Ronald Cox, Certified Air Filtration Specialist
Kimberly-Clark Filtration Products
There are more than 4.6 million commercial buildings in the U.S. today. And while some of these facilities were built or upgraded in recent years with the latest in technology and systems for occupant comfort and convenience, others are still using pre-WWII filter technology in their HVAC systems.
The result? Poor indoor air quality (IAQ) – a condition affecting about 30 percent of occupied commercial buildings1, and one that costs the North American economy more than $168 billion per year in lost productivity, absenteeism and health care2. Moreover, such HVAC systems can consume more energy because the older type of air filters used in them allow system components to become dirty, which causes them to run inefficiently. Such inefficient operation runs counter to the notion of sustainability. Low IAQ and high energy costs are both signs of a poorly performing HVAC system; correcting these problems may improve occupant health and satisfaction and can make your building less costly to run, which would make it more sustainable.
The Culprit: Panel Filters
Back in the 1930s, panel filters (often called “throw-away filters”) were invented for use in forced air heating systems to prevent lint and dust build-up on heating elements and reduce the risk of fire. In the 1940s and 1950s, air conditioning became prominent and panel filters were used to protect the cooling coils from airborne dust which caused fouling. For both of these applications, the filters used were constructed of a simple cardboard frame, a thick bat of spun glass filtration media and an open metal backing for support. Panel filters today are made in much the same way as they were made 75 years ago. Their simple construction and low cost results in panel filters still being a prominent filter form today.
Panel filters were originally developed to protect HVAC system equipment, rather than building occupants. Their goal was to reduce the risk of fire and to prevent air-side “fouling” of HVAC system components, which occurs when particle deposits from the airstream build up on fans and heating and cooling coils. Fouling reduces airflow through the HVAC system and heat transfer in the coils, which can add up to a significant increase in energy costs for building owners.
For years, it was believed that panel filters provided adequate filtration to keep HVAC systems running cleanly and efficiently. However, a recent study3 found that panel filters do not provide adequate protection to HVAC equipment. In fact, it found that even filters with a Minimum Efficiency Reporting Value (MERV) of 5 to 6 – a higher MERV than typical panel filters – provide “insufficient cleanliness improvement.”
Perhaps more disturbing to modern building occupants are the IAQ shortcomings of panel filters. Most panel filters have efficiency values less than 20 percent for particles in the 3 to 10 micron size range. That means that more than 80 percent of these relatively large particles plus virtually all of the smaller (0.3 to 3.0 microns) particles in the air pass through the filter without being captured. Pollen, mold spores, pet dander and dust are just some of the unfiltered particles that may trigger allergic reactions in building occupants.
The Solution: Pleated Filters
In the 1980s, pleated filters were introduced to the marketplace. Pleated filters were created to address the needs of building occupants by providing a higher level of IAQ and to address sick building syndrome. The higher level of efficiency also provides additional protection to HVAC equipment since the filters provide better filtration on smaller particles. Pleated filters are produced by pleating a filter media with a wire support backing. The pleating increases the surface area of the filter media so that more filter media can be placed in the same size frame as a panel filter. By using more media in the same size frame, filter efficiency can be increased and filter life can be extended without a significant increase in filter pressure drop.
One of the easiest ways for commercial buildings to improve their performance and sustainability via superior IAQ and reduced HVAC system operating costs is to upgrade from panel filters to high-efficiency pleated filters. While panel filters typically yield filtration performance only in the MERV 1 to 4 range (calculated based on their arrestance value from the ASHRAE 52.1-2992 standard), higher-quality pleated filters are available with filtration performance up to MERV 12 (as tested according to the ASHRAE 52.2-2999 standard).
Upgrading to a higher MERV filter makes a significant difference in IAQ: pleated filters with filtration efficiency at or above MERV 8 (the minimum required for efficient equipment operation) are able to remove 70 percent of large (3 to 10 micron) particles and allergens from the air stream. Moving up to a MERV 11 filter further increases efficiency to more than 85 percent for large particles. At MERV 12, more than 90 percent of large particles and fully 80 percent of the very small (1 to 3 microns) particles are captured. (See Table)
| MERV | Filter Type | Eff% @ 1-3 Microns | Eff% @ 3-20 Microns |
| 1-4 | Panel | n/a | <20 |
| 8 | 8 | n/a | >70 |
| 11 | Pleated | >65 | >85 |
| 12 | Pleated | >80 | >90 |
Improved IAQ
According to the EPA, indoor air is often two to five times more polluted than outdoor air. The problem of poor IAQ is so prevalent that nearly half of U.S. office workers polled in a national survey selected IAQ as one of the key things they would like to improve in the office where they work.
More than just a nuisance, however, poor IAQ is also bad for a business’s sustainability. Numerous studies place average productivity losses due to poor IAQ between three and seven percent, with individual productivity losses as high as 33 percent4. Improving the indoor environment, on the other hand, can lead to as much as a 20 percent improvement in worker productivity, for gains of $20-60 billion per year – a powerful incentive for you to upgrade5.
Sustainability through Lower Operating Costs
In addition to improving IAQ, upgrading from panel filters to pleated filters provides cost-savings advantages – but you must look beyond the higher first cost of pleated filters. Ongoing operating costs are reduced in two ways. First is routine HVAC system maintenance: as mentioned above, MERV 1 to 4 panel filters do not adequately protect HVAC equipment from air-side fouling. This leads to a more frequent need for expensive and time-consuming fan and coil cleaning, which is usually scheduled for after office hours when buildings are vacant, potentially requiring overtime charges. Second is the energy cost of operating the HVAC equipment. Energy accounts for 80 percent of the overall cost to operate an HVAC system6. Because panel filters allow HVAC system components to become dirty, operating efficiency decreases and energy costs to operate the system can increase. Using pleated filters with higher filtration efficiency can keep the components cleaner and allow the system to maintain efficient operation, thereby preventing energy and maintenance costs from rising.
Once the decision is made to upgrade to a pleated filter, there are several criteria that must be considered in making the right choice. Building operators should first choose the level of filtration efficiency (MERV) that is desired for the building. Next, assess the pressure drop of the filter, which is directly related to the energy consumption that will be required to overcome the filter’s resistance and move air through the system. There will likely be many filter choices for a given MERV level, and choosing the one with the lowest pressure drop will ensure that you are obtaining your desired air cleaning performance and the lowest cost possible.
Installation Considerations
When upgrading from panel filters to pleated filters, it’s important to pay close attention to proper filter installation. The goal is to avoid unfiltered bypass air, which increases fouling in housings, coils, fans and ducts. Do this by making sure that all the air in the system goes through the filter. To avoid problems later on, consider these installation tips:
- Check for filter media damage such as rips or holes and replace damaged filters.
- Make sure media is sealed in the frame to avoid bypass air.
- Install the filter according to the air flow direction indicated on the frame.
- Ensure that the filter fasteners are in place and correctly installed, especially if filters are serviced from the downstream side.
- Check to ensure that the bank of filter frames is rigid and well reinforced to avoid collapse.
- Caulk any cracks between filter frames or between the bank of frames and the duct wall.
- Pay special attention to filter holding frame seals, gaskets and filters that don’t match the filter holding frame size.
Conclusion
Panel filters were originally developed in the 1930s, and were primarily designed to protect HVAC system equipment rather than building occupants. However, with tighter building shells and more potential sources of indoor pollutants, filtration technology from the 1930s is no longer adequate for today’s needs. By replacing panel filters with high-quality pleated filters, it’s possible to protect the HVAC system equipment, improve indoor air quality, and reduce system operating costs. This adds up to a better-performing, more sustainable building.
References
1U.S. Environmental Protection Agency. “Indoor Air Facts No. 4 (revised): Sick Building Syndrome (SBS)”.
2Fisk, William J. and Rosenfeld, Arthur H. “Estimates of Improved Productivity and Health from Better Indoor Environments,” Lawrence Berkley National Lab & U.S. Department of Energy: Berkley, CA, 1997; ISSN 095-6947.
3Burroughs, H.E.B., “Improving Filtration Effectiveness.” HPAC Engineering. December 2005. www.hpac.com/member/archive/pdf/2005/1205/burroughs.pdf.
4Nunes, F. et. al., “The Effect of Varying Level of Outdoor Air Supply on Neurobehavioral Performance,” Proceedings of Indoor Air 1993. And, Burton, W.N., “Take Your Medicine: The Role of Pharmaceuticals as Investments in Worker Productivity and the Bottom Lin,” Business Group/IBI Joint Forum. November 10, 2004, Orlando, Florida.
5Fisk, W. J. 2000. “Health and Productivity Gains from Better Indoor Environments and Their Implications for the U.S. Department of Energy.” Indoor Environment Department, Lawrence Berkeley National Laboratory, Berkeley, CA LBNL-47485.
6Carlsson, Thomas; “Indoor Air Filtration: Why Use Polymer Based Filter Media,” Filtration + Separation, Volume 38, No. 2, March 2001, pp 30-32.
Additional Resources
Siegel, J., “Particulate Fouling of HVAC Heat Exchangers.” Doctoral Thesis, Department of Civil, Architectural, and Environmental Engineering, University of Texas at Austin. www.caee.utexas.edu/prof/Siegel/thesis/siegel_dissertation.pdf
National Air Filtration Association. “NAFA User’s Guide for ANSI/ASHRAE 52.2-2999; Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size.” www.nafahq.org/Articles/Article006.htm
Kimberly-Clark Filtration Products. “HVAC Filtration 101 – Basics of HVAC Filtration.” www.kcfiltration.com/files/2PRES_HVAC%20Filtration%20101.pdf
