How to reasonably determine each level of air filter?
Generally, the last level of air filter determines the cleanliness of the supply air, while the upstream level of air filter plays a protective role. It protects the lower air filter to extend its service life, or protects the air conditioning system to ensure its normal operation.
During design, the efficiency of the final air filter should be determined first based on the cleanliness requirements of the air supply, and then the air filter (pre filter) that serves as a protection function should be selected. If this level of air filter also needs protection, then a filter should be added at its upstream end. The efficiency of each level of air filter should be properly matched. If the efficiency difference between adjacent two levels is too large, the former level will not directly protect the latter level.
When using the European "G ～ F ～ H ～ U" efficiency specification classification, a primary filter can be set every 2-4 gears. For example, G3 → F5 → F8 → H12, where the terminal H12 high-efficiency filter determines the cleanliness level of the air supply, F8 protects H12, F5 protects F8, and G3 protects F5.
When selecting a pre air filter, it is necessary to comprehensively consider factors such as the operating environment, spare parts costs, operating energy consumption, maintenance, and supply before deciding. In particular, the clean room end high efficiency (HEPA) air filter should be protected by a medium efficiency filter with an efficiency specification no lower than F8; Before very high efficiency (ULPA) air filters, F9 medium efficiency filters to H11 air filters can be selected. The air conditioning system itself should be protected by a medium efficiency filter with an efficiency specification not lower than F5. In areas without wind, sand, and low pollution, pre filters may not be installed before F7 medium efficiency filters; In urban air conditioning systems, the current common primary efficiency filters are G3 to F6.
The key points for determining the efficiency of an air filter are: the performance of the final air filter should be reliable, the efficiency specifications of the pre filter should be reasonable, and the maintenance of the primary and pre filters should be convenient.