How is the total pressure of the air conditioning box fan determined by the internal resistance and external demand?

The air-conditioning box fan pressure budget should be within the agreed calculation boundary, connecting the loss in the processing section of the machine with the pressure required by the external air path, and then checking it according to the full pressure or static pressure performance caliber adopted by the fan. The external static pressure figure cannot be directly regarded as the fan's full pressure requirement without explanation.

First establish a pressure account of the same caliber

List the filter usage status, coil working condition, internal accessories and external pipe network separately. The designer provides external requirements, and the manufacturer explains the internal configuration and boundary processing. The fan performance curve should correspond to the target flow rate and avoid taking the zero air volume pressure or the maximum air volume point to meet the two requirements respectively.

The design flow rate must make it clear that all pressure loss data use the same representative air volume; the internal losses must correspond to the actual functional sections and filter status; external requirements must indicate whether air ducts, valves, and terminal equipment are included. Only when the three items are placed in the same table can the pressure budget have closing conditions. What functional segments does the internal resistance include? Please refer toWhat functional segments should be included in the internal resistance of the air conditioning box?。

The internal resistance of the machine should be calculated according to the actual function section

Internal resistance includes filters, coils, humidification or water retaining devices, muffler structures, internal air valves and transition air ducts. The filter must distinguish the initial resistance and the final resistance, the coil must confirm the dry and wet working conditions and the actual air volume, and the local resistance of the muffler and damper must not be omitted. The list must be consistent with the selected configuration, and uninstalled functional segments cannot be included in the sample.

How to configure filter classification, please refer toHow to configure the primary-efficiency and medium-efficiency filters of air-conditioning boxes in different stages? . How to select the type of surface cooler according to the air inlet and outlet conditions, please refer toHow to select the type of air conditioner cooler according to the air inlet and outlet conditions? . How to determine the order of function segments, please refer toOn what basis should the sequence of functional sections of the air conditioning box be determined?。

Off-machine requirements must be clearly defined with boundaries and attachments

External requirements include the resistance of air ducts, valves, terminal equipment, mufflers and air supply ports. But where to start counting 'off-camera' depends on the technical agreement. Which end filter, outlet silencer section or high-efficiency air supply port is included in the external resistance of the unit, and which is internal to the unit? Different projects may have different agreements.

Please refer to the caliber differences between external static pressure, full pressure and static pressure.What is the difference between static pressure, total pressure and static pressure outside the air conditioner box? . Whether the high-efficiency filter is placed inside the machine or at the end will affect the pressure boundary. Please refer toShould the high-efficiency filter of the air-conditioning box be placed inside the machine or at the end of the air supply? . When making an inquiry, the interface location, design air volume and accessories range should be clearly stated one by one. Please refer toHow to write an inquiry form for air-conditioning boxes so that different quotes can be compared?。

The fan curve should correspond to the target air volume

Fan performance curves usually give the relationship between total pressure or static pressure as a function of air volume. After the pressure budget is determined, it should be checked whether the fan can provide the required pressure under the target air volume, and whether the working point falls within the stable operating range and efficiency range. You cannot use the zero air volume maximum pressure or the maximum air volume point to meet the two requirements respectively.

How to check the fan efficiency range, please refer toWhy should we check the efficiency range when selecting air-conditioning box fans? . For comparison between backward-inclined and forward-inclined fans, please refer toHow do the backward-inclined and forward-inclined fans compare when used in air conditioning boxes? . For DC fan drive matching, please refer toWhat driving conditions need to be matched when using a DC fan in an air-conditioning box?。

If there is a margin, avoid repeated overlays.

If the final resistance of the filter, external margin and fan selection margin are repeatedly superimposed, it may lead to an oversized installation, debugging throttling and increased noise. The purpose of each margin should be explained, common working conditions and adjustment intervals should be reviewed, and finally the fan, motor and driving capabilities should be confirmed. The margin should be based on specific uncertainties rather than adding a general coefficient.

When the air volume is insufficient, check the measurement first or increase the speed first. Please refer toIf the total air volume of the air conditioning box is insufficient, should I check and measure it first or should I increase the speed first? . How to estimate annual energy consumption, please refer toWhy can’t the annual energy consumption of air conditioning boxes be estimated based on rated power alone? . The relationship between pressure margin and operating energy consumption should be explained at the planning stage.

On-site measurements should correspond to the design diameter

When measuring pressure on site, the location of the measuring point, pressure measurement method, air volume and air condition should be recorded. The static pressure measured at different locations of the same unit may be different, and the outlet dynamic pressure will also affect the total pressure reading. When comparing the design value and the actual measured value, first confirm whether they use the same caliber.

For condition checks before starting the machine for the first time, please refer toWhat conditions need to be checked before the air-conditioning box 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? . The on-site acceptance record should be able to correspond to the design pressure caliber and test conditions.

Aili industrial supporting equipment

Aili Industrial can check the fan, motor and filter configuration at the same working point; it is recommended to attach a sub-item resistance table to facilitate confirmation of the pressure budget and subsequent test boundaries. 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 internal resistance, external requirements and fan working points can be aligned in the same package; non-standard configurations can be adjusted according to project resistance conditions.

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; multiple equipment linkage can understandMatching method of FFU computer group control system ; terminal particle filtering can be combinedHEPA/ULPA filter confirmation; when it comes to gaseous pollution control, you can communicate separatelyChemical filter solutions. The specific pressure budget, fan performance and delivery scope still need to be verified based on the corresponding configuration data and on-site working conditions. The actual effect is subject to the on-site air volume balance and pressure measurement results.

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Related questions and answers

Can the external static pressure be directly used as the fan full pressure requirement?
cannot. The static pressure outside the machine and the full pressure caliber of the fan are different, and the influence of internal resistance and dynamic pressure needs to be calculated and checked according to the same caliber.

Is the larger the fan pressure margin, the better?
no. Excessive margin will lead to larger installed capacity, debugging throttling, and increased noise. Reasonable margins should be set for specific uncertain items.

Can Aili Industries help establish a stress budget?
The fan working point can be checked based on the itemized resistance table and target air volume. The specific budget needs to be confirmed based on the project configuration and system conditions.

Related articles

1. What functional segments should be included in the internal resistance of the air conditioning box?

2. What is the difference between static pressure, total pressure and static pressure outside the air conditioner box?

3. Why should we check the efficiency range when selecting air-conditioning box fans?

4. If the total air volume of the air conditioning box is insufficient, should I check and measure it first or should I increase the speed first?

Key points for selection and acceptance inspection