How to design ultra-thin ULPA when space is limited?

In equipment-side projects, the space left for filters is often determined during the mechanical design stage. Sometimes it's just over 100 mm, sometimes it's not even 100 mm. To stuff ULPA into this kind of space and ensure air volume, efficiency and sealing, it's not as simple as 'choose a thinner filter element.'

The core contradiction of ultra-thin design is that thickness, filter area and resistance are mutually constraining. If it is made thinner, the filtration area will be reduced, and the wind speed will increase and the resistance will increase. To maintain the air volume, a larger area may be needed, but space does not allow it. The balance point in the middle needs to be determined during the planning stage, rather than being adjusted after the prototype is installed. For specific structural features, please refer to the relevant instructions for the structure without partitions.

First confirm how much available space is

Many projects say 'not enough space' but fail to quantify the constraints. Before designing an ultra-thin solution, make sure a few things are clear.

Total height limit. What is the maximum height that the equipment allows the filter element to occupy? Is this value the height of the filter element frame, or does it include installation clearance and maintenance space? The two should be looked at separately.

Installation depth and width. In addition to height, length and width restrictions must also be confirmed. Although some equipment is highly tight, there is margin in the length direction. You can consider increasing the length and width and reducing the thickness to compensate for the area.

Air inlet location and direction. Where the incoming air comes from and where the outgoing air goes will affect the airflow path design inside the filter element. When space is limited, the airflow path may not be straight in and out, requiring the cooperation of a guide structure.

Disassembly and assembly path. After the filter element is installed, can it be taken out? Are there any robotic arms, cables, or structural parts inside the equipment that block replacement access? Some solutions can be installed but cannot be taken out. This problem is not uncommon in device-side projects.

Sealed structural space. The gasket or liquid tank requires a certain amount of compression space. If the thickness has been calculated very tightly, there may not be enough space in the sealing structure, resulting in insufficient compression. For specific sealing methods, please refer to the relevant instructions for liquid tank sealing.

Collate these measurements and make a list of spatial constraints. This list is the basis for subsequent design.

How do area and resistance change after thickness compression?

The most direct impact of reduced thickness is the reduction of filter area.

For the same outer dimensions, a reduction in thickness means a reduction in pleat height or pleat count. If the pleats are highly compressed, the unfolded length of a single pleat becomes shorter; if the number of pleats is reduced, the total unfolded area decreases. Both changes will reduce the effective filter area.

As the area decreases, the passing wind speed increases. Under the same air volume, the smaller the area, the more airflow passes through the filter material per unit area, and the higher the passing wind speed. This will lead to two results: resistance increases and dust accumulation may accelerate.

The rising resistance will affect the fan operating point. If the original fan is selected according to the conventional thickness filter element, after replacing it with an ultra-thin filter element, the system resistance may increase and the air volume may decrease. Supporting FFU fan filter unit or For the fan filter unit system at the EFU equipment end, the fan working point needs to be rechecked.

Therefore, ultra-thin design is not simply about 'making the thickness smaller', but about finding a feasible combination between thickness, area and resistance. Some solutions try to maintain the effective area within a limited thickness by switching to low-resistance filter materials or adjusting the pleated structure; some solutions accept higher resistance and use fans with higher static pressure to compensate. For specific selection methods, please refer to the instructions related to the resistance curve.

How to match filter material and structure

When the thickness is limited, the choice of filter materials and structures will also be narrowed.

Filter media selection. Glass fiber and PTFE have different resistance characteristics at the same thickness. Some low-resistance filter materials can maintain relatively reasonable airflow channels with thinner structures. However, material selection should not only look at resistance, but also check suitability for working conditions. For specific comparison, please refer to the relevant instructions on the selection of glass fiber and PTFE.

Pleated design. When the thickness is reduced, the pleat distance and pleat pattern need to be redesigned. Pleats that are too dense will easily collapse under a thin structure, while pleats that are too sparse will have insufficient area. The pleating parameters should be determined together with the filter material characteristics and air flow conditions.

Glue line layout. The edge sealing glue takes up space, and this part of the space takes up a larger proportion in ultra-thin structures. If the glue line is too wide or unevenly distributed, it may further compress the effective channel. For specific colloid selection, please refer to the relevant instructions on selecting sealants according to working conditions.

Frame stiffness. The ultra-thin frame may be less rigid than regular products. It needs to be evaluated whether the outer frame will be deformed during installation and compression. If the deformation of the outer frame affects the sealing surface, even if the thickness is installed, the sealing may not be up to standard. For specific frame material selection, please refer to the relevant instructions on the comparison between aluminum alloy and stainless steel.

diversion structure. The air inlet and outlet spaces of the ultra-thin filter element are very compact. If the air inlet is too close to the filter element, the airflow distribution may be uneven; if the air outlet side is blocked, the local wind speed may be high. If necessary, it needs to be matched with a deflector or flow sharing structure.

Verification and maintenance cannot be omitted

Due to space constraints in ultra-thin solutions, verification and maintenance are more likely to be ignored.

Filter performance verification. Measure the resistance and efficiency at the target air volume and confirm that they are within the acceptable range. If the on-site air volume and test conditions are consistent, the readings should be within the range corresponding to the curve.

Install leak detection. The sealing surface of ultra-thin filter elements may be narrower, and the installation and compression requirements are higher. After installation, perform on-site leak detection according to the project plan to confirm the effectiveness of the seal. Whether the scan path is reachable needs to be confirmed during the planning stage.

Maintain channel verification. After the filter element is installed, confirm whether the disassembly and assembly operation is feasible. When the internal space of the equipment is tight, it may be necessary to disassemble other parts before replacing the filter element. These operating steps should be confirmed and recorded in advance. For the specific acceptance sequence, please refer to the relevant instructions on whether to adjust the air volume first or check for leaks first.

Run data trace. The resistance of the ultra-thin filter element may be higher than that of conventional products, and the dust accumulation speed may also be different. During operation, the pressure difference and air volume are continuously recorded to determine the actual replacement cycle.

Project judgment example

A certain semiconductor equipment needs to install a ULPA filter inside, and the reserved space at the top of the equipment is only 85 mm. The thickness of conventional ULPA is about 100 mm or more and cannot be installed directly.

The preliminary plan uses ultra-thin ULPA, with a thickness of about 70 mm, and the remaining space is used for sealing structure and installation tolerances. However, the test found that the resistance of the filter element at the target air volume was about 40% higher than the original plan, and the fan operating point was close to the upper limit.

After further calculations, the plan was adjusted: switch to an ultra-thin structure with a larger effective area, and the thickness was increased to 75 mm. However, by optimizing the pleat design, the effective area increased by about 15% compared to the original ultra-thin plan. After adjustment, the resistance is reduced to an acceptable range and the fan operating point returns to the normal range. The internal structure of the device has been slightly adjusted to accommodate the increased thickness of 5 mm.

The key to this case is: ultra-thin design is not simply choosing the thinnest model, but finding a balance between thickness, area, resistance and system capabilities. involving ULPA ultra high efficiency filter or The selection of HEPA high-efficiency filter has the same logic.

Selection and Acceptance Checklist

About Aili Industrial’s ultra-thin solution package

The difficulty in the design of ultra-thin ULPA lies in the mutual constraints of space, area and resistance. If the constraints can be quantified during the planning stage, and then combined with the filter materials and structural options to check them one by one, the probability of finding a feasible combination will be much greater.

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 with limited space, the internal structure of the equipment, available height, target air volume and installation path can be combined to assist in checking the thickness of the filter element, pleat design and sealing scheme. When the filter is matched with equipment such as FFU and EFU, the resistance of the ultra-thin filter element and the working point of the fan can be calculated together at the planning stage to reduce insufficient air volume after installation.

When enquiring, provide the internal structure diagram of the equipment, available space dimensions, target air volume and maintenance requirements to help confirm the appropriate ultra-thin solution. The specific design is subject to the technical documents confirmed by the project and the sample test results.