In the field of air quality control, scientifically evaluating the true effectiveness of filters has long been a challenge. Traditional testing methods are often based on single-point efficiency at specific particle sizes, lacking a direct correlation with the health hazards of particulate matter and failing to predict actual performance in use. The release of the ISO 16890 series of standards marks the entry of air filter evaluation into an era of health-related testing. Pressure system testing, as a core testing method, not only establishes a standardized laboratory evaluation procedure but, more importantly, scientifically links filtration efficiency to the health effects of particulate matter, providing a reliable basis for filter selection in different application scenarios.
01 Testing Principles: From Aerosol Generation to Efficiency Calculation
Pressure system testing begins with the preparation of polydisperse test aerosols. The standard recommends using DEHS (diethylhexyl sebacate) or KCl (potassium chloride) solutions, generating particles with a size range of 0.3-10 micrometers using a precision atomizer. These substances are chosen for their physicochemical stability and optical detection characteristics, ensuring the repeatability of the test.
The generated particles then enter an electrostatic neutralizer to eliminate the charge carried by the particles, simulating the state of suspended particles in the real atmosphere after thorough mixing, which is close to electrically neutral. This step is crucial because it eliminates the influence of electrostatic effects on filtration efficiency, separately evaluating the mechanical capture ability of the filter medium.
In the test duct, the filter is installed in a standard-sized (610mm × 610mm) test section, with isokinetic sampling probes upstream and downstream. These probes draw air samples at precisely controlled flow rates and send them to an optical particle counter for analysis. The efficiency for each particle size channel (typically including 0.3, 0.5, 1.0, 2.5, 5.0, and 10.0 micrometers) is calculated from the upstream and downstream concentration ratio.
For charged filter materials (such as most melt-blown electret materials), the testing procedure is more rigorous. In addition to initial efficiency, “IPA treatment” is required—exposing the filter to isopropanol vapor to eliminate its electrostatic adsorption capacity, and then retesting. This treatment simulates the worst-case scenario of gradual electrostatic decay during filter use, and the final reported value is a weighted average of the initial efficiency and the efficiency after IPA treatment.
02 Engineering Significance of Airflow Resistance Measurement
In pressure system testing, airflow resistance (pressure drop) measurement is by no means a secondary parameter. Resistance directly affects the energy consumption and operating costs of the ventilation system. Tests are conducted at different airflow rates (50%, 75%, 100%, and 125% of the rated airflow) to plot a complete resistance curve. The initial resistance (resistance at the rated airflow) and the resistance growth characteristics together determine the energy consumption performance of the filter.
Resistance testing uses high-precision differential pressure sensors (typically with an accuracy of ±0.5 Pa) to measure the static pressure difference at specific locations before and after the filter (standard specified distance of 150 mm from the filter surface). This measurement location is carefully designed to avoid airflow disturbances affecting measurement accuracy.
In practical engineering applications, resistance data combined with efficiency data can be used to calculate the filter’s energy efficiency index, which is an important parameter for evaluating the overall performance of the filter. The quality factor (QF) is defined as the product of the logarithm of the efficiency and the reciprocal of the resistance, comprehensively reflecting the performance efficiency of the filter. This indicator provides a quantitative basis for filter selection in different application scenarios, helping to balance filtration effectiveness and operating costs. For example, in commercial building HVAC systems, an ePM 1 70 filter may have 30-50% lower resistance than an ePM1 80 filter, meaning that fan energy consumption can be reduced by 15-25% accordingly. For buildings operating year-round, this represents considerable energy-saving potential.
03 Scientific Basis of Particle Size Classification and Health Associations
The most significant advancement of ISO 16890 is the direct correlation of filter performance with health effects. The standard classifies PM1, PM2.5, and PM10 based on filtration efficiency, supported by conclusive evidence from epidemiological studies:
PM10 (≤10 micrometers): Primarily deposited in the upper respiratory tract; long-term exposure is associated with chronic bronchitis and pharyngitis;
PM2.5 (≤2.5 micrometers): Can penetrate deep into the alveolar region and is closely associated with increased risk of cardiovascular disease and lung cancer;
PM1 (≤1 micrometer): Can penetrate the alveolar wall and enter the bloodstream, associated with systemic inflammatory responses and neurological diseases.
The test uses particles in the 0.3-10 micrometer range, but the classification is determined by weighted calculations of filtration efficiency for PM1, PM2.5, and PM10. This method considers the distribution characteristics of particles of different sizes in actual air, making the laboratory test results closer to performance in real-world environments.
04 Practical Applications and Challenges of Standard Implementation
The results of the pressure system test directly affect the selection and application of filters:
In medical environments, operating rooms and intensive care units typically require filters with ePM1 80 or higher. These filters have a retention efficiency of over 99% for bacteria and viruses, and when combined with appropriate air exchange rates, can effectively control the risk of hospital-acquired infections. The air handling system at Charité Hospital in Berlin, Germany, uses such high-grade filters to ensure air quality in high-risk areas.
In industrial applications, professional companies such as Trenntech customize solutions for different industries based on test results. For example, in the pharmaceutical industry, cleanrooms require stable particle control, demanding filters that not only have high initial efficiency but also exhibit slow efficiency degradation after dust loading; while in paint shops, filters need to focus on the adsorption capacity of specific chemical components, requiring standard testing to be supplemented with chemical filtration efficiency assessment.
However, the implementation of ISO 16890 also faces challenges. The investment in testing equipment is substantial; the cost of high-precision particle counters and standard test ducts alone can exceed one million RMB, limiting the testing capabilities of small and medium-sized manufacturers. Furthermore, there are still differences between standard testing and actual usage environments—real air contains a complex composition of particles (including oily, solid, and biological particles), while the test mainly uses liquid DEHS or solid KCl particles, which may lead to deviations in performance evaluation.
05 Technological Frontiers and Standard Development
With the development of air purification technology, the ISO 16890 standard is also constantly evolving. Future revisions may consider:
1. Real-world air testing methods: Supplementing performance evaluation with actual air samples to better simulate the usage environment;
2. Ultrafine particulate matter assessment: Adding efficiency assessment for the 0.1-0.3 micrometer particle size range, as particles in this size range have high number concentrations and significant health impacts;
3. Chemical filtration integration: Combining the assessment of gas pollutant removal efficiency to provide more comprehensive air purification performance indicators;
4. Smart filter assessment: Developing corresponding testing protocols for new types of filters that are monitorable and adjustable.
These developments will make pressure system testing more comprehensive and better serve the needs of indoor air quality control.
The performance evaluation of air filters has evolved from simple “efficiency percentages” to a scientific classification system based on health effects, reflecting the deep integration of technological progress and health protection. The ISO 16890 pressure system test, as a core method of this system, not only ensures the scientific validity and comparability of test results but also promotes continuous innovation in filtration technology, providing a solid foundation for improving indoor air quality worldwide.