Nothing is ever black and white. The perfect air filter would operate at 100% efficiency on the target contaminants, require zero energy input, and last forever. However, no filter of this type has been invented.
Filter efficiency, dust holding capacity and differential pressure can be measured in many ways, and an air filter's performance changes over time. The challenge imposed on air filters changes as the environment inside and outside a building changes. Many air filter testing methods have been developed by various organizations for predicting the in-use performance of filters and comparing the performance of air filters of different designs.
It is important to understand the complexity of differentiating air filters. Many variables impact on the results of a comparison study, some of which are obvious and some of which aren't. Most air filters will remain in a system for months or even years. However, testing of these filters often occurs in a few minutes or hours. During its life, an air filter will see dozens or hundreds of environmental changes such as temperature, humidity, air flow velocity and particle load. However, filters are often tested in a controlled environment. Add to this the imperfect design of testing methods and the various motivations of the people developing test methods, and it becomes clear that you must fully understand how to interpret the results of any air filter test you are presented with prior to using these results to make important decisions.
Organizations involved in setting filter standards and testing methods include:
- American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE)
- Institute of Environmental Sciences and Technology (IEST)
- Underwriters Laboratories (UL)
- International Organization for Standardization (ISO).
Each of these organizations has a specific focus area, but their standards and testing methods may overlap in some cases.
Camfil has developed several additional methods for predicting in-use performance, determining the performance of air filters in use (in situ), and comparing the performance of air filters of different designs.
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