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

Static pressure and total pressure are air flow pressure indicators, and total pressure includes static pressure and dynamic pressure; external static pressure is used to describe the pressure available for external systems under the agreed interface and calculation caliber. When comparing air conditioning box parameters, you should first confirm the measurement points, air volume and pressure definitions. Do not treat the three values ​​as the same item.

The pressure name must correspond to the location and operating conditions

The fan must overcome the losses caused by the unit's internal treatment section and external air path. 'Outside' in the unit selection book usually means outside the unit boundary, but whether it is included in an attachment depends on the technical agreement. Different outlet wind speeds will change the dynamic pressure, and different pressure-taking locations and methods will also affect the actual measured readings.

The static pressure is related to the pressure taking method and location and needs to be compared in the same caliber; the total pressure is the sum of static pressure and dynamic pressure, which is used to correspond to the fan performance curve; the external static pressure must clearly define the delivery interface and the included external resistance range. The three names correspond to different measuring points and calculation methods and cannot be used interchangeably. How to form the internal resistance of the air-conditioning box, please refer toWhat functional segments should be included in the internal resistance of the air conditioning box?。

The relationship between static pressure, dynamic pressure and total pressure

When the air flows in the air duct, there is both static pressure perpendicular to the pipe wall and dynamic pressure generated with the flow rate. Total pressure is equal to the sum of static pressure and dynamic pressure. At the same cross-section, the higher the wind speed, the greater the dynamic pressure, and the relatively lower static pressure. To measure the total pressure, you need a pressure pipe facing the air flow, and to measure the static pressure, you need a pressure pipe perpendicular to the air flow.

Fan samples usually give performance curves in the form of full pressure or static pressure. When comparing, you must confirm which pressure caliber the curve corresponds to. If the full pressure of the fan is directly used as the external static pressure, the pressure available to the external system may be overestimated; if the static pressure is used as the total pressure, the fan capacity may be underestimated. Why should you check the efficiency range when selecting a fan? Please refer toWhy should we check the efficiency range when selecting air-conditioning box fans?。

The boundary of external static pressure must be clearly written

The external static pressure describes the pressure available to the external air duct outside the unit delivery interface. But where exactly this 'external' starts depends on the technical agreement. Which of the terminal filters, air valves, mufflers, air ducts and air supply outlets are included in the external resistance of the unit, and which are internal to the unit, may have different agreements in different projects.

If the unit contains a terminal high-efficiency filter or an outlet silencer section, the starting point of the external static pressure will then move backward. During inquiry and acceptance, the interface location, design air volume, and whether the end filter is included should be clearly stated one by one. Whether the high-efficiency filter is placed inside the machine or at the end will also 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?。

Use boundary description instead of abbreviation when requesting quotation

You can write down the interface location, design air volume and whether the end filter is included in each item. Just writing 'a certain value of pressure' without indicating full pressure or static pressure may lead to two standards for equipment selection and on-site acceptance. When comparing samples with actual measurements, the air state and measurement conditions should also be unified.

The relationship between air volume and pressure is not linear. When the air volume changes, the total pressure, static pressure and dynamic pressure will change. Only the pressure value under one air volume is given, and the performance under other working conditions cannot be judged. When the air volume units are inconsistent, you can refer toHow to convert the air volume units of air conditioning box in m³/h, L/s and CFM? . How to determine the design air volume, please refer toIs the air supply volume of the air conditioning box determined based on the number of air changes or the cooling and heating load?。

How to avoid caliber confusion during on-site measurement

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 the two use the same caliber.

If the actual measured static pressure outside the machine is lower than the design value, it may be due to the deviation of the fan operating point, the increase in filter resistance, or the change in external air path resistance, which cannot be directly attributed to the fan itself. How to establish the fan pressure budget, please refer toHow is the total pressure of the air conditioning box fan determined by the internal resistance and external demand? . When the system resistance changes, 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?。

Aili industrial supporting equipment

When submitting pressure requirements to Aili Industrial, you can attach a resistance table or measurement point indication; the fan working point will be confirmed based on the internal configuration and external requirements. Aili Industrial can jointly check the fan, motor, filter and box structure, and indicate the pressure caliber, measuring point location and interface boundary in the selection data; the manufacturing end covers the independent research and development and production of motors and fans, control systems, sheet metal, air filters and complete machine assembly. The internal resistance of the machine and the external requirements of the machine can be aligned in the same set of packages.

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 pressure performance, applicable conditions 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.

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

Related questions and answers

Are external static pressure and total pressure the same thing?
no. Total pressure includes static pressure and dynamic pressure. External static pressure describes the pressure available for external systems outside the agreed interface. The calibers and measuring points of the two are different.

Can the equipment be selected if I only write a pressure value?
Not recommended. It is also necessary to indicate whether it is full pressure, static pressure or external static pressure, as well as the corresponding air volume, measuring points and interface boundaries, otherwise it is easy to adopt different standards for selection and acceptance.

Can Aili Industrial help check the pressure caliber?
The working point of the fan can be checked based on the resistance table, measuring point diagram and interface boundary. The specific plan needs to be confirmed according to the project technical agreement.

Related articles

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

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

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 you check and measure it first or increase the speed first?

Key points for selection and acceptance inspection