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

The pressure difference between the inside and outside of the air conditioning box must be considered for drainage in both the positive pressure section and the negative pressure section of the air conditioning box, but the directions of air flow are different. Positive pressure may push air to leak out, while negative pressure may suck in outside air and affect drainage. The two types of drainage structures should be designed according to the pressure of the respective sections, and different pressure sections cannot be directly connected at will.

First, label each drain outlet with a pressure attribute.

Different water trays in the same unit may be located before and after the fan, and changes in operating mode may also affect local pressure. If multiple outlets are directly connected to the same pipe, there may be mutual air leakage or interference in the discharge through the drainage pipe. The need for separate structures, branching arrangements and appropriate downstream connections should be checked and determined by the drainage design.

For positive pressure branches, leaked air, sealing water maintenance and downstream connections must be checked; for negative pressure branches, the influence of suction, effective drainage and water sealing conditions must be checked; for co-pipeline situations, air leakage, backflow, elevation and pressure differences in each section must be checked. The three types of situations correspond to different drainage risks and cannot be handled uniformly according to 'drainage tray'. Why water sealing is often needed for negative pressure drainage of air conditioning boxes? Please refer toWhy does negative pressure drainage of air conditioning boxes often require water sealing?。

Positive pressure section drainage: prevent air leakage and backflow

The positive pressure section is located on the outlet side of the fan, and the pressure inside the box is higher than the outside pressure. If the drain outlet is not tightly sealed, the treated air may leak out from the drain pipe, causing a loss of air supply volume and an increase in energy consumption. If there is a backflow condition at the outlet of the drain pipe, external water or odor may also enter the box. Drainage in the positive pressure section needs to prevent air leakage and ensure that condensate can be discharged smoothly.

Drainage in the positive pressure section does not necessarily require as high a water seal as in the negative pressure section, but water sealing or non-return measures still need to be set according to the direction of the drainage pipe and outlet conditions. If the drain pipe is directly connected to an open drainage point, it should be confirmed that no air flow short circuit will occur. How to combine the slope of the water pan of the air-conditioning box with the layout of the drain outlet, please refer toHow to combine the slope of the water pan of the air-conditioning box with the layout of the drain outlet?。

Negative pressure section drainage: prevent air suction and drainage from being blocked

The negative pressure section is located on the suction side of the fan, and the pressure inside the box is lower than the outside. If the drain outlet is directly opened, outside air will be sucked into the box from the drain pipe, hindering the discharge of condensed water, and even water accumulation or backflow in the drain pipe may occur. Drainage in the negative pressure section usually requires a water seal or other drainage structure confirmed by design, and the height of the water seal should be calculated based on the actual negative pressure.

When the water seal height in the negative pressure section is insufficient, air may break through the water seal; when the water seal is too high, drainage resistance increases. The water seal also needs to be replenishable, inspectable, and clearable. It may fail due to evaporation or siphoning after a long shutdown. How to prevent external air leakage when a chemical filter is installed in the negative pressure section, please refer toHow to prevent external air leakage when a chemical filter is installed in the negative pressure section?。

Different pressure sections should not share the same drain outlet at will.

If the water trays of the positive pressure section and the negative pressure section share a drainage pipe, air leakage may occur through the drainage pipe. The negative pressure section may suck air from the drainage outlet of the positive pressure section, and the positive pressure section may leak air into the drainage pipe of the negative pressure section, resulting in poor drainage or failure of water sealing. Multiple drainage pans should be equipped with separate drainage branches, or independent water seals and confluence methods should be installed after design confirmation.

There may be multiple pressure zones in the same unit. How the sequence of functional sections is arranged will affect the pressure distribution. Please refer toOn what basis should the sequence of functional sections of the air conditioning box be determined? . The layout of drainage pipes should be checked in conjunction with the box structure and pressure zones, and should not be temporarily taken over after the equipment is in place.

The foundation height and drainage elevation should be checked separately

The water seal height, drain outlet elevation and outer pipe slope may be different between the positive pressure section and the negative pressure section. The water seal in the negative pressure section requires a certain height. If the foundation is too low, it may not be installed. If the drainage outlet in the positive pressure section is too high, the slope of the outer pipe may not be enough. The two types of drainage points should be marked with elevation and direction respectively, and should not be given a uniform basic height.

How to determine the foundation height of horizontal air-conditioning boxes based on drainage conditions, please refer toHow to determine the foundation height of a horizontal air conditioning box based on drainage conditions? . The slope of the water pan and the location of the drain outlet should also be checked together with the foundation height.

Override the actual operating mode when debugging

Not only check the natural drainage after shutdown, but also observe each branch under relevant air volume and pressure conditions. Pipeline clearing and water sealing maintenance should be at accessible locations, and where the water is discharged must also meet on-site design requirements. If there is water accumulation in a certain section, other branches and public pipelines should be checked at the same time to avoid treating only the visible one.

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? . 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? . When drainage is abnormal, you should first check the pressure partition, water seal and pipeline, and then determine the problem of the water tray or coil.

Aili industrial supporting equipment

Aili Industrial can provide drainage interface information according to functional sections. The project party should mark the positive and negative pressures and downstream connections respectively on the connection diagram to facilitate collaborative confirmation of equipment and on-site drainage. 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. Water trays, drain outlets, water seal reservations and box pressure zones can be matched in the same package; non-standard drainage solutions can be adjusted according to on-site pressure conditions and space.

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 drainage plan, water seal height 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 drainage inspection and performance test results.

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

Related questions and answers

Does water sealing also need to be used for drainage in the positive pressure section?
It is not necessarily necessary to have a water seal as high as the negative pressure section, but it is still necessary to prevent air leakage and backflow. Water sealing or non-return measures should be set according to the direction of the drainage pipe and the outlet conditions.

Can the positive pressure section and the negative pressure section share the same drainage pipe?
Not recommended for casual sharing. Gas cross-flow and mutual interference may occur in shared pipes. Branch circuits should be set up separately or independent water seals and confluence methods should be set up after design confirmation.

Can Aili Industrial help check the positive and negative pressure drainage plans?
The interface and water sealing scheme can be checked based on the pressure zone, the location of the water tray and the on-site drainage conditions. The specific configuration needs to be confirmed according to the project conditions.

Related articles

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

2. How to combine the slope of the water pan of the air-conditioning box with the layout of the drain outlet?

3. How to determine the foundation height of a horizontal air conditioning box based on drainage conditions?

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

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