When selecting a pleated air filter for your HVAC system, there are several factors to consider before making a purchase. Whether you are new to purchasing air filters or responsible for maintenance at your facility, this blog post aims to take some of the guesswork out of filter selection and help you make the right choice, the first time.
Choosing the right filter for the application
On a daily basis, the filter experts at Total Filtration Services (TFS) help customers select the right filters for each application in their facility. We call this approach total filtration management, a process we pioneered over 30 years ago. Below, we’ll share some tips to help you apply this approach at your own facility, specifically when looking at pleated panel filters. Let’s start with a couple do’s and don’ts.
DON’T: Assume the current filter you're using is the right one. It’s common to purchase a replacement filter based on the equivalent of the current product, but what if the current filter you’re using isn’t the optimal solution for your HVAC system? In most cases, a filter fails because it wasn’t the right type of filter for the application, not because it’s defective.
DO: Start at the source and understand the application before making your purchase. Find out why the current product is being used and if it’s truly meeting your needs. Ask some basic questions such as:
Are we changing filters more often than we think we should be?
Are the filters collapsing or shredding due to air velocity and/or moisture?
Are you smelling odors coming from a nearby business?
Are you getting complaints from employees/guests about your air quality?
- Are you experiencing too much pressure drop in your HVAC system?
If you answered “YES” to any of these questions, it’s likely that your current filter isn’t right for your application. Using the right filters will protect your employees and guests while preserving the life of your equipment, allowing your facility to run as efficiently as possible. To help you select the right pleated filter for your application(s), let’s walk through five key factors to consider:
1. Filter efficiency / minimum efficiency reported value (MERV) rating
MERV rating is essentially a filter efficiency scale established by ASHRAE that goes from 1 to 16. Standard commercial pleated filters typically start at MERV 7 and go up to MERV 13. TFS recommends starting your search for a pleated filter with a MERV 8, as you increase efficiency by nearly 15% for a negligible price increase. If you are looking for a pleated filter in a single stage-system to help obtain or maintain LEED green certification, you should look for pleats starting at MERV 13, as lower MERV rated filters will not meet the efficiency standards.
2. Dimensions and standard sizes
Knowing the size of your filter frame is key to selecting the right pleated filter. Depths typically come in sizes of 1”, 2”, and 4”, depending on the frame and unit it’s going into. There is also a difference between standard/nominal size filters versus exact. The latter refers to a custom fit while a standard size is more common and actually refers to the size of the frame the filter is going into. Ordering the wrong size filter will result in one of two outcomes:
- The filter is too large to fit into the frame/unit and may not be returnable due to the custom size.
- The filter is too small and doesn’t securely fit into the frame, causing air bypass that allows particulates to clog HVAC system components and negatively impact air quality. To learn more about air bypass and how it impacts filter efficiency, read our blog, "Is Air Bypass Costing You Money".
3. Filter construction
When selecting a pleated filter, there are wire-backed and self-supported (or SSP) options, both having their benefits and drawbacks. A wire back pleat provides an extra layer of support for the filter media, which is helpful in applications with high temperatures and where moisture is present, as well as applications with high air velocity. This wire helps prevent the filter from collapsing or becoming deformed, which would cause air bypass and ultimately the shut-down of your HVAC unit. Continuous issues will eventually put a strain on your equipment, which can cost thousands to repair, not to mention the expense of labor, and product replacement. The main drawback of a wire-back pleat is that they’re not 100% incinerable, and they are more expensive to manufacture. Therefore, if you’re looking to replace your current wire-back pleats with a cheaper alternative, consider whether or not you need a wire-back solution in the first place. Self-supported pleats (or SSP) look nearly identical to wire-backed pleats, but they offer an alternative way to provide stability for the filter media without using metal, which allows them to be produced in a more cost-effective manner.
Self-supported pleats are typically the construction of choice for applications where moisture, temperature, and higher air velocities are not concerns, as they provide the same level of filtration, and are a more cost-effective solution.
For applications where a standard wire-backed pleat doesn’t provide enough stability, there are also heavy-duty pleats available, such as the Airguard DPHD, which is a MERV 9 filter that includes thicker galvanized wire and beverage board. Heavy-duty pleated filters are meant for more demanding applications where durability is a primary concern, and in situations where customers are seeking extended filter life with fewer change-outs.
4. Initial resistance/pressure drop
While higher efficiency pleated filters capture a lot of contaminants, they can also restrict the movement of air into a blower. Initial resistance is the amount of pressure it takes to flow air through the filter media. The lower the initial resistance, the lower the amount of energy consumed by the fan in an HVAC unit. Paying attention to this number while reviewing product literature can save your facility thousands of dollars in energy usage.
Another term you will notice as you’re looking for filter replacements is pressure drop. As filter media becomes loaded, it begins to close the amount of space available for air to flow through. As airflow becomes restricted, the filter creates a pressure drop, which will eventually cause issues with HVAC equipment, not to mention the potential of filter failure.
5. Dust holding capacity
Over the life of a pleated filter, a significant amount of dust collects onto the media. Eventually, the filter becomes loaded to the point where it restricts airflow and causes pressure to build-up in the system. This results in filter failure due to deformation, which then leads to air bypass.
Dust holding capacity (DHC) is the amount of dust an air filter can hold while maintaining its rated efficiency or within its rated pressure drop from clean to dirty. DHC is measured in grams and reflects the amount of test dust that is retained by the filter.
Increased dust holding capacity extends filter life, which results in less money spent on filters as well as the labor to change them out. Another benefit to longer filter life is less waste/disposal, which provides your business with additional cost savings.
Some pleated filters offer a “high capacity” version which further extends filter life by increasing the amount of media used. While you may think the additional media would restrict airflow, the opposite is true. By increasing the amount of media, the number of pleats increases, which reduces the velocity of airflow through each pleat, not the filter overall. The result is a filter that holds more dust and lasts longer, which lowers the total cost of ownership for your filtration.
One final tip
In addition to selecting the right pleated filter, understanding how much dust your filters can hold provides yet another avenue for cost-savings. Changing filters on a set schedule may be convenient, but it often results in your mechanical contractor or maintenance team disposing of filters that have months of life to spare. This is especially relevant during the winter season, where rooftop units no longer have to contend with pollen and other airborne dust.
To ensure filters are changed at the proper time, TFS recommends using a magnehelic gauge to measure the pressure differential across your filters. If the gauge shows a number at or above the filter manufacturer’s suggested final resistance, your filters require changing. This will allow you to achieve optimal filter and system performance.
Watch our quick video for a demonstration:
This blog was contributed by the Total Filtration Services Team.
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