The resistance size of the folded frame combined filter is an important indicator to measure its performance, directly affecting the energy consumption and operational efficiency of the ventilation system. Its resistance (including initial resistance and final resistance) is mainly related to the following factors:
1. The characteristics of the filter material itself
Material and structure: The fiber density, diameter and porosity of different filter materials vary significantly. For instance, superfine glass fiber filter materials, due to their fine fibers and low porosity, have a stronger ability to block air flow, and their resistance is usually higher than that of loose materials such as non-woven fabrics or nylon nets. If the fibers of the pleated structure filter material are arranged in a disorderly manner, it will increase the flow path around the air flow, and the resistance will also rise accordingly.
Thickness: The greater the thickness of the filter material, the longer the path for the airflow to pass through, the higher the probability of collision and friction with the fibers, and the resistance accordingly increases. For instance, the filter material thickness of high-efficiency filters is usually greater than that of primary filters, and their initial resistance is also higher.
2. Filtration area and folding design
Filtration area: Under the same air volume, the larger the filtration area, the lower the air flow velocity that the filter material per unit area bears, and the smaller the resistance. The core advantage of the folded frame combined filter is that it increases the filtration area through a folding design (usually 5 to 10 times that of a flat filter screen), thereby reducing resistance. If the folding spacing is too small or the number of folds is insufficient, the actual effective filtration area will decrease and the resistance will increase significantly.
Folding shape: The uniformity and Angle of folding also affect resistance. For instance, if the angles of V-shaped folding are inconsistent or the folds are skewed, it will lead to uneven airflow distribution, excessively high local wind speeds, creating “bottleneck” areas and increasing overall resistance.
3. Air flow and wind speed
Air volume: Resistance is positively correlated with the air flow (or wind speed) passing through the filter, and usually follows the “square law” – when the wind speed doubles, the resistance approximately increases to four times its original value. For instance, at the designed air volume, the initial resistance of a certain filter is 50Pa. If the actual air volume exceeds the design value by 30%, the resistance may rise to 70-80Pa.
Air flow distribution: If the filter is not installed properly (such as the frame not being sealed tightly or the clearance with the air duct being too large), it will cause air flow short circuit or local excessively high wind speed, destroying uniformity and thereby increasing resistance.
4. Dust holding capacity and service life
During the operation of the filter, dust gradually accumulates on the surface of the filter material, blocking the pores and reducing the effective channels for air flow to pass through. As the dust holding capacity increases, the resistance rises. When the resistance reaches the “final resistance” (usually 2 to 3 times the initial resistance), the filter needs to be replaced. For instance, the initial resistance of the primary filter is approximately 30 to 50Pa, and the final resistance may reach 100 to 150Pa. The initial resistance of the high-efficiency filter is approximately 150-250Pa, and the final resistance can reach 300-400Pa.
5. Physical properties of air
Temperature and humidity: High temperatures will reduce the viscosity of the air and slightly decrease the resistance. In a high-humidity environment, if the filter material absorbs moisture (such as paper filter materials), it may cause the fibers to expand, the pores to contract, the resistance to increase, and even the filter material to deform and block the air flow channel.
The nature of pollutants: The particle size, density and viscosity of pollutants in the air will affect the dust holding speed. For instance, highly viscous cooking fumes and dust tend to adhere to the surface of the filter material, accelerating pore clogging and causing the resistance to rise more rapidly. However, large particles of dust may form “Bridges” on the surface of the filter material, which instead delays the growth of resistance (but reduces the filtration efficiency).
6. Outer frame and protective net design
The sealing performance of the outer frame, the material of the protective net and the hole diameter will indirectly affect the resistance. For instance, if the protective net is made of overly dense metal mesh, it will increase the air flow resistance additionally. The connection between the outer frame and the filter material is not tight, causing turbulence in the airflow at the gaps, which may also increase the overall resistance.
Summary
The resistance of the folded frame combined filter is the result of the combined effect of multiple factors such as the characteristics of the filter material, structural design, and operating conditions. In practical applications, it is necessary to select appropriate filter materials and specifications based on the design air volume and cleanliness requirements, and ensure that the system operates under low resistance and high efficiency by regularly replacing the filters (judged based on the final resistance).
1. The characteristics of the filter material itself
Material and structure: The fiber density, diameter and porosity of different filter materials vary significantly. For instance, superfine glass fiber filter materials, due to their fine fibers and low porosity, have a stronger ability to block air flow, and their resistance is usually higher than that of loose materials such as non-woven fabrics or nylon nets. If the fibers of the pleated structure filter material are arranged in a disorderly manner, it will increase the flow path around the air flow, and the resistance will also rise accordingly.
Thickness: The greater the thickness of the filter material, the longer the path for the airflow to pass through, the higher the probability of collision and friction with the fibers, and the resistance accordingly increases. For instance, the filter material thickness of high-efficiency filters is usually greater than that of primary filters, and their initial resistance is also higher.
2. Filtration area and folding design
Filtration area: Under the same air volume, the larger the filtration area, the lower the air flow velocity that the filter material per unit area bears, and the smaller the resistance. The core advantage of the folded frame combined filter is that it increases the filtration area through a folding design (usually 5 to 10 times that of a flat filter screen), thereby reducing resistance. If the folding spacing is too small or the number of folds is insufficient, the actual effective filtration area will decrease and the resistance will increase significantly.
Folding shape: The uniformity and Angle of folding also affect resistance. For instance, if the angles of V-shaped folding are inconsistent or the folds are skewed, it will lead to uneven airflow distribution, excessively high local wind speeds, creating “bottleneck” areas and increasing overall resistance.
3. Air flow and wind speed
Air volume: Resistance is positively correlated with the air flow (or wind speed) passing through the filter, and usually follows the “square law” – when the wind speed doubles, the resistance approximately increases to four times its original value. For instance, at the designed air volume, the initial resistance of a certain filter is 50Pa. If the actual air volume exceeds the design value by 30%, the resistance may rise to 70-80Pa.
Air flow distribution: If the filter is not installed properly (such as the frame not being sealed tightly or the clearance with the air duct being too large), it will cause air flow short circuit or local excessively high wind speed, destroying uniformity and thereby increasing resistance.
4. Dust holding capacity and service life
During the operation of the filter, dust gradually accumulates on the surface of the filter material, blocking the pores and reducing the effective channels for air flow to pass through. As the dust holding capacity increases, the resistance rises. When the resistance reaches the “final resistance” (usually 2 to 3 times the initial resistance), the filter needs to be replaced. For instance, the initial resistance of the primary filter is approximately 30 to 50Pa, and the final resistance may reach 100 to 150Pa. The initial resistance of the high-efficiency filter is approximately 150-250Pa, and the final resistance can reach 300-400Pa.
5. Physical properties of air
Temperature and humidity: High temperatures will reduce the viscosity of the air and slightly decrease the resistance. In a high-humidity environment, if the filter material absorbs moisture (such as paper filter materials), it may cause the fibers to expand, the pores to contract, the resistance to increase, and even the filter material to deform and block the air flow channel.
The nature of pollutants: The particle size, density and viscosity of pollutants in the air will affect the dust holding speed. For instance, highly viscous cooking fumes and dust tend to adhere to the surface of the filter material, accelerating pore clogging and causing the resistance to rise more rapidly. However, large particles of dust may form “Bridges” on the surface of the filter material, which instead delays the growth of resistance (but reduces the filtration efficiency).
6. Outer frame and protective net design
The sealing performance of the outer frame, the material of the protective net and the hole diameter will indirectly affect the resistance. For instance, if the protective net is made of overly dense metal mesh, it will increase the air flow resistance additionally. The connection between the outer frame and the filter material is not tight, causing turbulence in the airflow at the gaps, which may also increase the overall resistance.
Summary
The resistance of the folded frame combined filter is the result of the combined effect of multiple factors such as the characteristics of the filter material, structural design, and operating conditions. In practical applications, it is necessary to select appropriate filter materials and specifications based on the design air volume and cleanliness requirements, and ensure that the system operates under low resistance and high efficiency by regularly replacing the filters (judged based on the final resistance).
