5 steps to upgrade HVAC filtration
Here are five best practices for reducing HVAC maintenance, improving indoor air quality, and providing several other HVAC-related benefits.
Improving filtration may be the most cost effective way to clean 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
- Increased maintenance cost – higher MERV filters need to be replaced more frequently
- Cost of equipment upgrades – higher MERV filters can damage existing equipment
The following steps are more or less recommended, from the cheapest to the most expensive options. Keep in mind that indoor air quality (IAQ) budgets should be reasonable based on the nature and severity of the problem.
Step 1: Evaluate your current filtration equipment and maintenance programs. Air filtration is an ancillary function of most modern HVAC systems, and while upgrading to more efficient filters can be a cost-effective option, a detailed investigation of existing equipment and operation should be undertaken. . Operators should first check whether the simple review of protocols and procedures can achieve their goals. Existing equipment and filter qualities may be adequate with complementary strategies such as: changing control options for longer occupied fan run times, including building air purges before and after purging and operation of filtration fans; increase the frequency of filter changes as well as duct cleaning, check and adjust filter fit and tightness to prevent bypass.
2nd step: Is it possible to upgrade the filters of existing equipment and achieve better performance without any further modification being required? In other words, can the installed equipment handle higher quality filters without modification? When performing assessments, keep in mind the additional strategies listed above in step 1. All filters have airflow restriction. Higher efficiency filters of the same type add more restrictions as the MERV rating increases. This requires careful evaluation during the upgrade selection process, as an excessive increase in static pressure can damage some air handling equipment and degrade 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 they will charge up dust and particles faster than less efficient filters, requiring more frequent filter changes.
When considering a filter upgrade or an equipment change, operators should obtain as much detail as possible about existing equipment and operational specifications. Ideally, there will be Balance Adjustment Test (TAB) records from the original commissioning agent and additional reports of all subsequent adjustments and changes. These records will be invaluable in the future, as they will help determine what additional capacity might be available with existing equipment and give designers a performance base from which to work. Hire a qualified TAB technician to perform a spot check of the system to ensure that current performance matches historical TAB information. Have them recheck and balance the system after making any changes to ensure that the changes made were compatible with the equipment and that operation was not degraded.
Keep in mind that changing the type of filter can prevent static pressure issues. Switching from a flat panel filter to a pleated filter, for example, could allow you to increase the MERV without adding a significant static pressure penalty. Partial load can actually increase the efficiency of a filter, but careful monitoring of the filter pressure drop should be part of any maintenance program. A higher level of control should be implemented each time the filters are upgraded. Maintenance personnel should be equipped with test equipment and trained to measure the progressive pressure drop across the improved filters. Digital manometers or low pressure gauges can be used to establish new replacement schedules. High-end air handling equipment can already be fitted with filter monitors, making it easier to detect the need for a filter change by on-site personnel or through a building management system. This solution is highly recommended to help prevent equipment wear, indicate when an unusual situation has created an unexpected blockage, or help avoid the expense 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 modifications. It is often possible to increase the fan speed to overcome higher static pressures and provide the same airflow, provided the fan motor can withstand the additional electrical load. Check with equipment manufacturers or I&O manuals to see if this is a viable option.
Filter holders can often be modified or replaced to accommodate lower pressure drop formats. In general, upgrading to a deeper pleated filter will give you a higher MERV without a large pressure drop. Commercial equipment often comes standard with 2 inch filter brackets. If a 2 inch pleated filter is too restrictive, it may be simple to upgrade the filter holder to accept a 4 or even 6 inch filter. Consult an air filter specialist or a commercial filter manufacturer or supplier for available options. There might be another filter format available that will work with your equipment. For larger buildings or multiple projects, it would be wise to hire a mechanical engineering consultant to help evaluate existing equipment and find practical solutions.
Step 4: Addition of equipment may be necessary if existing equipment cannot resolve IAQ issues. Many stand-alone “air cleaner” devices have been developed and brought to market due to recent air quality disasters. They are intended to provide air purification solutions primarily for individual rooms, but some can be connected to central systems to add improved filtration. Popular formats include: Free-standing units which are freestanding (fixed or mobile), ceiling mounted, duct mounted, duct bypass, installed in a closet or alcove, and many more. Typically, these units use a very high air filter (MERV 13 to HEPA) and a built-in fan. Complaints about operating noise are common, but high-quality units intended for classroom and office use will come with acoustic liners, quiet ECM fans, and sophisticated controls. Examine the manufacturer’s literature for decibel ranges and levels.
Air filtration is a proven way to reduce the concentration and residence time of pathogens, but will not in itself kill pathogens. There are many air cleaning units available that add UV-C light disinfection and / or bipolar ionization chambers to the HEPA filter, but caution is in order. Disinfecting air and surfaces using UV-C germicidal light has been used for years and is recommended by ASHRAE and the U.S. Centers for Disease Control and Prevention (CDC) if it is is applied correctly. The CDC has recommended neither 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 Emission for Air Purifiers“. Consumers are advised to do their homework when considering these devices and should request performance data from multiple sources in order to make a valid rating.
Step 5: New equipment. Equipment replacement and system redesign as well as the purchase of equipment for new installations allow building owners to meet filtration requirements with less compromise. Commercial air handling units are normally highly customizable and can be ordered with many enhanced filtration options with air displacement components that will support the additional loads that may result. Instead of filtration being an afterthought, equipment can be designed from scratch with options such as larger filter racks, pre-filters, variable speed fans to meet filter loading, options control to monitor pressure drop, air flow sensors, design or redesign of ducts for better recirculation and building flush – there are many possibilities. Again, consulting with a team of mechanical engineers, IAQ professionals, filtration specialists, and equipment manufacturers will help find effective solutions and possibly save money in the long run. The team should keep your budget in mind. In some cases, at the end of the day, they may come up with the most cost-effective solution of all and advise you to just open the windows every now and then.
This article is an excerpt from the eBook “How to Improve IAQ with Efficient Air Filtration”. The entire eBook can be read with a subscription 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 particular focus on boiler technology, controls and gas combustion. In addition to writing and training, he works in construction administration for mechanical engineering firms.