5 Steps to Upgrade HVAC Filtration
Here are five best practices to reduce HVAC maintenance, improve indoor air quality, and provide several other HVAC-related benefits.
Upgrading filtration may be the most cost-effective way to clean up indoor air or contaminated outdoor air, but operators should consider the following costs when making decisions:
- Cost of consumables – higher MERV filters are more expensive
- Cost of more maintenance – higher MERV filters need to be replaced more often
- Equipment upgrade costs – higher MERV filters can damage existing equipment
The following steps are more or less recommended, from the cheapest option to the most expensive. Keep in mind that indoor air quality (IAQ) budgets should be reasonable based on the nature and severity of the problem.
Step 1: Assess your current filtration equipment and maintenance programs. Air filtration is a support function of most modern HVAC systems, and while upgrading to higher efficiency filters can be a cost-effective option, a detailed examination of existing equipment and operation should be performed. Operators must first verify that simply revising protocols and procedures can achieve their goals. Existing equipment and filter grades may prove sufficient with complementary strategies, such as: changing control options for extended fan run times, including occupied pre- and post-purge of building air flushes and filtration fans; increasing the frequency of filter changes along with channel cleaning, checking and adjusting filter fit and sealing to prevent bypass.
Step 2: Is it possible to upgrade filters in existing equipment and achieve better performance without the need for other changes? In other words, can installed equipment handle higher quality filters without modification? When making assessments, keep in mind the additional strategies listed in Step 1 above. All filters cause a restriction of the airflow. Higher efficiency filters of the same type add more constraints as the MERV rating increases. This requires careful evaluation during the upgrade selection process, as an excessive increase in static pressure can cause damage to some air handling equipment and reduce heating and cooling performance. It is important not to assume that a higher MERV is always better. Higher MERV filters will increase the initial pressure drop and will contain dust and particulates more quickly than the less efficient filters, requiring more frequent filter changes.
When considering a filter upgrade or equipment change, operators should obtain as much detail as possible about the existing equipment and operational specifications. Ideally, there are Test Adjust Balancing (TAB) records from the original Commissioning Agent and additional reports of any subsequent adjustments and changes. These records will be invaluable in the future as they will help determine what additional capacity may be available with the existing equipment and give designers a baseline of performance to work from. Have a qualified TAB technician check the system to ensure current performance matches historical TAB information. Have them recheck and rebalance the system after any changes are made to ensure that the changes made are compatible with the equipment and that performance has not deteriorated.
Keep in mind that a change in filter type can prevent static pressure issues. For example, if you switch from a flat panel filter to a pleated filter, you can increase the MERV without a significant static pressure drop. Part loading can actually increase the efficiency of a filter, but careful monitoring of the filter pressure drop should be a part of any maintenance program. Whenever filters are upgraded, there needs to be more oversight. Maintenance personnel should be provided with test equipment and trained to measure the progressive pressure drop across upgraded filters. Digital pressure gauges or low pressure gauges can be used to establish new replacement schedules. High-performance air handling equipment may already include filter monitoring equipment, making it easy to detect the need for filter replacement by on-site personnel or through a building management system. This solution is highly recommended to prevent equipment wear, indicate when an unusual situation has caused an unexpected blockage, or help avoid the cost of unnecessary filter changes.
Step 3: Is it possible to upgrade existing equipment to accept higher quality filters? Existing equipment may have airflow limitations, but there may be relatively inexpensive ways to make changes. It is often possible to increase fan speeds to overcome higher static pressures and provide the same airflow, provided the fan motor can handle the additional electrical load. Consult equipment manufacturers or I&D manuals to see if this is a viable option.
Filter racks can often be modified or replaced to accept lower pressure drop sizes. In general, upgrading to a deeper pleated filter will give you a higher MERV without a big pressure drop penalty. Commercial equipment often comes standard with 2-inch filter racks. If a 2-inch pleated filter is too limited, it may be easy to upgrade the filter rack to accept a 4- or even 6-inch filter. Consult an air filter specialist or commercial filter manufacturer or supplier to see what options are available. An alternative filter size may be available to suit your equipment. For larger buildings or multiple projects, it makes sense to hire a mechanical engineering consultant to help evaluate existing equipment and come up with practical solutions.
Step 4: Adding equipment may be necessary if existing equipment cannot solve the IAQ problems. Due to the recent air quality calamities, many stand-alone “air scrubber” devices have been developed and marketed. They are intended to provide air cleaning solutions, usually for individual rooms, but some can be connected to central systems to add enhanced filtration. Popular sizes include: freestanding units (fixed or movable), ceiling mount, duct mount, duct bypass, cabinet or alcove installed and many more. Typically, these units use a very high (MERV 13 to HEPA) air filter and a built-in fan. Noise complaints are common, but high-quality units intended for use in classrooms and offices will be fitted with acoustic cladding, quiet ECM fans and advanced controls. Research the manufacturer’s literature for decibel ranges and levels.
Air filtration is a proven way to reduce pathogen concentration and residence time, but will not kill pathogens on its own. Many air scrubbers are available that add UV-C light disinfection and/or bipolar ionization chambers to the HEPA filter, but caution is advised. Air and surface disinfection with UV-C germicidal light has been used for years and is recommended by ASHRAE and the US Centers for Disease Control and Prevention (CDC) when applied correctly. CDC has neither recommended for nor against bipolar ionization, but the technology is known to be effective in the right applications. These units must be certified to UL 2998 “Standard for Zero Ozone Emissions from Air Purifiers.” Consumers are urged to do their homework when considering these devices, and must request performance data from multiple sources in order to make a valid assessment.
Step 5: New equipment. By replacing equipment and redesigning the system, as well as purchasing equipment for new facilities, building owners can meet filtration requirements with fewer compromises. Commercial air handling units are normally highly customizable and can be ordered with much improved filtration options with air-moving components that can handle the additional loads that can arise. Rather than filtration being an afterthought, equipment can be designed from the ground up with options such as larger filter racks, pre-filters, variable speed fans to respond to filter loading, control options to monitor pressure drop, airflow sensors, duct design or redesign for better recirculation and build flush — there are many possibilities. Again, consulting with a team of the mechanical engineer, IAQ professional, filtration specialist and equipment manufacturers will help come up with effective solutions and likely save money in the long run. The team must take your budget into account. In some cases, when all is said and done, they can come up with the most cost-effective solution of all and advise you to just open the windows from time to time.
This article is an excerpt from the eBook, “How to Improve Indoor Air Quality with Effective Air Filtration.” The full eBook can be read with a membership to FMD’s premium content product, fnPrime.
Roy Collver has over 40 years of experience in the HVAC industry. He specializes in hydronics, with a strong focus on boiler technology, control and gas combustion. In addition to writing and training, he works in construction administration for mechanical engineering companies.