1 Introduction to Dust Holding Capacity in Various National Standards
According to JG/T 22-1999, dust holding capacity is defined as the total artificial dust captured by the tested filter before reaching the test termination condition, calculated by multiplying total injected artificial dust mass by the average weight efficiency of the tested filter.
The test procedure is as follows: artificial dust is delivered into the standard test duct equipped with the tested filter and final high-efficiency filter. After dust feeding, both filters are removed and weighed to calculate mass difference and weight efficiency. The process is repeated until the tested filter reaches final pressure drop. The average weight efficiency throughout the test is multiplied by total dust supply to obtain the dust holding capacity.
The definition and test method of dust holding capacity in EN 779:2002 are almost identical to JG/T 22-1999. ANSI/ASHRAE 52.1-1992 is consistent with JG/T 22-1999 except for test termination conditions. JIS B 9908:2001 is roughly the same as JG/T 22-1999 except different termination rules and calculation formulas.Therefore, differences among standards mainly lie in test termination conditions and dust capacity calculation methods, as summarized in Table 1.
2 Test Termination Conditions of Dust Holding Capacity
As shown in Table 1, all four standards take final pressure drop as the termination criterion. JG/T 22-1999 and EN 779:2002 adopt only this criterion, while ANSI/ASHRAE 52.1-1992 and JIS B 9908:2001 also use weight efficiency degradation to judge test completion.
2.1 Final Pressure Drop as Termination Condition
Pressure drop of most filters keeps rising continuously. Thus final pressure drop can directly determine test end. Dust holding capacity is highly correlated with final pressure drop: higher set final pressure drop leads to larger measured dust holding value.
There are two common ways to define final pressure drop: twice initial pressure drop, or values recommended by manufacturers.Filters with low initial pressure drop face unfair evaluation when adopting double initial pressure drop. Manufacturer-recommended values lead to inconsistent standards among products, making dust capacity incomparable and confusing customer selection.Therefore unified final pressure drop specifications should be formulated for each filter grade. Recommended values in Reference 2 are highly referable.
2.2 Weight Efficiency Decline as Termination Condition
For low-efficiency filters made of loose coarse fiber materials, accumulated dust will penetrate the filter layer, fall off and cause secondary dust emission, resulting in decreasing pressure drop instead of rising.In this case, efficiency reduction is required to terminate tests, as specified in clauses b & c of ANSI/ASHRAE 52.1-1992 and clause b of JIS B 9908:2001.JG/T 22-1999 and EN 779:2002 lack such provisions, so the standard needs supplementary improvement during revision.
3 Calculation Methods of Dust Holding Capacity
JG/T 22-1999, ANSI/ASHRAE 52.1-1992 and EN 779:2002 share the same formula: dust holding capacity = total dust mass × average weight efficiency.JIS B 9908:2001 calculates dust capacity directly by weighing mass change of tested filters or terminal filters.
The former method relies on average weight efficiency, which is only applicable to coarse filters and meaningless for medium and high-efficiency filters.By contrast, JIS B 9908:2001 calculation is simpler, more intuitive and accurate. It is recommended to adopt direct weight difference method when revising JG/T 22-1999.
4 Conclusion
- JG/T 22-1999 has ambiguous regulations on final pressure drop and incomplete termination criteria, which shall be optimized in standard revision.
- The dust holding calculation method of JIS B 9908:2001 is concise and intuitive, worthy of reference for JG/T 22-1999 revision.
- Dust holding capacity is a vital performance indicator of air filters. Its test procedures shall be improved during standard updating to achieve simple, standardized and reliable operation.