs at a lower Level. 

How does the HEPA Filter actually work?

Everyone promotes it, but almost no Buyer knows exactly what a HEPA Filter is and why it is so important for Air Purifiers and Filtering Devices. Named Filters achieve a particularly high Degree of Separation through the clever Application of physical Properties, and with them provide a reliable Result. By making use of the following Processes, HEPA Filters now even achieve a Separation Efficiency of 99.995%..

Inertia Effect

Since the Fibers inside the HEPA Filter are not arranged systematically, the Air does not flow through in a straight line and it has to make its way through the Thread Maze of the Filter Fabric. Particles have a certain Inertia due to their Mass. If such a Particle cannot follow the Movement of the Airflow due to its Mass, it will drift away and be intercepted by the Filter.

Explanation using the Example Car:

If you drive a Car too fast around a Curve, you don't manage to make the Curve and the Weight of the Car pushes the Car further straight ahead. This is exactly how Particles behave in the HEPA Filter. The Fibers in the Filter are randomly arranged, causing the Direction of the Airflow to change permanently, creating " Curves". The faster the Particles move, the easier they are captured.

Locking Effect

Smaller Particles tend to follow Air Streams that pass very close to the Fiber. Often these will nestle close to the Filter Material so that the Diameter of the Particle is greater than the Distance of the Airflow to the Fiber.

Explanation by example:

You are driving on the Highway on the left Lane through a Construction Site. At a marked Lane Change, the maximum Width is pointed out. If there is a wide Vehicle on the other Lane, it is often difficult to pass and since Particles do not have Brakes, they would collide with the Vehicle.

Diffusion Effect

The smallest Particles (<1 µm) do not follow any Currents and are caused to vibrate by colliding with the Molecules in the Air. These then stick upon Contact with the Media Fibers. As the Particle Size increases and the Flow Velocity to the Fibers increases, the Chance of the Particles sticking to a Fiber decreases.

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