Whether chemical filters can support partial return air reuse needs to be comprehensively evaluated based on air composition, relevant ventilation requirements and protection objectives. It can only handle target gases that are suitable and have been filtered, and cannot prove that all exhaust air is suitable for reuse. Whether the return air can be used depends on what is in the air first, and then what the filter can handle.

The first hurdle to pass for return air reuse is the ingredients.

Whether return air is suitable for reuse depends first on what components and concentrations are contained in the air. If the return air comes from an area with higher cleanliness, the gas load is mainly low-concentration organic vapor, and the chemical filtration section has the ability to respond to the target components, the risk of partially reused gas control is relatively controllable. If the return air contains high concentrations of process releases, particles, droplets or unknown components, the chemical filtration section alone may not be able to treat it to a reusable level. When evaluating, you should first investigate the composition of the return air, instead of defaulting to 'it can be reused with chemical filtration.'

Filter coverage and reuse ratio restrict each other

The chemical filter only processes the part of the air that passes through it. The higher the reuse ratio, the more obvious the accumulation of unfiltered or insufficiently filtered gas in the system. Partial reuse means that fresh air and return air are mixed, and the mixed gas concentration depends on the return air concentration, return air ratio and filtration effect. If the return air ratio is increased but the filter section capacity or position is not adjusted accordingly, the mixed concentration may exceed the protection requirements. The design of the reuse ratio should be checked together with the air volume, location and media configuration of the filter section. Regarding the impact of the ratio of fresh air to return air on gas control, please refer toIs it feasible to reduce the fresh air volume and combine it with chemical filtration?。

Different gas objects must be judged separately

Particles, gases, humidity and odors in the return air have different control requirements and cannot be summarized by one filter section. The chemical filtration section mainly processes gases and has limited effects on particles and humidity; if the return air particles or humidity do not meet the requirements, particle filtration or dehumidification measures are required. In addition, some gases may not have obvious odors at low concentrations but have an impact on the process. When judging reuse, target gas detection should be the criterion, not the smell. Regarding the division of labor between particle and gas filtration, please refer toThere is a high-efficiency filter in the clean room, why is there still smell?。

Reuse systems need to set monitoring and rollback conditions

Some reuse systems may encounter changes in return air composition, filter section penetration, or working condition adjustments during operation, and monitoring points and fallback conditions need to be set. Monitoring points should cover return air, post-mixed air supply and key protection positions; fallback conditions can include reducing the reuse ratio or switching back to fresh air operation when the outlet concentration exceeds the set value, the pressure difference is abnormal, or the filter section reaches replacement conditions. If the reuse is run as a fixed ratio without monitoring, the risk is that it cannot be adjusted in time after the performance of the filter section changes. Regarding the relationship between return air utilization and energy saving, please refer toCan the chemical filter modification be done together with the energy-saving modification of the air conditioning box?。

Aili industrial supporting equipment

For return air reuse projects, we usually recommend that customers first conduct a survey on the return air composition, and then check whether the gas control is established based on the filter section configuration and reuse ratio, rather than determining the reuse ratio first and then refiltering. Aili Industry can provide selection packages for box-type, flat-plate and V-type chemical filtration products. For box-type MAU packages, please refer toMAU box type chemical filter , product series can be viewedChemical filter product range . The V-shaped structure provides a larger filtration area in the same box space, which helps control surface speed and resistance when the return air ratio is increased. Equipment end or circulation section can useChemical filter FFU type, integrated chemical adsorption layer withHEPA/ULPA filter particle filtration, particles and gases in the return air can be treated separately. The manufacturing end covers independent R&D and production of motors and fans, control systems, sheet metal and complete machine assembly. The return air ratio, filter section position and fan operating point can be checked in the same package, and non-standard air paths can be adjusted according to on-site conditions. The specific gas effect, applicable environment and replacement cycle still need to be verified based on the corresponding configuration data and on-site working conditions. The actual results are subject to on-site leak detection and gas detection results.

Related questions and answers

With a chemical filter, can all the return air be reused?
cannot. Reuse depends on the return air composition, concentration, filter section capacity and protection objectives. High-proportion reuse needs to be checked separately and cannot be established by default.

Can chemical filters handle the particles and humidity in return air?
The chemical filtration section mainly handles gases and has limited effect on particles and humidity. When particle filtration or dehumidification measures are required, they should be configured separately.

Can Aili Industrial help check the return air reuse plan?
It can be combined with the return air composition, filter section configuration and reuse ratio to assist in checking gas control and monitoring arrangements. The specific plan needs to be confirmed based on product data and on-site working conditions.

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• Can the chemical filter modification be done together with the energy-saving modification of the air conditioning box?

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Key points for selection and acceptance inspection