The Minipleat Filter Construction

Why is a panel filter with MiniPleat construction the best choice?

The development of air filter designs has undergone significant changes in recent decades. New textile materials and manufacturing processes have appeared on the market, which have made it possible to achieve new filter properties as well as energy savings. In recent years, the entire industry has focused primarily on nanomaterials, which are experiencing a particularly strong boom in air filtration. We can therefore expect the development of new manufacturing processes and applications that these new materials can offer us in the coming years. If manufacturing costs can be reduced at the same time, nothing stands in the way of their wider application.
However, if we look at air filters that are already freely available on the market and are commonly used in ventilation systems, we can see clear differences here. These filters have different shapes, different dimensions, different textile materials are used for them, they differ in their manufacturing costs and, above all, in their filtration performance.

Pressure loss and separation efficiency
The pressure loss of a filter is one of the most important parameters, along with the filter's separation efficiency. Unfortunately, these filtration characteristics are interrelated and influence each other. So if we need a filter with a high degree of separation, a textile with a higher fiber density must be used to produce it, which means that they better capture pollutants from the air.
Such materials therefore have a higher material density or a higher basis weight. This increase in surface weight improves the separation efficiency of the filtration as we capture more pollutant particles, but at the same time the resistance of the material to air flowing through increases and the ventilation system has to provide higher performance. In general it can be said that it is not possible to produce an air filter that has a high separation performance and at the same time a very low pressure loss.
You may now be asking yourself how we can significantly reduce the pressure loss of the filter if we want to use filters of a higher filter class. The answer to this question is relatively simple - you have to r filtration surface work. This is precisely the basic and crucial parameter of any filter to work with.
For a more detailed explanation we cannot do without the Darcy equation and its intentional simplification, which describes the relationship between the filter area and the pressure loss:

Q = A Δp k k

where Q is the air flow (m³/s), A is the filter area (m²) and Δp is the pressure loss (Pa).

The constant k combines the filter strength (m), the dynamic viscosity (Pas) of the fluid and the permeability of the filter (mm²).
This equation applies to virtually any porous material, and its structure is described by the parameters contained in the constant k.
If we ignore other influences, such as the dynamics of the fluid and turbulence caused by the flow of air through the filter, it clearly follows from this equation that the relationship between the filter area and the pressure loss is linear.
With the same constant flow, if we e.g. For example, if you increase the filter area 10x, the pressure loss is also reduced tenfold. But how do we get a 10x larger filter into our ventilation system??

The filter construction called MiniPleat was developed for this purpose
This filter design was created as an alternative to pocket filters, whose pressure loss is low thanks to the large filter surface of the pockets, which means that filter media of higher filter classes can also be used without any concerns. The disadvantage of these pocket filters is the fact that they take up a lot of space in the ventilation systems due to the voluminous pockets, which means they are not suitable for compact systems such as those used in apartments or single-family homes. Pocket filters are therefore primarily used in systems with air flow rates greater than 500 m3/h. At lower throughputs, these filters are only used sporadically.

The MiniPleat construction offers high performance in a small areae
The term MiniPleat can be loosely translated from English as mini-pleat. It is a filter construction in which the filter media is mechanically placed into dense folds of a predetermined uniform height, with the folds then being fixed with a special hot glue. The distance between the individual folds is in the range of a few millimeters. This dense pleat design allows more filter media to be packed into a given filter dimension, significantly increasing the filter area and achieving a reduction in pressure loss.

An important parameter in this filter design is the number of folds per 1 m of length. This parameter is called fold density. The following diagram shows the relationship between the relative filter area and the fold density.

If we use a filter medium, for example For example, if you make a filter with MiniPleat construction and a height of 40 mm and 100 pleats per 1 meter of length, this filter has a filter area eight times larger than its actual size. The relationship between the number of folds and the filter area is almost linear. However, it must be noted that with very high fold densities, the area through which the supplied air flows is blocked, which reduces the usable area. This value is called the critical fold density.
 
The Technical University in Liberec carried out a test on two different filter media to investigate the influence of fold density on the pressure loss at an air flow speed of 5 m/min. The following diagram shows the influence of the pleat density on the pressure loss for two filter media with different surface density of the material (100 g/m2 vs. 35 g/m2) and a filter area of ​​20 mm.

It is clear from the diagram that the material with the smaller areal density experiences a significantly smaller reduction in pressure loss than the material with the higher areal density. The critical wrinkle density is reached at a value of around 150 m-1 for the material with the higher surface density. After this value is exceeded, the pressure loss begins to increase slightly again.
Nevertheless, by folding the filter medium, an up to tenfold reduction in pressure loss can be achieved with the material with a surface density of 35 g/m² and an up to thirteenfold reduction in pressure loss with the material with a surface density of 100 g/m².

All of the above facts clearly show that varying the filter area is the only possible way to achieve a reduction in the pressure loss of an air filter. The construction of the MiniPleat filter is based on this, which reduces the pressure loss many times over by placing the filter medium in dense folds. MiniPleat enables the use of filter media of a high filter class in air conditioning systems. This is one of the main reasons why the SafeLuft air filter range uses the MiniPleat design type to ensure high filter performance, a significantly longer service life thanks to a larger filter area and a lower pressure loss..

Literature and sources used
RUKATECH, sro : Internal documents
TU Liberec, Ing. Jakub Hruza, Ph.D.: Improving the filtration properties of fiber materials