The COVID pandemic impacted the way many industries do business, and the HVAC industry is no exception. Ongoing concerns regarding infection risk and indoor air quality have prompted an unprecedented demand for filters with a Minimum Efficiency Reporting Value (MERV) value of 13, commonly known as MERV 13 filters, as well as those with even higher MERV ratings. As part of its COVID response, ASHRAE recommends increasing outside air within buildings as much as possible, as well as upgrading air filters to a minimum MERV 13 efficiency rating.
The rush to upgrade to high MERV filters, however, opens the door to a practical discussion about whether that is the best action in all cases. The reality is that using the wrong filter for the wrong application in the wrong place can substantially limit HVAC systems’ efficiency. The result is that air quality will suffer, and the system will consume more power than it should to function.
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A MERV rating is determined by the filter’s particle-size removal efficiency. The higher the number, the higher the filter efficiency. Before considering ratings, however, it’s important to determine the purpose of the filter.
If the primary purpose is to keep heating and air conditioning systems clean and block contaminants from interfering with the operation of key components, you likely don’t need as high a MERV rating. If the primary objective is to protect breathing air quality, then a higher MERV rating might make sense.
An option worth considering in some applications is the use of a multi-filter system that includes final filters and pre-filters. A less expensive, lower MERV-rated filter, functioning as a pre-filter, can trap dirt and large particles before the air reaches the final filters downstream which then remove the small particles. Multi-filter systems can extend the life of the more expensive final filters, creating overall cost savings.
When choosing a filter, it’s also important to consider the conditioned space’s activities and the types and sizes of particles those activities generate. Contaminants of greatest concern need to be evaluated to determine the level of filtration efficiency required for that contaminant’s size (measured in micrometers/microns). Once a full list of contaminants of concern has been identified, you can use the ANSI/ASHRAE Standard 52.2-2017 to select the proper filter with the appropriate MERV.
Of course, particle-capture efficiency matters. But there are also other filter characteristics that should be considered when determining the best filter for a specific application. Cost is always a consideration and should include the purchase price, as well as service life and maintenance requirements. The filter’s resistance to airflow also is a key consideration, as it is proportional to the energy consumed by the filter. Energy expenditures can account for about 81% of an air filtration system’s annual operating costs, while its purchase price and maintenance can account for about 18.5%.
Other considerations include the design and materials used in filters. Some designs are easier to install, seal better, and don’t absorb moisture or shed. Pleated filters, which are commonly made with a blend of cotton and polyester or synthetic media, provide a larger filter-surface area than panel filters. Most pleated filters are MERV 6 to 13. Depending on the filter, capture efficiencies for particles in the 3 to 10-micron range can be 35% to 90%.
There are also extended-surface filters that are made with synthetic, fiberglass or cellulose/glass-fiber media. These include bag or pocket, rigid-cell, aluminum-separator and V-bank filters. Pocket filters provide an even greater filter surface area than pleated filters to provide maximum efficiency with the lowest pressure drop and longest life. They typically have MERV ratings of 11 to 15.
Even a filter with the highest MERV rating can’t achieve high-quality air if some of the air is not going through the filter. Gaps around high-efficiency filters or filter housings can decrease filter performance. They occur when filter media are not sealed properly in the filter frame, when filters are not gasketed properly in filter racks, or when air-handler doors and duct systems are not sealed properly.
For a 1-mm gap, bypass flows can increase to 25% to 35% of the total airflow. The percentage increases based on the filter’s efficiency because air naturally flows through areas with the least resistance. Since higher efficiency filters have a greater resistance to airflow, bypass air has a larger effect. This, in turn, reduces the efficiency rating. For a 1-mm gap, for instance, a MERV 15 filter will perform only as well as a MERV 14 filter. A 10-mm gap, in contrast, causes a MERV 15 filter to perform as a MERV 8 filter. That’s why building operators and maintenance personnel should perform regular field inspections to ensure filter seals and gaskets are installed properly.
To combat gap problems, Parker created its QuadSEAL® HVAC filters with proprietary E-Pleat® media technology. The molded polyurethane frame incorporates a QuadSEAL integrated gasket on all four sides and can flex without damage. Since the media pack is 100% bonded into the foamed frame, bypass is eliminated as is the need for additional sealants or adhesives.
If it were just a matter of choosing the filter that produced the best air quality, the decision would be simple. Everyone would install filters with the highest MERV ratings they could find. Unfortunately, it’s not quite so simple. The challenge facing engineers, building owners and maintenance personnel tasked with specifying and installing filters is that more efficient filters cause higher pressure drops because the smaller pores create more resistance to air flow.
Not only are higher efficiency filters less energy efficient (causing increased energy consumption by the fan), but your air handling unit simply may not have enough capacity to function with a high-efficiency filter. The reality is that most commercial HVAC systems today can only handle MERV 8 filter or MERV 9 filter types.
So, what are your options?
When COVID hit, suddenly industries that, for years, had functioned well with filters with MERV ratings of 8, 10 or 11, were scrambling for MERV 13, 14 and 16 filters. The reality, though, is that there are filter options even more efficient than MERV 16 filters.
High Efficiency Particulate Air (HEPA) and Ultra-Low Particulate Air (ULPA) filters are designed to trap the smallest airborne particles and contaminants. HEPA filters have a minimum efficiency of 99.97% at 0.3 microns, whereas ULPA filters have an efficiency rating of 99.999% at 0.12 microns or higher. This does not mean that ULPA filters are better than HEPA filters when taking air flow and other variables into account. In fact, HEPA filters cost less, have a lower resistance to air flow and offer a longer service life than ULPA filters.
Parker offers a complete line of HEPA and ULPA standalone and pre-filters for removing particles and contaminants with efficiencies up to 99.9995%. They also are designed to reduce energy consumption and operating costs.
So why doesn’t everyone simply switch to a HEPA or ULPA filter since they represent the gold standard in air quality? Because most commercial and industrial HVAC systems on the market today simply aren’t compatible with them. Since they are so efficient, HEPA and ULPA filters cause a higher pressure drop than filters with lower MERV ratings.
The best option today for using HEPA and ULPA filters is as part of stand-alone systems. Many school districts are looking at options for installing portable air filtration systems with HEPA filters in each classroom to augment their central air filtration systems. HEPA and ULPA filters are also frequently found in critical medical applications and cleanrooms.
Parker’s approach to balancing the need for efficiency with minimum pressure drops has been the development of its LoadTECH® filter that utilize Parker’s proprietary E-pleat® technology. This patented design molds filtration media into a series of pre-formed channels that direct the air smoothly through the filter, allowing for even loading, minimum resistance and complete media utilization. The previously mentioned QuadSEAL® filters offer a similar benefit of improving efficiency without restricting air flow. The advanced media used in these filters also resists tearing, damage, moisture and microbial growth, leading to a long filter life and the need for fewer filter changeouts.
The decision to use a filter with a MERV 13 rating (or higher), in accordance with the latest guidance from the Centers for Disease Control (CDC) and ASHRAE, is complicated by the fact that most commercial HVAC systems cannot handle the highest efficiency-rated filters. While there are options for upgrades, redesigns that include a multi-filter system, and new technologies that balance efficiency and air flow, specifiers need to be careful that they choose the right filter after considering all the variables, including cost, maintenance requirements, operating efficiency and, of course, air quality.
Recent events and trends have challenged the HVACR industry to respond with technological innovations much more quickly than ever before. To learn more, download our white paper on innovations and trends in HVACR.
This article was contributed by the Parker HVAC Filtration Division.