Indoor Air Resources

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Filter Specification: 5 Ways You're Doing it Wrong

March _Selection Tips

By: Kevin Morrow, Business Development Manager, Kimberly-Clark Professional Partnership Products  |   03.09.15

MERV ratings. Pleat quantity. Total media area. Purchase price. These variables are typically evaluated when selecting an HVAC air filter, and indeed they should be. But if you neglect other performance factors during the evaluation process, you could end up with an air filtration system that does not provide the superior air quality building occupants demand or that increases your energy costs. 

If you don’t look beyond MERV, you’re doing it wrong. Depending on the type of filter media used (mechanical-only or electret-treated), two similar filters of the same MERV rating can have different filtration efficiencies. It’s best to evaluate the full ASHRAE 52.2 test report to see the efficiency of the filter over three particle size ranges: E1 (very fine particles in the 0.3 to 1.0 micron range), E2 (fine particles in the 1.0 to 3.0 micron range), and E3 (coarse particles in the 3.0 to 10.0 micron range). 

High E1 and E2 efficiencies are critical for good IAQ and helping building occupants avoid airborne-related illness. However, many pleated filters today (especially at commonly used MERV 8) have very low E1 and E2 efficiencies. In fact, under the ASHRAE 52.2 Standard, there was no minimum requirement for E1 particulate capture below a MERV 14 and no minimum requirement for E2 particle capture below a MERV 9 until this year, meaning that MERV 8 products currently on the market are classified solely on their E3 efficiency. 

If you neglect to evaluate airflow resistance, you’re doing it wrong. Energy costs—relating to how much energy is needed to push the air through the filtration system —are the largest component of an air filtration system’s total lifetime costs (at about 81 percent). A low airflow resistance in the filter media translates into reductions in energy consumption and costs. Filters with media using only mechanical methods of air filtration tend to create significant airflow resistance, because their filtration mechanisms cause disruption of particles in the air stream. A filter’s airflow resistance can be found in its full ASHRAE 52.2 Test Report. 

If you specify a filter based only on its Appendix J test results, you’re doing it wrong. The optional MERV-A test in Appendix J of the ASHRAE 52.2 Standard subjects filters to extreme loads of fine potassium chloride particles—many times what the filter would be exposed to over its real-world, installed, useful life. In fact, a number of people within the industry don’t believe that Appendix J accurately reflects real-world conditions, but instead a worst-case scenario that is likely to never happen. 

While the optional Appendix J test method may be conducted at the filter manufacturer’s discretion, only the standard, ANSI-certified ASHRAE 52.2 test method can be used to indicate the filter’s true performance. 

If you don’t consider the benefits of electret-charged filter media, you’re doing it wrong. Electret-treated filter media can provide high initial and high sustained efficiency over the filter lifecycle. Filters providing only mechanical filtration begin their life at their lowest particle removal efficiency and rely on the building of the dust cake in the filter to increase efficiency. 

In addition, the electrostatic effects created in an electret-charged filter media are particularly useful in increasing the capture efficiency for submicron particles. In fact, recent testing showed MERV 8 filter using electret-treated media performed on average 20 percentage points higher in E1 and E2 efficiency than mechanical filters on the market today. 

Plus, electret-charged filter media almost always delivers lower airflow resistance in the same filter construction as mechanical-only filter, especially those made of fiberglass. This translates into reduced energy consumption and costs. 

If you try to save money by reducing filter change-out frequency, you’re doing it wrong. Reducing the frequency of filter change-outs or downgrading to a lower priced air filter will not save money. In fact, the small amount of money saved by reducing or eliminating air filter purchases pales in comparison to the energy and operating costs that can be saved with a robust air filter maintenance and upgrade program. 

While purchasing fewer filters may reduce initial expenses, delaying filter change-outs also causes your HVAC system to run more days at peak airflow resistance and energy usage. It doesn’t take long for peak energy usage costs to offset any savings in the filter price. 

One way to lessen the frequency of and purchase costs related to filter change-outs is to choose a high-capacity pleated filter with an extended filter life that provides the desired filtration efficiency at the lowest possible airflow resistance.


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