- Filtration Concepts
With prices increasing, are you getting the most life out of your filters?
Updated: Jul 25, 2022
Prior to the pandemic prices had already started to be on the rise for HVAC filters. In the 5 years leading up to the pandemic, we saw prices surpass an overall 50% increase. And when the pandemic started pricing sky-rocketed with no clear vision of what the future will hold.
So with prices spiking, an uncertain future, and filters needing to be changed out, how can you make sure that you’re getting the most life out of your filters to where they last the longest in your units without compromising the indoor air quality of your facility?
There are two things to keep in mind when helping you accomplish this: Choosing the right filter and having the right schedule (frequency).
In regards to choosing the right filter, there are several factors that need to be considered. Those are MERV ratings, dust holding capacity (DHC), media quality, and average pressure drop.
Some of these may be a deal breaker for your institution and some may not be as important. But they all play an important role in how long the filter will last.
MERV stands for Minimal Efficiency Reporting Value and was introduced by ASHRAE in 1999. The 52.2 rating system for air filters rates all air filters on a scale from a MERV 1 to a MERV 16.
Anything over a MERV 16 is considered a HEPA/ULPA filter. You can read more about what the standards are for a filter to be considered a HEPA here.
MERV ratings tell you the particle removal efficiency for a filter across 3 ranges of microns (sizes of particles). And the higher the MERV rating the more efficient the filter is at capturing smaller particles. But keep in mind that the higher the MERV rating of a filter the more resistance to airflow it will be.
So when choosing a MERV rating, you have to make sure your unit is designed to handle that kind of resistance that comes with higher MERV-rated filters. Having a higher MERV-rated filter in a unit that can’t handle it will burn out the unit faster. And having too low of a MERV-rated filter can compromise the Indoor Air Quality (IAQ) of your institution as well as damage the integrity of the unit. Knowing the CFM of your units or the type of unit you have can help in determining the MERV range that it can handle.
In 2008 ASHRAE revised the 52.2 and updated it to the 52.2-2007 B which added 2 new elements on how a filter is rated. The first one is Dust Holding Capacity and the other is the Appendix J or MERV-A rating.
Dust Holding Capacity shows the amount of dirt/particles in grams that a filter can hold before the filter reaches the end of its life. The higher the DHC the longer the filter can last.
For instance, a 2” MERV 8 pleat has 81 grams of DHC and will last on average 3 months, depending on the application. But a 4” MERV 8 has a DHC of 142. This can extend the life of the filter by at least a month and a half maybe 2.
The second half of that 2008 revision is the Appendix J or MERV-A rating. When a filter is being made there is a natural electrostatic charge imposed in the media during manufacturing. This means that a filter may demonstrate a high efficiency when clean but drop in efficiency during its actual use cycle.
In the study below put out by VTT Finland Research Institute you can see that a brand new 12" filter is just under 60% efficient at the beginning of its life. But by the 2nd week, it's already under 40% efficient. At the end of its life at 52 weeks, it settled at just above 20% efficiency.
In other words, a brand new MERV 8 filter in your unit actually operates at a MERV 6 rating on average during its life. This is because the electrostatic on a brand new filter acts as a magnet when particles are passing through. It collects as much dirt as possible in the beginning. But once this “magnet” dissipates it drops in the number of particles it’s actually catching.
A-rated filters are manufactured without this electrostatic charge assuring that the filter will remain its intended MERV rating throughout its life while also maintaining its DHC. So if you’re needing a certain MERV-rated filter for a specific area or application having a MERV A-rated filter is the way to go.
Let’s go back to the 2” and the 4” MERV 8 example stated above. In our original scenario, we replaced a 2” MERV 8 filter (81 DHC) with a 4” MERV 8 filter (142 DHC). In this example, we were able to increase the life of this filter by about 1.5 months.
But if we made sure that the 4” filter was MERV-A rated, we’ve increased the DHC to over 200 grams and doubled the filter’s life to 6 months instead of 3. So we went from changing a 2” filter 4 times a year to changing the 4” filter 2 times a year.
Keeping these factors in mind when choosing your filters can reduce the amount you purchase in a year by up to 50%. The demonstration of the 2” and 4” filters is just one example of many on how the revision from ASHRAE now makes an even bigger difference in choosing the right MERV rating for your air filter for your facility.
The other factors that go into play when choosing the right filters include the quality/design of the media and the initial/average pressure drop of the filter.
The quality and design of the media can be anything from what the media is made out of to how tightly it is woven together, or how much media in square inches the filter has. And depending on the application the filter is being used, will determine the best filter media design.
The media and design have an effect on the filter's initial and average pressure drop. A lower pressure drop will bring a lower average pressure drop. The average pressure drop is used by ASHRAE when calculating the energy consumption of a given filter and also gives us a clue as to how long the filter will last.
You want to get as low of an average pressure drop as you can. This means the filter has a higher DHC, will last longer and will be less restrictive to airflow meaning it will cost fewer energy dollars.
To learn more about achieving sustainability through your air filters, click here.
So, we’ve covered some key factors on what to look for when choosing filters to help them last as long as possible. The other major decision to keep in mind to make sure you’re getting the longest life out of your filter is setting the right frequency or change-out periods for your filters.
Again, depending on the application that the filter is going to be used can sometimes dictate how long a filter can last. For instance, in most outside air applications, the filters probably need to be changed monthly, if not sooner. But if you take that same filter that is being used in the outside air unit and put it in a package unit on the roof, it can last on average 3 months.
With all the variables out there that can dictate the life of the filter, there are certain guidelines for determining a filter's life but it’s not as concrete as you would think. For instance, pleated filters can last anywhere from 1 month to 9 months. Again, depending on the factors stated above. 6” and 12” final, or second-stage filters, can last anywhere from 6 months to 2 years. HEPA filters can last anywhere from 2 to 5 years.
And it’s important to have the right frequency for your filters because if you leave them in their units past their life it will affect the quality of your IAQ, cause more stress on the unit, decrease the life of the unit, and increase energy costs. And changing a filter too early will cause you to buy more filters than you actually need.
So with such a wide range of frequencies per type of filter, how do you know which is the right frequency for the right filter?
In an ideal world, you would go off the Magnehelic readings that are attached to your AHUs. One, they don’t always work, two, not every unit has them installed. In all of the institutions we’ve visited, it is rare for a Magnehelic to work properly - even newly installed ones do not work like they’re supposed to.
Our clients enjoy the option of sending us their filters and having us test them in our Portable Test Lab. When we test filters in our Portable Test Lab we are able to see the pressure drop of the filter across various CFM rates. From this, we are able to determine if the filter has life left, or if it’s past its life and needs to be changed more often.
We create a data sheet that shows the results and send it to them. This is one way to know that you’re getting the most life out of your filter without guessing.
So to recap choosing the right filter and having the right frequency are important in prolonging the life of your filters. The best part in making sure you have the best filter for your units is that overall, it costs about the same if not slightly under or over what you’re already paying.
Although choosing filters that have higher DHC and MERV ratings costs more, you’re going to change them less often and the cost will balance itself out. So you’re buying fewer filters but they also last twice as long in most cases.
When we are done setting up a new client we produce a Green Initiative Analysis Summary for them that lets them know what options they have to go to a better, longer-lasting filter.
Below is an executive summary for a major university in the central United States that shows you the number of filters they were buying and the number of filters they are currently buying (see bottom left).
The numbers you see are only the filters we were able to make recommendations on. There were some units that were designed for a specific filter that we had no options for.
With our recommendations, they were able to reduce the number of filters they bought on an annual basis. They went from buying 9,070 filters to 4,051. That’s a 55% reduction. And even though they were buying a more expensive filter they were paying less over the course of a year because the filters lasted longer in the units.
When we set up a new client not only do they get the best recommendation for filter options but they also get their filters on a set schedule assuring the filter is changed out not too soon and not too late.
To learn more about our Filtrac Supply Program click here.
If you have any questions about how we can help you and your institution with your air filters, reach out to our sales team at email@example.com or 806-470-0099