How to determine the clean air supply volume based on actual working conditions?

The determination of clean air supply volume is the core link in selection and design. Many projects will directly ask 'how much air volume is required per square meter', but the supply air volume is not a fixed ratio, but is determined by the actual working conditions. For the same area, different processes, different air flow forms, and different exhaust conditions, the required air volume may vary greatly.

To determine the air volume, you need to first clarify what tasks the air needs to complete, then calculate the system resistance and operating conditions, and finally confirm it through on-site verification. The following will start from the aspects of protection tasks, air flow patterns, particle load, exhaust conditions and heat and moisture load.

First, clarify what tasks the air needs to complete

Different workstations have different air requirements. Some require one-way protection to allow clean air to cover the product stably; some focus on dilution and elimination of particles; and some require compensation for continuous exhaust.

Different tasks require different calculation methods of air volume:

• One-way protection: estimated based on target wind speed and effective air supply area;

• Dilution and exclusion: initial calculation based on room volume and ventilation requirements;

• Compensated exhaust air: Calculated based on the balance between exhaust air volume and supplementary air.

The same air volume indicator cannot be applied to different tasks uniformly. For the selection logic of airflow form, please refer to How to choose between whole room purification and partial purification ? First confirm the plan level.

The airflow pattern determines the calculation diameter

The calculation calibers for unidirectional flow and non-unidirectional flow are different:

• The one-way flow area is usually estimated by using the effective air supply area and the target average wind speed;

• Non-unidirectional flow areas are usually initially calculated based on room volume and air exchange requirements.

When the wind speed is multiplied by the area, the area should be the effective air supply area; when calculated based on the number of air changes, the volume should be the actual controlled space. The two estimates answer different questions and cannot be mixed. For specific methods, please refer to How to convert the clean area area into air supply demand? and How to convert face wind speed and air volume?。

Particle load affects air volume requirements

Particle loads come from people, materials, equipment and processes. The larger the load, the higher the dilution or removal capacity required.

Should be recorded:

• Number of personnel and intensity of activities;

• Equipment dust production and heat generation;

• frequency of material unpacking and transfer;

• Particle generation during the process.

Estimating based on area alone may ignore the additional demand brought about by continued dust production. To distinguish the sources of pollution, please refer to How to distinguish external and internal contamination when particles exceed the standard?。

Exhaust air and supplementary air conditions

If the area has continuous exhaust air, the air supply volume needs to compensate for the exhaust air to maintain the pressure difference and air flow direction.

Need to confirm:

• Process exhaust volume and changing rules;

• The need for local exhaust hoods;

• Source and path of supplementary wind;

• Room pressure difference requirements.

Imbalance between exhaust air and supplementary air will cause air flow path changes or pressure difference fluctuations. Related calculations can be found in How to convert the clean area area into air supply demand? , understand the air volume balancing method.

Heat and moisture load also affects air volume

Equipment heat, personnel heat dissipation and lighting heat will affect the room temperature. Air conditioning systems need to handle heat and moisture loads, which can affect air supply volume.

When judging, you should confirm:

• heat generation of equipment and lighting;

• Personnel heat dissipation;

• Temperature and humidity control requirements;

• The relationship between air conditioning air supply and clean air supply.

Heat and moisture loading and particle control may be handled by different systems, but the two need to be coordinated. For verification of specific working conditions, please refer to What should be checked if particles increase after the air conditioner is turned on?。

The initial calculation of air volume should return to the system resistance

The initially calculated air volume needs to be checked with the system resistance and fan operating point. Filters, ducts, return ducts, and connecting parts all create resistance.

When selecting equipment, you should check the working point including the filter and air path resistance, leaving a reasonable adjustment margin. For the method of determining the working point, please refer to Why should we look at the complete performance curve when selecting FFU? , the influence of static pressure outside the machine can be referred to What does FFU external static pressure mean?。

From actual working conditions to equipment quantity

After the air volume is determined, the number of devices needs to be calculated based on the coverage rate. Coverage affects the effective air outlet area and protection continuity, thereby affecting the number of devices.

When estimating the number of equipment, the effective air outlet area should be used instead of the box external area. Related methods can be found in How does clean air supply coverage affect the number of equipment? and How should we look at the effective air outlet area of ​​FFU?。

On-site verification confirms the air volume effect

The air volume calculation will ultimately fall to on-site verification. Verification content includes:

• Wind speed and airflow direction at key workstations;

• Total air volume and pressure difference;

• Particle concentration and recovery time;

• Protection effectiveness under dynamic conditions.

If increased air volume does not improve protection, the source of contamination and airflow paths should be examined rather than continuing to increase speed. The influence of air supply distance on air flow can be referred to How will the airflow change when the air supply distance increases?。

Project judgment example

For a certain project, the air volume was estimated based on area, but the air speed at the workstation was insufficient after installation. The investigation found that the room had continuous exhaust air, insufficient air supply, and the actual effective air supply was lower than the design value. Adjustment method: Recalculate the balance of exhaust air and supplementary air, and adjust the number of equipment and operation settings according to the actual working point. The wind speed at the workstation recovered after adjustment.

Another project was estimated based on the one-way flow wind speed multiplied by the area, but the area used the floor area of ​​the room instead of the effective air supply area, resulting in an excessive number of equipment. Adjustment method: Recalculate according to the effective air outlet area and actual coverage requirements, and optimize the equipment layout. After adjustment, the number of equipment is reasonable and the wind speed meets the requirements.

These two situations illustrate that the supply air volume must be comprehensively determined based on the protection tasks, airflow patterns, particle loads, exhaust and heat and humidity conditions, and cannot be calculated solely based on area or grade.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

The determination of the supply air volume requires a combination of protection tasks, airflow patterns, particle load and system resistance. Aili Industrial has collaborative capabilities in fans, motors, filters, control systems and complete machine assembly links. It can check the target air volume, filter resistance, fan operating points and equipment quantity based on the actual working conditions of the project, helping to convert air volume requirements into equipment configurations that match the site, rather than just estimating based on area or grade.