The core problem of compressor oper
The function and calculation method of air-conditioning ventilation static pressure box
1. What is a static pressure box?
Static pressure box, also known as plenum chamber, is a large space box connected to the air outlet. The flow velocity of the air flow in this space decreases to close to zero, the dynamic pressure is converted into static pressure, and the static pressure at each point is approximately the same, so that the air outlet achieves the effect of uniform air delivery. (Some are installed near the fan suction port, which also reduces the wind speed. The wind speed at the fan suction port is too high to prevent the impact of the airflow on the impeller).
Static pressure box is a traditional ventilation facility, which is often used in constant temperature, constant humidity, clean room and environmental climate room, which have precise requirements for indoor temperature, humidity, cleanliness and air distribution uniformity. General air conditioners have zero static pressure, no static pressure box is used, only high-power air conditioners such as 5HP have a long air supply distance, so it can be used to reduce the noise in the ventilation and air-conditioning system, and obtain uniform static pressure. Wind out, reducing dynamic pressure loss. It is a necessary accessory for the air supply system to reduce dynamic pressure, increase static pressure, stabilize airflow and reduce airflow vibration. Generally, it is made of galvanized steel sheet to make the air supply effect more ideal.
A stadium has a large grandstand area, more seats, and small and many air outlets. To meet the air supply requirements required by the grandstand, it is difficult to use conventional ducted ventilation systems. The ceiling space of the building under the audience is used to design the overall air-conditioning supply. Static pressure box air supply system. It makes full use of the characteristics of wide air supply area, large air supply volume, and low working noise of the static pressure box system, maximizes the use of building space and saves resources.
2. The function of static pressure box
1. Part of the dynamic pressure can be changed to static pressure to make the wind blow farther;
2. Lined with silencing material, which can reduce noise (noise reduction 10~20db (A));
3, the air volume is evenly distributed;
4. In actual ventilation systems and air-conditioning systems, there are often situations in which ventilation ducts change from square to round, round to square, reduce diameter, right-angle turns, and multi-pipe intersections, etc., all of which require specific pipe fittings to connect. The production of pipe fittings takes time and consumes materials, and installation is not convenient. At this time, the static pressure box is used as the pipe to connect them, which can greatly simplify the system, so that the static pressure box functions as a universal joint.
5. The static pressure box can be used to reduce noise and obtain a uniform static pressure to reduce the dynamic pressure loss. The static pressure box can be well applied to the ventilation system to improve the comprehensive performance of the ventilation system.
Three, the principle of static pressure box
The pressure generated by the irregular movement of air molecules and hitting the tube wall is called "static pressure". Static pressure makes the pressure perpendicular to the direction of fluid movement, and its role is to overcome the resistance in the process of fluid transportation. Then the purpose of establishing a static pressure box is to obtain static pressure. (Total pressure = dynamic pressure + static pressure: the total pressure of the fan is constant, the wind speed decreases, which means that the dynamic pressure becomes smaller, and the static pressure increases). When multi-air ducts supply air, in order to make the partial pressures of all ducts consistent, a static pressure box needs to be built to convert all dynamic pressure into static pressure, and then evenly distribute them to each duct. In the same way, when the multi-air pipe returns to the air, a static pressure box is also needed to make the air in front of the surface cooler fully mix. Some single air ducts are also equipped with static pressure boxes, the purpose is to use the static pressure box to muffle the sound, the principle is that the air entering the static pressure box quickly and obviously slow down, and the wind noise will be reduced.
The design principle of the static pressure box: The function of the static pressure box is to provide uniform pressure for each branch pipeline. Theoretically, the static pressure inside the static pressure box is equal, that is to say, the flow velocity inside the static pressure box is zero everywhere, which must be satisfied Under this condition, the volume of the static pressure box is infinite. This is impossible in engineering projects. Generally, the wind speed in the box can be controlled below 2m/s, or it can be greatly reduced relative to the wind speed of the inlet and outlet ducts.
1. When the air pipe needs a large diameter reduction, but the installation distance on site cannot meet the required length of the reduction, consider making a static pressure box;
2. When the air duct is connected to air conditioning equipment (PAU, AHU, FAN, etc.), it is usually connected by a static pressure box;
3. The inner sticking material in the static pressure box can be selected from rock wool, glass wool and other sound-absorbing materials according to the requirements. The surface is made of sheet metal with superior anti-corrosion performance.
Four, static pressure box calculation method
1. When designing the static pressure box, if the design is carried out according to the specified wind speed, the box body will be very large; the long side of the general static pressure box should be 400mm wide and the height of the wind pipe should be 400mm. Just an estimate.
2. The experience of the general old engineer of the static pressure box is 5~10db(a)/m, and the impedance compound type (it seems that air conditioning and ventilation systems generally use this) muffler 10~15db(a)/m.
3. Control the wind speed within 2.5. If the volume is too large, the wind speed can be appropriately increased. There is no other mandatory requirement for the length generally greater than 1m.
4. Height x depth = section area of static pressure box, section area of static pressure box x 2.5m/s = fan air volume, as to how to match the height and depth, you can grasp it yourself.
5. Using the air volume of the unit L÷3m/s, the area of one side of the static pressure box can be obtained, and then according to the height of the house, if it is 4 meters, the unit is 2 meters high, minus the soft joint about 0.5 meters. Leave 0.5 meters high, then your static pressure box is only 1 meter high, then you can determine the width, with two numbers, the third number is easy to determine, here z* mainly depends on your own The air-conditioning room is not enough space, if there is enough space, try to make it bigger! The calculation method of length is also the same. If you know the width, doesn't your width multiplied by the length also have an area? This area should also be equal to L/3, but the surface wind speed in the design institute is 2m/s. If there is enough space, make it larger.
6. The thickness of the static pressure box is preferably greater than 600mm, and the cross-sectional wind speed is less than 2m/s. In addition, pay attention to the airflow buffer between the connecting position and the connecting position.
7. In fact, the static pressure box we are talking about is just a metal box, not a static pressure box with silencing cotton. The cost may not be too important. If it is really a static pressure box with silencing cotton, then you have to consider the cost. For other mufflers, pay attention to the control of the flow rate. Most of them are controlled within 8m/s. As long as this value can be reached, the muffler effect will be good.
8. I think the noise reduction static pressure box is very necessary. Sometimes it is difficult to connect the pipe without using the static pressure box in the machine room. The noise reduction is only second. The cross-sectional wind speed should be less than 1.5m/s, and the aspect ratio should be less than as much as possible. 1:4;
9. The function of the static pressure box is to change the dynamic pressure into static pressure, and evenly distribute the air volume, which is mostly used in front of the slit tuyere;
10. The main function of the static pressure box is to stabilize and reduce noise. The specification seems to have that the wind speed in the static pressure box is not more than 2.5m/s. The volume of the static pressure box can be determined according to the air volume and wind speed. The static pressure box is generally customized. The width direction should not be smaller than 500mm. Usually the size of the static pressure box is slightly smaller than the indoor unit.
11. It adopts floor air supply. It uses two types of static pressure boxes, one is to use interlayer as static pressure box, and the other is to use ordinary static pressure box and connect several air pipes to the air outlet on the static pressure box.
