The efficiency, resistance, air volume, and wind speed of an air filter are the core technical parameters that determine its performance. These four parameters are interrelated and together determine whether the filter is suitable for a specific scenario and its long-term economic viability.
1, Definition and Relationship of Four Core Parameters
- 1. Efficiency: The ability of a filter to capture pollutants. Efficiency (%)=(1- downstream concentration/upstream concentration) × 100%; Grading criteria: G1-H14 (based on EN 1822/ISO 16890) Efficiency is the core functional indicator that determines the cleanliness level.
- 2. Resistance: The obstruction that air experiences when passing through a filter. Unit Pa (Pascal); Initial resistance: resistance of the new filter; Final resistance: The resistance required for replacement (usually 2-3 times the initial resistance), which is the core energy consumption indicator and directly affects the energy consumption and operating costs of the fan.
- 3. Airflow: The volume of air that passes through a filter per unit of time. Unit: m ³/h (cubic meter/hour) or CFM air volume is the processing capacity indicator, which determines the applicable space size.
- 4. Wind speed: The speed at which air passes through the surface of the filter material. Unit: m/s (meters/second), face wind speed=air volume/filter windward area, wind speed is a regulating valve for efficiency and resistance. If it is too high, it will reduce efficiency and increase resistance.
2, The core logical chain of the four major parameters
These four parameters do not exist in isolation, they follow the following internal logic:
- 1. The air volume and wind speed determine the size of the filter:
After the required air volume is determined, wind speed becomes the key factor in the design. To pursue low drag, it is usually desirable to have lower wind speeds. Therefore, engineers will design the filter size by reducing the wind speed (i.e. increasing the filtration area).
Formula: Filter area=air volume/surface air velocity
- 2. Wind speed and filter material jointly determine resistance and efficiency:
The higher the wind speed, the greater the impact force of the air on the filter fibers, and the resistance increases in a square order.
The higher the wind speed, the particles may not have enough time to be captured by the fibers due to their high inertia, and may be "knocked away" or "blown away", resulting in a decrease in efficiency. Especially for high-efficiency filters, wind speed is a key variable.
The denser the filter material, the stronger its interception ability (higher efficiency), but the more difficult it is for air to pass through (greater resistance).
- 3. The dust holding capacity and resistance determine the service life:
As the amount of dust intercepted by the filter increases, the gaps between the filter fibers become blocked, and the resistance gradually increases. When the resistance reaches the set final resistance, even if the filter is not completely blocked, it means that its economic service life has reached the end and needs to be replaced.
3, Common scenarios and interpretations in engineering applications
- 1.The "seesaw effect" between parameters, in practical applications, these four parameters often need to be balanced.
Case: The nominal parameters of a filter are air volume of 2000 m ³/h, initial resistance of 150 Pa, and efficiency F9.
If the actual operating air volume increases to 2500 m ³/h, the resistance will sharply increase (possibly exceeding 250 Pa) as the wind speed rises. Efficiency may slightly decrease due to increased particle penetration at high wind speeds.
Inspiration: When choosing a filter, it is not enough to only consider individual parameters, but must be matched based on the efficiency and resistance under the designed air volume.
- 2. Trap of rated air volume: Many users easily overlook that the nominal resistance and efficiency of the filter are measured at the rated air volume.
If a household filter with a rated air volume of 1000 m ³/h is forcibly used on a fresh air fan that requires 2000 m ³/h, it will result in excessive wind speed, soaring resistance, insufficient system air volume, and greatly reduced purification efficiency.
Suggestion: It is best to control the actual operating air volume within the range of 80% -120% of the rated air volume.
- 3. Guiding significance of surface wind speed: Surface wind speed is an important indicator for measuring the rationality of filter selection.
Coarse efficiency filter: The surface wind speed is usually between 1.0-2.5 m/s.
High efficiency filter (HEPA): The surface air velocity is usually between 0.3-0.5 m/s.
If the surface wind speed of your high-efficiency filter exceeds 0.8 m/s, it indicates that the filtration area may be insufficient, which can lead to high resistance and shortened lifespan.
4, Summary: How to comprehensively use these four parameters for selection?
When faced with a filter technical parameter table, it is recommended to evaluate it in the following order:
- 1. First, check the efficiency: confirm whether the level meets your cleaning needs (e.g. F7-F9 for household use and H13-H14 for medical use).
- 2. Check the air volume again: Confirm whether the rated air volume of the filter matches your device.
- 3. Calculate surface wind speed: Divide the air volume by the external area of the filter to see if it is within a reasonable range.
- 4. Evaluate resistance: At rated airflow, the lower the resistance, the better the long-term energy consumption.