How to reasonably determine the air filters at all levels?
Generally, the last level of air filter determines the cleanliness of the air supply, and 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 shall be determined according to the cleanliness requirements of the air supply, and then the air filter (pre-filter) for protection shall be selected. If this air filter also needs to be protected, the filter shall be added at its upper air end. The efficiency of air filters at all levels shall be properly matched. If the efficiency difference between the two adjacent levels is too large, the former level will not protect the latter level.
When using the European "G ～ F ～ H ～ U" efficiency specification classification, the 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.
The selection of pre-air filter shall be determined after comprehensive consideration of such factors as operating environment, spare parts cost, operation energy consumption, maintenance and supply. In particular, the HEPA air filter at the end of the clean room should be protected by an efficiency specification no less than F8 medium efficiency filter; The air filter from F9 medium efficiency filter to H11 can be selected before the very high efficiency (ULPA) air filter. The air conditioning system itself shall be protected by a medium efficiency filter with an efficiency specification not lower than F5. In areas without wind, sand and low pollution, no pre-filter can be set in front of F7 medium efficiency filter; In urban air conditioning systems, the common primary efficiency filters are G3~F6.
The key points to determine the efficiency of the air filter are: the performance of the final air filter should be reliable, the efficiency specification of the pre-filter should be reasonable, and the maintenance of the primary filter and pre-filter should be convenient.