Air filters are essential to achieve the expected air quality in commercial settings, public buildings, or many high-end manufacturing industries. The most critical thing here is designing and setting these filters in the filtration system to achieve the best effect.
As a professional air filter manufacturer, I have served many customers and used my knowledge and experience to help them design filters scientifically. In this article, I will list 7 tips on this.
1. Set proper air filter’s efficiency at different stages
Undoubtedly, the air filter’s filtration efficiency is the primary concern of all users. In many cases, you may need different levels of filters in your filtration system. They will form a multi-stage filtration to complete the air purification work.
Importance of pre-filter
Under normal circumstances, the last level of air filter determines the degree of air purification, and the primary level of air filters only plays a protective role. “They safeguard the subsequent filter to prolong its lifespan or shield the air conditioning system to maintain its consistent functioning.
In designing filtration systems, the effectiveness of the last air filter must be established first based on the cleanliness needs of the user. Subsequently, a protective filter should be chosen. If this air filter also needs protection, another filter should be added to the upwind end. The protective filters are collectively called “pre-filters.”
The efficiency of the filters at each stage should be appropriately matched. If two air filters in a row are very different in how well they clean, the first one can’t adequately protect the next one. But if they’re too similar, the second one only does a little more, which wastes money.
For example, the quality of the pre-filter is the most critical factor affecting the service life of the HEPA filter at the end of the clean room.
Tips for determining the efficiency of air filters at all levels
General guide
When using the “G~F~H~U” efficiency specification classification, the efficiency of the required filters at each stage can be easily estimated. In G2-H12, a filter is set every 2-4 steps. For example, G4-F7-H10, in which the terminal H10 (sub-high efficiency) filter determines the cleanliness level of the air supply, F7 protects H10, and G4 protects F7.
For cleanroom filters
The final HEPA filter in a clean room needs a filter rated F8 or higher for protection. An F9-H11 filter can go before the ULPA filter, which is even more efficient. The central air conditioning system should have at least an F5 filter to protect it.
Other occasions
In areas with no wind and sand and low pollution, there is no need to set up a pre-filter before the F7 filter; in urban central air-conditioning systems, G3-F6 is a common primary filter.
Case Study
A class 100 clean room is equipped with four-stage filtration of F5-F8-H10-H13, and the terminal H13 HEPA filter has been used for over 3 years.
There is only F5 filter protection in front of the HEPA filter in a clean room, and users must replace the HEPA filter every year.
The filter in a fresh air purification system in a heavily polluted city was set to G3-H10. The H10 filter was scrapped after half a month of operation.
Key points
The performance of the final filter must be reliable.
The efficiency specifications of the pre-filter should be proper.
Maintenance of the primary filter should be easy.
2. Pay attention to poplar catkins and willow catkins
Since ancient times, people have praised poplars and sighed willows. However, spring willow catkins are a disaster for filters, clogging any air filter that tries to block them.
In addition to willow catkins, there are many other plants with catkins. But those floating catkins are not as light and widespread as poplar catkins, and their impact on the filter is not that serious.
If you live in a place where willows are shady, you should take corresponding measures in the design of the air conditioner, such as changing the height of the air inlet or adding a protective net at the air inlet. If the measures are not taken properly, you have only one trick left: be diligent in the season of catkins. Change the filter.
3. Watch out for sleet and tree hangings
In the north, there may be an early spring morning when the drizzle forms thin ice on the ground. Some mornings, when the roads are slippery and dangerous, the filter will also fail.
The filter sees drizzle as particulate matter and blocks it, and the water droplets freeze at sub-zero temperatures and quickly seal the filter. At this point, any filter will give in.
If there’s a chance of freezing rain or tree hangings in your area, keeping a set of spare filters on hand for emergencies is a good idea.
4. The impact of persistent heavy fog
Fog is tiny water droplets that hit the filter and mix with the dust on the filter material to form mud. If the filter material is very fluffy, the mud will flow into the downwind end of the filter with the wind, and the filter can still be used. If the filter material is dense, mud will smother the filter.
For filtration or dust removal devices with pulse backflush dust cleaning function, the dust cleaning function will fail if there is mud on the filter material. It was fine for one or two days, but the trouble was that it was foggy for a week.
You may not believe it; the air filter is not afraid of continuous rain but of continuous fog. There is less dust on rainy days, and rainwater can be kept out of the air filter with some measures, so the air filter is not afraid of continuous rain.
There is not much dust on foggy days, but it puts extra pressure on the filter.
At this time, you may need a mist removal system to protect the filter.
5. Dealing with Hydrofluoric Acid
Hydrogen fluoride and water form hydrofluoric acid. Hydrofluoric acid is highly corrosive to glass. The HEPA filter material is glass fiber. However, hydrofluoric acid, which HEPA filters are most afraid of, will appear in some clean factories.
For example, in the manufacturing process of televisions and computer picture tubes, hydrofluoric acid is used to clean or curve the glass cover of the picture tube, and the cleaning work must be carried out in a clean factory equipped with a HEPA filter.
Although the concentration of hydrogen fluoride in the workshop air will be controlled within a relatively safe range, it is enough to damage the high-efficiency filter.
Some “screen cleaning” workshops use fresh air systems, but in other designs, the air conditioning system uses a large amount of circulating air to save energy. At this time, the thin glass fibers in the HEPA filter become a “fuse” for hydrogen fluoride.
In screen cleaning workshops with circulating air, problems or accidents have always been discovered. The scary thing is you can’t change the filter on the spot right away. We all know that replacing HEPA filters in industrial environments requires many measures.
Use PTFE HEPA filter
There is a new HEPA filter material, PTFE, that is not afraid of hydrogen fluoride, but if it is used in the above situations, it is equivalent to replacing the “fuse” with copper wire. HEPA filters are safe.
6. Prevent black stains from air vents
After installing a central air conditioner, people may see radiating black stains around the air supply vents.
Causes and phenomena
Dust particles diffused in the air may move with the airflow and cause irregular movement. When dust particles hit the wall, they are adsorbed by the wall due to van der Waals gravity.
The airflow velocity at the air outlet is high, and there are more opportunities for dust to hit the wall, so the air outlet gets dirty faster than elsewhere. When there is a temperature difference between the wall and the surrounding air, natural convection is formed, and this area gets dirty faster than elsewhere.
Near the air outlet, there is both forced convection caused by air supply and natural convection caused by temperature differences. If there is no good filter in the air conditioning system, the area around the air vents will be “dyed” black in as little as a few months or as long as two years.
Solution
The cause of black stains is dirty air. A good air filter in the HVAC system can prevent black stains.
Filters (colorimetric 85%, European specification F7) are preferred; if you pursue high quality, you can choose F8 filters. F6 and F5 filters are not enough to eliminate black stains, but they can delay their generation and spread.
Last summary
Besides the aspects highlighted in the article, the filter’s design must consider various factors like the environment it will be used, the cost of spare parts, energy usage during operation, and maintenance expenses. Nonetheless, the insights provided are grounded in practical experience; they aim to assist and inspire professionals and users.
