Key Points in the Selection and Design of Filters for Ventilation and Air Conditioning Systems

June 19, 2024

In ventilation and air conditioning systems, filters are a critical component whose performance directly affects indoor air quality, system operating efficiency, and maintenance costs. Therefore, the reasonable selection and design of filters are crucial to ensuring the normal operation of the ventilation and air conditioning system and the comfort of the indoor environment. The following are the main points for the selection and design of filters in ventilation and air conditioning systems.

1. Selection Guide for Coarse Filters (G1~G4)

- Applications: Suitable for places with particle sizes > 5μm to remove dust, pollen, mites, sand, paint spray, fiber dust, catkins, etc.; used as pre-filters for F-grade filtration, the minimum filtration requirement for ventilation and air conditioning systems, low-demand public buildings, residential buildings, to protect the air conditioning system, and as pre-filters for chemical filters.

- Common Types: Inexpensive washable bag filters, disposable panel filters, automatic winding filters, and electrostatic filters.

 2. Selection Guide for Medium and High-Efficiency Filters (M5~M6, F7~F9)

- Applications: Suitable for places with particle sizes 0.1~10μm to remove most microorganisms, most dust, welding smoke, and pollen; for high-demand public buildings, residential buildings, workshops, wards, clinics, pre-filtration for HEPA (usually F8), to protect air conditioning systems, intake air filtration for paint shop sheds, gas turbines, and air compressors (usually F7), and pre-filters for chemical filters.

- Common Types: Bag filters, W-type separatorless filters, high-temperature separator filters, separator filters, self-cleaning filters, and electrostatic filters.

- Notes: For comfort air conditioning, particulate air filters can have pre-filters and main filters. The main filter determines the cleanliness of the supply air, while the pre-filter protects the main filter. Typically, coarse or medium efficiency filters are used as pre-filters and medium or high-efficiency filters as main filters.

3. Particulate Air Filters

- Types: Panel and bag filters can be used as coarse and medium filters; electrostatic filters can be used as medium and high-efficiency main filters in ventilation and air conditioning systems, with coarse filters upstream for protection.

4. Gaseous Pollutant Air Filters

- Types: Photocatalytic filters, activated carbon filters, high-voltage electrostatic filters.

- Applications: Photocatalytic filters can decompose gaseous pollutants such as formaldehyde, benzene, ammonia, and hydrogen sulfide into CO2 and H2O, and kill bacteria, viruses, and mold in the air. Activated carbon filters can adsorb gases with large molecular weights, high boiling points, and volatile organic compounds. Chemically treated activated carbon can adsorb specific pollutants such as formaldehyde, sulfur dioxide, ammonia, and nitrogen oxides. To extend the life of activated carbon, medium or higher-efficiency filters should be installed upstream. High-voltage electrostatic filters are less effective at removing organic gas pollutants.

5. Microbial Air Filters

- Types: Photocatalytic filters decompose gaseous pollutants and kill microorganisms by producing hydroxyl radicals. High-voltage electrostatic filters can remove certain bacteria.

6. Engineering Design Points

1. Comfort Air Conditioning: If coarse filters do not meet indoor air quality requirements, medium filters should be added.

2. Process Air Conditioning: Filters should be set according to the cleanliness requirements of the air conditioning zone.

3. Air Filter Resistance: This should be calculated based on final resistance.

4. Filter Placement: This should be inside the air handling unit; if placed in ducts, the air velocity should meet filter technical requirements and allow for replacement.

5. Civil Buildings: Comfort air conditioning systems generally use coarse or a combination of coarse and medium filters.

6. All-Air Systems: Filters must meet the needs of full fresh air operation during transitional seasons.

7. High Density or High Air Quality Areas: Full air systems should have purification devices to ensure indoor air quality. The type of purification device should be determined based on personnel density, initial investment, operating costs, and environmental requirements, with technical and economic comparisons. The type of purification device should match the nature of the pollutants and meet relevant standards.

In summary, the selection and design of filters for ventilation and air conditioning systems need to consider multiple factors. By comprehensively considering these factors, the selected filters can meet the actual needs of the system, improve indoor air quality, reduce system energy consumption and maintenance costs, and create a more comfortable and healthy environment for people's lives and work.