How to convert the clean area area into air supply demand?

The area of ​​the clean area is one of the inputs for estimating the air supply volume, but it cannot alone determine the air supply volume. For an area of ​​the same area, whether unidirectional flow or non-unidirectional flow is used, the air supply demand varies greatly; pollution load, heat and moisture load, exhaust conditions and air flow organization will also affect the final air volume.

Simply multiplying the area by a fixed number makes it easy to overestimate or underestimate equipment needs. The following will start with the airflow form, calculation caliber, working point check, and system balance.

First distinguish between unidirectional flow and non-unidirectional flow

The first step in calculating the air supply volume is to determine which airflow pattern the area uses:

• Unidirectional flow area : air passes through the work area in a stable direction and at a uniform speed, usually estimated by the effective air supply area and the target average wind speed;

• Non-unidirectional flow area : air is mainly diluted and mixed, usually calculated based on room volume and ventilation requirements.

The two forms have different calculation calibers, and areas or arbitrary sets of fixed values ​​cannot be mixed. If you are still unclear about the options at the program level, you can see How to choose between whole room purification and local purification ? First confirm the air flow pattern, and then enter the air volume calculation.

Unidirectional flow area: wind speed times effective area

The air supply volume in the one-way flow area can be estimated by multiplying the target average wind speed by the effective air supply area. Please note when calculating:

• The area should be the effective air supply area, not the floor area of ​​the room;

• The wind speed should be the average wind speed on the cross-section of the working area, not a single point reading on the wind outlet surface;

• Wind speed and area should come from the same section.

For the conversion method of face wind speed and air volume, please refer to How to convert face wind speed and air volume? , the judgment of the effective air outlet area can be referred to How should we look at the effective air outlet area of ​​FFU?。

If the area diameter is used incorrectly, different average wind speeds will be calculated for the same air volume, which will affect the judgment of the number of equipment.

Non-unidirectional flow areas: volume and air exchange requirements

In non-unidirectional flow areas, the room volume is usually multiplied by the number of air changes to initially calculate the air supply volume. Please note when calculating:

• Volume should use actual controlled space, not floor area;

• The number of air changes should be confirmed according to the process, cleanliness level and pollution load, and cannot be a fixed value;

• When there is a need for continuous exhaust or supplementary air, separate accounting is required.

The number of air changes is only a preliminary calculation, and ultimately the pollution load, heat and air flow organization must be checked. For details, please refer to How to reduce local retention in non-unidirectional flow clean rooms?。

Pollution load and heat and humidity conditions affect air volume

In addition to area and volume, air supply volume should also consider:

• Number of personnel and intensity of activities;

• Equipment produces dust and heat;

• Material unpacking and process emissions;

• Exhaust air volume and make-up air requirements;

• Temperature and humidity control requirements.

These factors will affect the actual required air volume. If you estimate based on area only, you may ignore the additional demands caused by continuous exhaust or high heat loads.

The initial calculation of air volume should return to the on-site conditions.

The initially calculated air volume needs to be checked with the system resistance, fan operating point and filter configuration. Continuous exhaust drafts, inlet resistance, equipment occlusion and personnel movement can alter the effective air supply.

When selecting FFU or fan box, you should check the working point including the filter and air path resistance, leaving reasonable adjustment conditions. The complete performance curve is available for reference Why should we look at the complete performance curve when selecting FFU? , the external static pressure can be referred to What does FFU external static pressure mean?。

Connection with air supply coverage and number of equipment

After the air supply volume is determined, the number of equipment 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. For details, please refer to How does clean air supply coverage affect the number of equipment?。

When estimating the number of equipment, the effective air outlet area should be used instead of the box external area. If there is already insufficient air volume at the site, please refer to What are the on-site manifestations of insufficient FFU quantity? Check.

The balance between return air and supplementary air

The air supply volume should not only look at the supply side, but also check the return air and make-up air. If the return air channel is blocked or the air supply is insufficient, the actual air supply volume will not reach the design value.

If the project involves continuous exhaust, the balance between make-up air and exhaust air should be checked to avoid loss of room pressure differential. This is especially important when modular expansion, please refer to What are the expansion conditions for using independent modules in clean systems?。

Equipment selection and terminal matching

Please refer to the room background air supply FFU clean air supply products , please refer to the local protection of the equipment side. EFU equipment side fan filter unit . The logic of division of labor between the two lies in The division of labor between device-side EFU and room FFU is explained in detail.

Filter selection should correspond to target particle size and actual resistance.The HEPA and ULPA filter pages have parameters for different levels of products. When selecting, check the efficiency of the specific model at the target air volume. If you are still unclear about the difference between space rating and filter efficiency, you can read What is the difference between cleanliness level and filtration efficiency?。

If multiple devices require partition duty and troubleshooting, they can be combined FFU group control system provides unified management.

Project judgment example

In a certain project, the air supply volume was estimated based on the room area multiplied by a fixed number of air changes. After installation, it was found that the air speed at the workstation was insufficient. The investigation found that there was continuous exhaust air in the room, the air supply volume was insufficient, 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 area conversion air supply demand must be comprehensively judged based on the air flow form, effective area, pollution load and system balance.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

The calculation of air supply demand ultimately comes down to equipment configuration. Aili Industrial has collaborative capabilities in fans, motors, filters, control systems and complete machine assembly. It can check the target air volume, filter resistance and fan working point based on the project air flow form, effective air supply area and pollution load, helping to convert area estimates into executable equipment quantities and control plans. Specific models can be viewed FFU clean air supply products , supporting equipment can be viewed EFU equipment end fan filter unit , please refer to the filter package. HEPA and ULPA filters。