Reasonable determination of filter efficiency at all levels
In general, the last stage filter determines the air cleanliness, and the upstream filter only plays a protective role. It protects the downstream filter to prolong its service life, or protect the air conditioning system to ensure its normal operation.
In the design of air conditioners, the efficiency of the last stage filter should be determined first according to the user’s cleanliness requirements, and then the filter that plays a protective role should be selected. The protective filters are collectively referred to as “pre-filters”.
The efficiency of the filters at all levels should be properly matched. If the gap between the efficiency specifications of the adjacent two-stage filters is too large, the former stage cannot protect the latter stage; if the difference is not large, the burden of the latter stage is too small.
The service life of the high-efficiency filter at the end of the clean room should be 5 to 15 years. The main factor affecting the service life is the quality of the pre-filter.
When using the “G~F~H~U” efficiency specification classification, it is convenient to estimate the efficiency of the required filter stages. In G2～H12, set the primary filter every 2～4 steps.
For example: G4→F7→H10, where the end H10 (sub-high efficiency) filter determines the cleanliness level of the supply air, F7 protects H10, and G4 protects F7.
Before the high efficiency (HEPA) filter at the end of the clean room, a filter with an efficiency specification not lower than F8 should be used for protection; before the very high efficiency (ULPA) filter, a filter of F9~H11 can be selected. The central air conditioner itself should be protected by a filter whose efficiency specification is not lower than F5.
In areas with no sandstorm and low pollution, there is no need to set a pre-filter in front of the F7 filter; in the central air-conditioning system of the city, G3~F6 are common primary filters.
What kind of pre-filter should be installed to protect the latter-stage filter, which requires designers and field engineers to decide after comprehensive consideration of factors such as the use environment, spare parts costs, operating energy consumption, and maintenance costs.
● In a class 100 clean room, F5→F8→H10→H13 four-stage filtration is set up, and the H13 filter at the end has been used for 8 years.
● There is only F5 filter in front of the high-efficiency filter in a clean room, and the user needs to replace the high-efficiency filter every year.
● The filter in a fresh air purification system in a heavily polluted city is set to G3→H10, and the H10 filter will be scrapped after the system runs for half a month.
● In an automobile painting line, the filter is set to G3→F6→F5. Among them, the end F5 is the filter material covered on the roof, which only plays the role of equalizing the flow required by the process;
F6 determines the purification level of the supply air.
The performance of the final filter should be reliable.
The efficiency specification of the pre-filter should be reasonable.
The maintenance of the primary filter should be convenient.
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