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Filter Testing

The performance of an air filter is generally evaluated based on four parameters. These include:

Contaminant removal efficiency
Contaminant holding capacity
Resistance to airflow
Safety with regard to support or spread of fire and smoke
Contaminant removal efficiency is tested by challenging the filter with contaminant on the upstream side and measuring the residual contaminant on the downstream side of the filter after the air has passed through the media. Various methods and instruments have been developed for moving the air through the filter, holding the filter, generating and dispursing the challenge, and measuring the challenge on the upstream and downstream side of the filter.

Contaminant holding capacity is determined by measuring the mass of contaminant removed before the filter reaches its maximum differential pressure in the case of particle filters or before the contaminant breaks through the filter in the case of a gaseous filter.

Resistance to airflow is determined by measuring the pressure of the air upstream of the filter and downstream of the filter and comparing those values. The value of resistance to airflow must be accompanied by the value of airflow velocity in order to truly understand the performance of the filter.

Safety in a situation where a filter is exposed to flame is measured by its support of fire when no other fuel source is present (the filter is therefore a fuel source), the amount of smoke generated by the filter, and the release of sparks by the filter when exposed to the heat of a flame.

Life Cycle Cost (LCC)

From a long term perspective, it is evident that the energy consumption is the major overall cost of a filter

70 % of the cost is energy!

Calculations reveal that energy normally accounts for 70 % of the total LCC of the system. The energy consumption is directly proportional to the average pressure drop over the life of the filter.

Choosing the right filter saves energy

Many people assume that the filter efficiency is the largest contributor to initial pressure drop, however, it is the actual design of the filter that has the main impact!

Air Filter Testing
Nothing is ever black and white. A 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 the performance of an air filter changes over time. The challenge imposed on air filters changes as the environment inside and outside of a building changes. Many air filter testing methods have been developed by various organizations for predicting the in-use performance of filters and for comparing the performance of air filters of different designs.

It is important to understand the complexity of differentiating air filters. Many variables impact the results of a comparison study, some of which are obvious and some of which aren't. Most air filters will be 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, airflow velocity, and particle load. However, testing of filters often occurs in a controlled environment. Add to this the imperfect design of testing methods and the various motivations of the people developing test methods and you can conclude 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 an area of focus but their standards and testing methods may overlap in some cases.




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