How to choose ULPA in high humidity environment?

When choosing ULPA in a high-humidity environment, the most common approach is to ask the supplier, 'How high a humidity can your filter element endure?' The answer is often a range of values. But this number is actually not enough to support the selection judgment.

What really affects the filter is not the reading on the hygrometer, but in what form, at what time, and where the moisture comes into contact. Continuous high humidity and short-term condensation are two different things, as are high ambient humidity and direct contact of the filter material with water. Only by looking at these types of situations separately can the direction of selection be clear. For specific material comparison, please refer to the relevant instructions for selecting glass fiber and PTFE filter materials.

First distinguish between humidity and condensation

High humidity is not necessarily a problem, condensation is often the start of trouble.

Continuous high humidity : The relative humidity of the environment is at a high level for a long time, but the temperature is stable and there is no condensation. In this case, the filter material and colloid are in a hygroscopic state, but if no liquid water is formed, the impact is relatively controllable. What needs to be paid attention to is the performance changes of the material after long-term moisture absorption - whether the resistance drifts, whether the colloid softens, and whether the outer frame corrodes.

Short-term condensation : When the temperature fluctuates or the equipment starts and stops, the surface temperature of the filter element is lower than the dew point, and the water condenses into liquid water on the filter material or outer frame. This risk depends on the magnitude, frequency and duration of temperature changes and has little to do with average humidity. A filter element may repeatedly condense due to frequent starts and stops in an environment with low average humidity.

Direct contact with water : Cleaning operations, pipeline leaks, and poor drainage cause water droplets to splash or drip onto the filter element. This kind of situation is beyond the scope of application of conventional ULPA, and protective structures or front water-blocking measures need to be considered.

The three corresponding selection directions are different. If you treat short-term condensation as continuous high humidity, you may not be able to choose the right point; if you treat direct water spray as ordinary high humidity, the life of the filter element will be significantly shortened. Pharmaceutical clean area or equipment end applications such as The EFU equipment-end fan filter unit has frequent starts and stops or a lot of cleaning operations, and the risk of condensation needs to be assessed individually.

Filter materials, colloids, and seals must be checked separately.

The moisture resistance of ULPA is not determined by a single material, and several parts have their own boundaries.

Filter material : Glass fiber and PTFE have different hygroscopic properties. PTFE has lower hygroscopicity and may have more advantages in dimensional stability and resistance stability in high-humidity environments. The properties of glass fibers may change when they absorb moisture, depending on fiber surface treatment and actual humidity conditions. When selecting, confirm with the supplier the applicable data of the filter material under the target temperature and humidity. involving When selecting the ULPA ultra-high efficiency filter , the material confirmation should cover the entire configuration.

Edge sealing glue : The colloid may age, soften or reduce its bonding strength if it is exposed to a high humidity environment for a long time. This kind of problem may not appear immediately during routine leak detection, but will be exposed after running for a period of time. For specific colloid selection methods, please refer to the relevant instructions on selecting sealants according to working conditions.

Sealing gasket : The resilience performance may change after moisture absorption, which affects the sealing effect after compression. If the gasket has been used for a long time, it is recommended to evaluate it when replacing the filter element.

Outer frame : Whether the anti-rust treatment of the metal outer frame meets the humidity requirements. Aluminum alloy and stainless steel perform differently in high-humidity environments. For specific material selection, please refer to the instructions related to the comparison of outer frame materials. If the outer frame rusts or deforms in a high-humidity environment, the contact state of the sealing surface will be affected.

Incorporate resistance changes into monitoring

Dampness of the filter material may cause abnormal resistance, and comparable operating records need to be established on site.

Initial baselines are recorded. After installation, measure the air volume and pressure difference under stable conditions as a starting point for subsequent comparisons. The resistance change trend in a high-humidity environment is different from that in a dry environment. Abnormalities cannot be judged without a benchmark.

Measure differential pressure and air volume regularly. If you find that the pressure difference rises too quickly, or the air volume drops significantly at the same gear, you need to evaluate whether the filter material is damp or whether there is a problem with the front stage. For specific troubleshooting ideas, please refer to the relevant instructions on increased pressure difference.

Don’t just look at the appearance after getting wet. Just because the filter element is dry on the outside does not mean there are no problems with the internal pleats and glue lines. If there has been an obvious condensation or water contact incident, even if the appearance returns to normal, it is recommended to re-inspect according to the project requirements instead of continuing to use it directly. Supporting For FFU fan filter unit systems, if there is a risk of condensation inside the unit, the status of the filter element must also be checked.

What should you pay attention to during operation and maintenance?

In high-humidity environments, operating methods and maintenance rhythms also need to be adjusted.

Avoid frequent starts and stops. If the equipment is allowed to operate continuously, reducing the number of starts and stops can reduce the risk of condensation. If startup and shutdown are necessary, the system humidity can be reduced before shutdown or the stabilization time after startup can be extended.

Drainage and dehumidification should be in place. If the front-stage dehumidification and drainage measures are taken, the risk of moisture in the terminal filter element will be significantly reduced. For specific front-end configuration, please refer to the instructions related to pre-filtering.

The replacement operation should avoid periods of high humidity. If the ambient humidity is controllable, try to replace the filter element during a period of lower humidity to reduce the chance of the filter material being exposed to moisture during disassembly and assembly.

Pay attention to the storage of spare parts. Uninstalled filter elements should be kept in their original packaging and stored in a dry area. The original packaging still has a protective effect during storage and is not recommended to be removed in advance.

Project judgment example

A certain pharmaceutical clean area uses ULPA filters. The relative humidity of the environment is around 70% for a long time, and the equipment starts and stops twice a day.

After half a year of operation, the pressure difference of some filter elements increased significantly faster than expected. On-site leak inspection found that there were slight abnormalities in the location of some glue seams. After disassembly and inspection, it was found that there were traces of moisture on the edges of the filter material, and the colloid was partially softened.

The investigation found that the temperature dropped after the equipment was shut down, the surface of the filter element was lower than the dew point, and short-term condensation occurred every time it was started and stopped. Although the average humidity is not extreme, frequent condensation events cumulatively affect the colloidal state.

Treatment direction: Adjust the equipment start-up and stop procedures to reduce the system humidity before shutting down; replace with a colloid solution with better moisture resistance performance; increase the frequency of pressure difference monitoring during operation, and handle any abnormalities in a timely manner. involving The logic is the same when selecting HEPA/ULPA air filters .

The key point in this case is this: average humidity is not the only indicator, the frequency and duration of condensation events are equally important.

Selection and Acceptance Checklist

About Aili Industrial’s supporting equipment for high humidity conditions

The prerequisite for ULPA selection in high-humidity environments is to understand the humidity, temperature fluctuations, condensation risks and material applicable conditions. The more complete this information is, the more targeted the plan will be.

Aili Industry has independent manufacturing capabilities in filters, fans, control systems and sheet metal processing, and can provide ULPA ultra high efficiency filter、HEPA high-efficiency filter and supporting air supply equipment. For projects under high-humidity conditions, we can assist in checking the filter material type, colloid scheme and outer frame treatment method based on the continuous temperature and humidity range, temperature fluctuation range, and whether there is a risk of condensation or water dripping. When the filter is matched with equipment such as FFU and EFU, the overall machine protection measures and operation strategies can also be evaluated together during the planning stage.

When enquiring, provide the temperature and humidity data of the usage environment, operating mode and cleaning method, which will help confirm the appropriate configuration for high-humidity conditions. The specific selection is subject to the technical documents and operating data confirmed by the project.