What issues should be noted in the practical application of combined air filters?

In practical applications, combined air filters need to take into account multiple factors such as filtration efficiency, energy consumption, and maintenance. The following are the key issues to be noted and their solutions in actual use:
I. Key Points for Installation and Selection
1. Match the filter level according to the scene
Industrial cleanrooms: It is necessary to confirm whether the high-efficiency section is HEPA (filtration efficiency for particles ≥0.3μm ≥99.97%) or ULPA (filtration efficiency for particles ≥0.12μm ≥99.999%). For example, semiconductor workshops require ISO Class 5 (Class 100) standards and should be equipped with W-type non-woven high-efficiency filters.
For commercial buildings, the medium efficiency section (F7-F9) + primary efficiency section (G3-G4) can meet the daily purification requirements. If it is necessary to deal with smog, a sub-high efficiency section (F9-H10) can be added.
Medical scenarios: Operating rooms require high-efficiency sections and antibacterial coatings. In some scenarios, an additional activated carbon layer needs to be configured to adsorb odors or formaldehyde.
2. Installation sealing performance and airflow direction
Frame sealing: During installation, the gap between the filter and the frame should be filled with sealant to prevent bypass of unfiltered air (for example, the frame of a high-efficiency filter should be sealed with silicone sealant).
Airflow direction marking: Primary/medium efficiency filters are usually marked with an arrow indicating "airflow direction", while high-efficiency filters need to be installed in the correct orientation of the V-shaped/W-shaped structure (such as the open end of the filter element facing the airflow), otherwise the filtration efficiency will be reduced.
Ii. Operation and Maintenance Management
Resistance monitoring and replacement cycle
Resistance threshold
Primary filter: Replace when the initial resistance is ≤50Pa and the final resistance is 100-150Pa.
Medium-efficiency filter: Replace when the initial resistance is ≤80Pa and the final resistance is 150-250Pa.
High-efficiency filters: Replace when the initial resistance is ≤250Pa and the final resistance is 400-600Pa (or the service life is ≥1.5 years).
Monitoring method: A differential pressure gauge can be installed for real-time monitoring, or the resistance alarm value can be set through the PLC program of the air conditioning system to avoid a decrease in air volume due to excessive resistance (such as a 10%-20% increase in fan energy consumption).
2. Dust holding capacity and cleaning limitations
Primary/medium efficiency washable types:
The plate-type primary filter (G3-G4) can be rinsed with clean water or blown back with compressed air, but the cleaning frequency should be no more than 5 times; otherwise, the filter material fibers will break, reducing the efficiency.
Bag-type medium efficiency (F7-F8) is not recommended for cleaning. It should be replaced directly to avoid deformation of the filter bag and air leakage after cleaning.
High-efficiency filters must not be cleaned: Their filter materials are made of glass fiber or composite fiber. Cleaning will damage the pleated structure, causing a sudden drop in filtration efficiency. They must be replaced as a whole.
III. Environmental Adaptation and Special Scenario Response
1. The influence of temperature, humidity, and corrosive gases
High-temperature resistant scenarios, such as spray painting workshops (temperature ≤80℃), high-temperature resistant and high-efficiency filters (frame made of stainless steel, sealant made of silicone rubber) should be selected. Ordinary filters may experience filter material deformation or rubber strip aging and air leakage at high temperatures.
High humidity environment: For pharmaceutical workshops (humidity ≥60% RH), waterproof filters (with coating on the filter material and frames made of aluminum alloy or ABS plastic) should be selected to prevent mold on the filter material or rust on the metal frame.
Chemical pollution scenario: The etching process in an electronics factory may produce acidic gases. It is necessary to add a chemical filter (activated carbon layer) after the combined filter to prevent the filter material of the high-efficiency filter from being corroded.
2. Filtration requirements for special pollutants
Oil mist/fume environment: A metal mesh oil mist filter should be added before the primary efficiency section of the kitchen exhaust unit to prevent grease from clogging the medium/high-efficiency filter materials (grease adhesion will cause a sharp increase in resistance and shorten the replacement cycle).
Microbial control: The filters in hospital operating rooms need to be disinfected with ozone or ultraviolet light regularly (every quarter) to inhibit the growth of bacteria on the surface of the filter materials and prevent secondary pollution.
Iv. Optimization of Energy Consumption and System Matching
1. The power of the fan is balanced with the filtration resistance
The total resistance of the combined filter should be controlled within 70% to 80% of the designed air pressure of the fan (if the total resistance exceeds 500Pa, a high-power fan should be replaced), otherwise it will lead to insufficient air volume (such as the air change rate in the clean room not meeting the standard).
Variable frequency fans can be used to automatically adjust the rotational speed according to the resistance of the filter. For instance, when the final resistance of the high-efficiency filter reaches 400Pa, the fan speed can be increased by 15% to maintain a stable air volume and reduce energy waste.
2. Modular design and space adaptation
For the combined filters in large air conditioning units, a maintenance passage (width ≥600mm) should be reserved to facilitate the replacement of filter elements. If space is limited, foldable medium-efficiency bags (such as F9 grade M-type bag filters) can be selected to reduce the installation depth.
V. Safety and Compliance Requirements
1. Special specifications for medical/industrial scenarios
Pharmaceutical industry: GMP standards must be met. After the high-efficiency filter is replaced, a PAO leak test should be conducted (the leakage rate detected by a photometer should be ≤0.01%) to ensure there are no filtration blind spots.
Biosafety laboratories: For level 3/4 laboratories, the exhaust filters should be equipped with double-stage high-efficiency filtration, and the exhaust ducts should be fitted with disinfection devices (such as ultraviolet lamps) to prevent the leakage of pathogenic microorganisms.
2. Disposal of waste filters
Waste filters from ordinary industrial/commercial scenarios can be treated as general solid waste. Filters in medical Settings (such as infectious disease wards) must first undergo high-temperature sterilization (≥121℃ for 30 minutes) or chemical disinfection, and then be incinerated as medical waste to prevent the spread of microorganisms.
Summary
The practical application of combined air filters requires full-process control from "selection - installation - maintenance - environmental adaptation". The core lies in ensuring the balance between filtration efficiency and system energy consumption through resistance monitoring, regular replacement, and targeted anti-corrosion/antibacterial design, while also complying with industry standards (such as GMP, ISO 14644). Avoid air quality not meeting standards or equipment failure due to improper maintenance.