What is the difference between chemical filters and HEPA filters?

When comparing these two filters side by side, many people will look at the efficiency numbers first. But these two numbers don't mean the same thing at all.

The efficiency of HEPA describes the ability to intercept particles of a specific size. The efficiency of a chemical filter describes its ability to remove target gases. No matter how high a value is, it cannot be used to prove another function. Both serve different pollution forms, and have different evaluation standards, detection methods and application scenarios.

Particle capture and gas treatment are two lines

This is the most fundamental difference.

HEPA deals with solid or liquid particles suspended in the air. Its working mechanism is interception, inertial collision and diffusion, and the particles are intercepted by fiber or membrane media. The particle size, concentration and air flow speed of the particles determine the filtration performance.

Chemical filters deal with gaseous pollutants that exist in molecular form. Its working mechanism is adsorption or chemical reaction, and the target gas is removed from the gas flow by an adapted medium. The gas type, inlet concentration, temperature and humidity conditions determine the treatment effect.

The efficiency data on a HEPA report cannot describe the product's ability to treat acid gas, ammonia, or VOCs. Likewise, gas removal data for chemical filters does not represent a certain level of particle filtration. The two evaluation systems do not overlap.

Consider system order when configuring

If a project requires the control of both particulate and gaseous pollution, it is usually necessary to combine the two types of filtration sections. At this time, the order and coordination become important.

A common practice is to add pre-particle protection plus a chemical filtration section plus terminal high-efficiency filtration. The pre-particle filtration can block dust first and reduce the dust coverage of chemical media; the chemical filtration section processes the target gas; the end HEPA or ULPA is responsible for the final particle control. This order is not fixed and must be confirmed based on the dust load, risk of medium powder loss, and system resistance.

Media dust loss needs attention. Some chemical filter materials may produce small amounts of dust during operation. If the chemical filter section is installed after the terminal HEPA, this part of the dust may directly enter the clean side, and it needs to be evaluated whether a protective section needs to be installed behind it. For specific configuration methods, please refer to the chemical filter product range . Description of

Resistance stacking must be calculated together. Adding a chemical filtration section will increase the total system resistance. When selecting a fan, it is necessary to add up the initial resistance and final resistance of filters at all levels to check whether the working point is acceptable. Supporting For FFU systems equipped with chemical filters , the air volume output of the unit after adding a filter section must also be confirmed.

Maintenance cycles are out of sync. The replacement of HEPA is based on the pressure difference and leak detection results; the replacement of the chemical filter is based on the consumption of gas processing capacity, and there may be no obvious change in pressure difference. The maintenance rhythms of the two are different, and the ledgers must be recorded separately.

Acceptance should also be divided into two lines

When accepting the combined system, the two types of indicators must be confirmed separately.

Particle side : HEPA or ULPA efficiency rating, installation sealing, on-site leak detection. The detection methods and judgment standards are implemented according to the corresponding levels. Can be referenced HEPA high-efficiency filters . Testing requirements for

Gas side : Inlet concentration, outlet concentration, removal efficiency or penetration of target pollutants. The detection method should be suitable for the concentration level of the target gas, and the sampling points should be representative of the actual gas flow.

It is impossible to evaluate whether the task of the chemical filtration section has been completed by only performing particle detection. Conversely, just measuring gas concentration cannot prove that particle filtration meets standards. The two records are archived separately, so that when a problem occurs, you can quickly locate which layer the problem is.

cannot replace each other

This principle is particularly important when selecting and modifying.

Increasing the HEPA rating will not solve the gas problem. If there is gaseous pollution in the room or equipment, replacing H13 with H14 may improve particle control, but the gas concentration will not decrease.

Adding a chemical filtration section also does not reduce particle requirements. Chemical media mainly deal with gases and have limited ability to intercept particles. If the project has clear requirements for particle cleanliness, the HEPA or ULPA layer cannot be omitted.

The same appearance does not mean the same function. Some chemical filters are similar in size to HEPA and can even fit into the same frame. However, their media, structure, and detection basis are all different, and their performance after installation is completely different. Before replacement, you need to confirm what functions the system requires. Don't just look at the size match.

Involving device-side applications such as MAU box-type chemical filter or FFU matching solution, the interface and sequence of the two types of filter sections need to be confirmed together in the planning stage.

Project judgment example

A certain equipment requires both clean air supply and organic vapor control.

The preliminary plan is only equipped with HEPA, thinking that high-level filtration can solve two problems at the same time. After operation, it was found that the particle indicators were normal, but there was still a solvent smell inside the equipment, and some sensitive components were abnormal.

Investigation confirmed: HEPA has no ability to treat organic vapors, and the odor and component abnormalities are related to gaseous pollution. The adjustment plan is to add a chemical filtration section suitable for organic gases on the air supply path, while retaining HEPA for particle control. After the resistance, interfaces and maintenance methods of the two-stage filters were rechecked, the system operation returned to normal.

This case shows that particles and gases are two types of problems and require two sets of solutions. You cannot use the efficiency of one filter to infer the functionality of another.

What to know when selecting

If the project requires the control of both particulate and gaseous pollution, it is recommended to state separately in the technical document:

Particle requirements : grade, applicable standards, rated air volume, detection method.

Gas requirements : target pollutant type, inlet concentration range, outlet target, detection method.

System conditions : installation sequence of two-stage filters, total resistance, fan margin, and maintenance space.

Acceptance method : What methods and criteria are used for the particle side and the gas side respectively.

Only when this information is complete can the supplier provide targeted solutions and have a clear basis for acceptance.

Key points for selection and acceptance inspection

About Aili Industrial’s filtration package

The core of the combined configuration of particle filtration and gas phase filtration is to separately confirm the two types of requirements and then check them uniformly at the system level.

Aili Industrial has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing, and can provide HEPA/ULPA filter and chemical filter product series. For projects involving both particle and gas control, the sequence, resistance, and interfaces of the two-stage filters can be checked together during the planning stage to reduce rework caused by configuration mismatch after installation.

Related products:Chemical filter product series、FFU comes with chemical filter . A separate list of particle control targets and gas targets is provided during the inquiry to help confirm the appropriate combination solution. The specific configuration is subject to the technical documents and test results confirmed by the project.