If you want to choose the most important one during the operation of a high-efficiency air filter from numerous technical parameters, the answer is usually resistance, or more accurately, the dynamic changes in initial and final resistance. Although the filtration efficiency determines whether it can meet the standard, resistance is a direct reflection of whether it can work normally in the actual system, how much energy it consumes, and when maintenance is needed. Their relationship can be understood as follows:
Filtering efficiency is a qualification indicator - it determines whether it can be used or not.
Resistance is an operational indicator - it determines whether it is used well and how long it can last.
In practical engineering and operational management, the following parameters together constitute the "core parameter group" for evaluating its operational status:
1. Core King: Resistance (pressure difference), resistance is the most intuitive parameter that reflects the state of the filter itself and its compatibility with the air conditioning system.
Initial resistance:
- Definition: The initial resistance of a filter at rated airflow.
- Importance: It determines the basic pressure head that the fan needs to provide. The lower the initial resistance, the more reasonable the design of the internal airflow channel of the filter, the better the permeability of the filter material, and the lower the operating energy consumption.
Final resistance:
- Definition: The recommended value is usually twice the initial resistance, or when the resistance reaches a certain set threshold (such as 400-600Pa).
- Importance: It is the main basis for determining whether the filter needs to be replaced. When the resistance exceeds the design value, the air volume of the air conditioning system will significantly decrease, resulting in insufficient air exchange in the clean room and thus damaging the cleanliness.
Resistance change rate:
Importance: Observing the growth rate of resistance can determine the utilization of dust holding capacity. The gently rising resistance curve represents deep filtration with a long lifespan; The steep upward curve represents surface blockage and short lifespan.
2. Efficiency and leakage rate: The bottom line of safety assurance, these two parameters are the red line to ensure that the cleanroom level does not fail.
Most easily penetrated particle size efficiency:
- Definition: The filtration efficiency of a filter for the most difficult 0.1-0.3 μ m particles to filter.
- Importance: This is the core performance indicator of the filter. Only by ensuring MPPS efficiency can the filtration effect be guaranteed for all particle sizes in the air. If the efficiency of MPPS decreases, the cleanliness of the cleanroom cannot be guaranteed.
Scan leakage rate:
- Definition: When conducting a comprehensive scan of the filter with aerosols, the local penetration rate shall not exceed 0.01%.
- Importance: The most common failure mode of filters is leakage, not blockage. A leakage point the size of a needle tip can cause the local cleanliness to instantly return to zero. Therefore, the leakage rate is the key to determining whether the filter is qualified.
3. Wind speed and airflow uniformity: comfort and self-cleaning ability
Surface wind speed:
- Definition: The velocity of airflow through the entire cross-section of a filter.
- Importance: High wind speed, significant increase in resistance, and possible generation of secondary dust; If the wind speed is too low, it cannot meet the requirements for air exchange rate in the clean room. The typical design wind speed is 0.45 m/s ± 20% (for laminar flow hoods) or determined based on air volume calculations.
Wind speed uniformity:
- Definition: The consistency of wind speed at each point on the entire outlet surface of the filter.
- Importance: For unidirectional flow cleanrooms, uniformity is crucial. Uneven airflow can generate eddies and blind spots, making it difficult to effectively remove pollutants. Usually, a relative standard deviation of less than 20% is required.
4. Dust holding capacity: an economic indicator of lifespan
- Definition: The total amount of dust that the filter can intercept before reaching the final resistance.
- Importance: It directly determines the replacement cycle of the filter. The larger the dust holding capacity, the longer the service life, and the lower the downtime loss and procurement cost caused by replacement. This is an important parameter for measuring the cost-effectiveness of filters.
summary
In the operation and management of high-efficiency air filters, these parameters each have their own focus:
Resistance is the focus of daily monitoring, used to determine when filters need to be replaced.
Efficiency/leakage rate is a key focus of regular verification to confirm whether the filter can still maintain the cleanliness bottom line.
Wind speed/dust holding capacity is a reference for selection, debugging, and economic evaluation.
Therefore, when reviewing the operation report of a high-efficiency filter, it is recommended to prioritize whether the resistance value is within the normal range and whether the recent high-efficiency leak detection has passed. These two points can basically determine whether the current operating status of the filter is healthy.