What is the difference between positive pressure air leakage and negative pressure suction air leakage in air conditioning boxes?

Air leakage in the positive pressure area of ​​the air conditioning box usually means that the treated air escapes outwards, while air leakage in the negative pressure area may inhale unfiltered air from the surrounding area. Both lose system control capabilities, but have different impacts on cleanliness, energy consumption and pollution paths. They should be analyzed based on the position of each functional section relative to the fan.

Mark pressure zones along the front and rear of the fan

There may be both a negative pressure section and a positive pressure section in the same air conditioning box. When the air in the computer room enters through the gap in the negative pressure inspection door, it may bypass the previous treatment; leakage in the positive pressure section may reduce the air volume available to the end. If the unit is located in a dirty or humid environment, the consequences of negative pressure suction need to be evaluated in conjunction with downstream filtration tasks.

In the positive pressure area, the effective air supply loss caused by door gaps, seams and leakage must be checked; in the negative pressure area, the suction path of untreated air and the surrounding environment must be checked; at the pressure conversion point, the partition must be confirmed based on the actual fan position, resistance and operating mode. The three types of positions correspond to different sealing points, so you cannot just check the filter element frame. Under what pressure conditions should the air leakage rate of air conditioning boxes be compared? Please refer toUnder what pressure conditions should the air leakage rate of air conditioning boxes be compared?。

Positive pressure air leakage is the escape of internal air to the outside

The positive pressure section is located on the outlet side of the fan, and the pressure inside the box is higher than the surrounding environment. Once there are gaps in the box, the treated air will leak out. If the leakage point is after the filter section, treated air will leak out, and the main impact will be loss of air supply volume and increased energy consumption; if the leakage point is before the filter section, untreated air will leak out, which may contaminate the surrounding area of ​​the equipment or adjacent areas.

Positive pressure air leakage is usually easier to observe on the outside of the joint with a smoke or anemometer. During inspection, you should confirm whether the leakage point is located in front or behind the filter section, because the impact of the two is different. For the difference between positive pressure section drainage and negative pressure section drainage, please refer toWhat is the difference between the positive pressure section drainage and the negative pressure section drainage of the air conditioning box?。

Negative pressure suction means outside air is sucked in

The negative pressure section is located on the suction side of the fan, and the pressure inside the box is lower than the surrounding environment. Once there are gaps in the box, outside air is sucked into the box. The inhaled air may not be filtered. If the leakage point is located downstream of the filter section, it will directly affect the air supply cleanliness or gas control effect. Leakage points of negative pressure suction are often more hidden, because the outside air looks clean, but the composition may not meet the process requirements.

For prevention and control of external air leakage in the negative pressure section, please refer toHow to prevent external air leakage when a chemical filter is installed in the negative pressure section? . Drainage in the negative pressure section also requires water sealing, please refer toWhy does negative pressure drainage of air conditioning boxes often require water sealing?。

The two types of air leakage have different impacts on the system

Positive pressure air leakage mainly causes loss of air supply volume, increased fan energy consumption and possible external pollution; negative pressure suction mainly causes untreated air mixing, filter bypass and downstream cleanliness or gas control failure. Positive pressure air leakage may appear as airflow or noise outside the unit, while negative pressure suction may not be easily noticeable outside, but outlet inspection or cleanliness testing will reflect the problem.

When the total air volume is insufficient, you can refer toIf the total air volume of the air conditioning box is insufficient, should you check and measure it first or increase the speed first? . Filter bypass and sealing issues, please refer toHow to configure the primary-efficiency and medium-efficiency filters of air-conditioning boxes in different stages?。

Seal inspection should be carried out according to pressure zones

In the positive pressure section, check whether the door seams, flanges, splicing seams and air duct interfaces are leaking to the outside; in the negative pressure section, check whether the door seams, flanges, splicing seams and access doors are sucking in external air. The leak detection method should be suitable for the pressure direction. For positive pressure, smoke or anemometer scanning can be used, and for negative pressure, gas detection at the joints or shutdown to maintain pressure can be used. Inspections should be carried out under normal operating differential pressure, not shutdown conditions.

The aging of the inspection door seal, the deformation of the door frame and the looseness of the pressing lock are common air leakage points in the positive and negative pressure sections. For general principles of sealing edge protection, please refer toHow to avoid damaging the sealing edge when installing a chemical filter?。

After correction, review in running state

After the seal correction is completed, it should be reviewed under normal operating air volume and pressure difference. The position that does not leak under static conditions may cause gaps due to changes in the force on the box after the fan is running. The review includes whether the pressure difference before and after the filter section is stable, whether the gas after mixing or at the outlet returns to the expected level, and whether there is any abnormal air flow sound around the access door and flange.

How to change the debugging sequence from stand-alone to system linkage, please refer toHow to change the debugging sequence of air conditioning box from stand-alone unit to system linkage? . For condition checks before starting the machine for the first time, please refer toWhat conditions need to be checked before the air conditioner is turned on for the first time?。

Aili industrial supporting equipment

Aili Industrial can check the box, door frame and filter installation structure according to the segmented pressure conditions. The positive and negative pressure directions marked on the technical diagram will help determine the key sealing positions. Aili's industrial manufacturing end covers independent R&D and production of motors and fans, control systems, sheet metal, air filters and complete machine assembly. The box structure, access door seals and pressure zones can be matched in the same package; non-standard boxes can be adjusted according to on-site pressure conditions and maintenance requirements.

Product form can be viewedAir handling unit andFan box page; clean air supply package can be combinedFFU fan filter unit andEFU equipment end fan filter unit verification; terminal particle filtration can be combinedHEPA/ULPA filter confirmation; when it comes to gaseous pollution control, you can communicate separatelyChemical filter solutions. The specific air leakage performance, sealing scheme and delivery scope still need to be verified based on the corresponding configuration data and on-site working conditions. Actual results are subject to on-site leak detection and performance test results.

Submit project parameters:https://ailigy.com/contactus.html

Related questions and answers

Which has greater impact, positive pressure air leakage or negative pressure suction air leakage?
Depend on the location of the leak and the composition of the air. Positive pressure air leakage may result in loss of air supply volume or contamination of surrounding areas, and negative pressure suction may allow untreated air to mix into the downstream. Both need to be evaluated based on the actual path.

Why is it not easy to find air leakage in the negative pressure section?
When the outside air is sucked in, the outside looks clean, but the composition may not meet the process requirements, and the leakage points are often at door gaps or seams, which is not as intuitive as positive pressure leakage.

Can Aili Industrial help check the sealing of the positive and negative pressure sections?
The key points of sealing can be checked based on the box structure, pressure zone and access door form. The specific plan needs to be confirmed based on equipment data and site conditions.

Related articles

1. Under what pressure conditions should the air leakage rate of air conditioning boxes be compared?

2. How to prevent external air leakage when a chemical filter is installed in the negative pressure section?

3. What is the difference between the positive pressure section drainage and the negative pressure section drainage of the air conditioning box?

4. Why does negative pressure drainage of air conditioning boxes often require water sealing?

Key points for selection and acceptance inspection