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What is supply air static pressure? What is the relationship between dynamic pressure and static pressure?
2025/10/10
I. Definition and Significance of Supply Air Static Pressure
Supply air static pressure, in simple terms, refers to the pressure exerted on the pipe wall perpendicular to the airflow direction when the gas flows in the air conditioning system during the supply air process. This pressure value reflects the system's ability to overcome pipeline resistance and drive air flow. In an air conditioning system, the magnitude of the supply air static pressure directly determines the supply air distance, the uniformity of the supply air, and the overall performance of the system. The significance of supply air static pressure lies in the fact that it is an important indicator for measuring the supply air capacity of an air conditioning system. A well-designed air conditioning system should be able to ensure the efficiency of air supply while achieving uniform air distribution indoors, thereby providing users with a comfortable and healthy indoor environment. The setting and optimization of the supply air static pressure is precisely the key to achieving this goal.
Ii. The Relationship and Principle between Dynamic Pressure and Static Pressure
Before delving into the static pressure of supply air, it is necessary for us to first understand the basic concepts of dynamic pressure and static pressure and their interrelationship.
1. Static pressure (Ps) : Static pressure is the pressure exerted by a fluid at rest or perpendicular to the direction of fluid flow. In air conditioning ducts, static pressure is manifested as the pressure exerted by the gas on the pipe walls in all directions. It is produced by the irregular movement of fluid molecules hitting the pipe wall. The magnitude of static pressure is related to factors such as the density of the fluid, temperature, and the size of the pipeline.
2. Dynamic pressure (Pd) : Dynamic pressure refers to the pressure generated by a fluid during its flow due to velocity. In an air conditioning system, dynamic pressure is manifested as the pressure converted from the kinetic energy of the gas when it flows. The magnitude of dynamic pressure is directly proportional to the square of the fluid's velocity; that is, the higher the velocity, the greater the dynamic pressure. There is a certain conversion relationship between dynamic pressure and static pressure. When the gas flow velocity increases, part of the static pressure will be converted into dynamic pressure to drive the gas flow. Conversely, when the gas flow velocity decreases, the dynamic pressure will decrease and be converted into static pressure. In an air conditioning system, the sum of dynamic pressure and static pressure is equal to the total pressure (Pt), which is the total energy that the fluid possesses during its flow.
Iii. Working Principle and Calculation Method of Supply Air Static Pressure
The working principle of supply air static pressure is based on the fundamental principles of fluid mechanics. In an air conditioning system, the fan drives air flow by rotating blades, creating a certain pressure. This pressure is manifested in two parts within the pipeline: static pressure and dynamic pressure. Static pressure is perpendicular to the direction of the airflow and is used to overcome pipeline resistance. Dynamic pressure, on the other hand, is parallel to the direction of the gas flow and is closely related to the velocity of the gas. The calculation of supply air static pressure usually involves multiple factors, including the performance of the fan, the size and layout of the pipeline, the air flow rate, and the fluid density, etc. To simplify the calculation, the following basic formula can be adopted for estimation:
The formula for calculating static pressure: Static pressure (Ps) = total pressure (Pt) - dynamic pressure (Pd). Here, the total pressure Pt is usually provided by the fan manufacturer and represents the total pressure at the fan outlet. Dynamic pressure Pd can be calculated based on the fluid's velocity V and density ρ : dynamic pressure (Pd) = 0.5 * ρ * V². It should be noted that this formula is simplified, and in actual calculations, more factors may need to be considered, such as pipe frictional resistance and local resistance. Therefore, in practical applications, it is usually necessary to combine experimental data and empirical formulas for more precise estimation.
Iv. Application and Optimization of Supply Air Static Pressure in the Air Conditioning Field
The application of supply air static pressure in the field of air conditioning is extensive and significant. The following are some specific application scenarios and optimization strategies:
1. Enhance air supply efficiency: By reasonably setting the static pressure of air supply, it can be ensured that air can overcome pipeline resistance and be smoothly delivered to every corner of the room. This helps to improve the efficiency of air supply and reduce energy consumption. In practical applications, the static pressure of the supply air can be optimized by adjusting the rotational speed of the fan, changing the size and layout of the pipeline, etc.
2. Optimize air distribution: The setting of supply air static pressure has a significant impact on air distribution. By adjusting the static pressure of the supply air, the air can be evenly distributed in the room, avoiding the occurrence of local over-cooling or over-heating. This helps to enhance the comfort and healthiness of the indoor environment.
3. Reduce noise: Installing accessories such as static pressure boxes at the air supply outlets can reduce the generation of noise by lowering the air flow rate. As a resistance muffler, the static pressure box can reflect and interfere with sound waves by taking advantage of the sudden change in the cross-section of the pipe and the principle of the expansion chamber, thereby achieving the effect of noise reduction.
4. System Commissioning and Optimization: During the installation, commissioning and optimization of air conditioning systems, the static pressure of supply air is an important reference index. By monitoring and adjusting the static pressure of the supply air, problems can be detected and resolved in a timely manner, ensuring the normal operation and optimal performance of the system. For instance, when problems such as uneven air supply or excessive noise are detected, solutions can be sought by adjusting the static pressure of the air supply.
5. Energy Conservation and Environmental Protection: A reasonable setting of supply air static pressure helps to reduce the energy consumption and emissions of the system. By optimizing the air supply path and reducing unnecessary resistance losses, the energy efficiency ratio and environmental protection performance of the system can be improved. This is of great significance for promoting green buildings and sustainable development.
V. Conclusion
Supply air static pressure, as one of the core elements of air conditioning systems, plays a significant role in evaluating system performance, optimizing supply air effects, and enhancing user comfort. By thoroughly understanding the definition of supply air static pressure, the relationship between dynamic pressure and static pressure, its working principle, calculation method, as well as its application and optimization strategies in the air conditioning field, we can better apply this parameter to guide the design and operation practice of air conditioning systems.
