Static pressure box is also called the plenum, connect the air supply outlet box of large space. Airflow velocity decrease close to zero in this space, dynamic pressure into static pressure, static pressure at various points and approximation, the same air supply outlet is made to reach the effect of uniform air supply. (some near the suction fan, also play a role reducing wind speed, fan inlet wind speed is too high, to prevent air impact on impeller.) Static pressure box is a kind of traditional ventilation facilities, is often used in constant temperature, constant humidity, clean room and this kind of environment climate chamber to indoor temperature, humidity, cleanliness and air distribution uniformity have precise requirements of air conditioning wind system, the general air conditioning is zero static pressure, with less than static pressure box, only the power of the air conditioning, such as 5 HP air supply distance, so it can be used to reduce noise in ventilation, air conditioning system, and can obtain uniform static pressure of the wind, reduce the pressure loss. Is the air supply system to reduce dynamic pressure, static pressure, stable air flow and reduce airflow vibration of a necessary accessories, general use galvanized steel to make, can make the air distribution effect is more ideal. Engineering example: a stadium bleachers, larger area seat is more, supply air with and more, needed to satisfy the stands of supply air requirement, the conventional pipe ventilation system is difficult to achieve, use of audience under the building roof space, design of the air conditioning air supply plenum air supply system as a whole. Make full use of the plenum system supply air flux, the characteristics of big air volume, small noise, maximize the use of architectural space, save the resources.
Plenum role:
1, can put the part of the dynamic pressure into static wind farther;
2 and lined with anechoic material, and can reduce noise (decrease the 10-20 db (A));
3, air flow uniform distribution;
4, in the actual ventilation system and air conditioning wind system, often meet ventilation pipe change round, round
Party, variable diameter, right-angle bend, multi-tube intersection situation, such as all need to have specific fitting to connect, these specific
Pipe fittings production, time-consuming and consumable material, installation convenience. Even by using static pressure tank as fitting at this time
After them, can greatly simplify the system, so that the plenum have the effect of a kind of universal joint.
5, static pressure box can be used to reduce the noise, and can obtain uniform static pressure of the wind, reduce the pressure loss, the
Plenum well applied to the ventilation system, can improve the comprehensive performance of the ventilation system.
Principle of static pressure box
Due to the motion of the irregular air molecules hit the wall pressure generated by the called "static". Static pressure is vertical
Straight from the pressure of the fluid movement direction, is used to overcome the resistance in the process of fluid conveying. So establish plenum
Is to get the purpose of the static pressure. (= full pressure dynamic pressure + static pressure: fan total pressure is constant, the wind speed is reduced,
Means that the dynamic pressure decreases, the static pressure increased. ) When more duct, in order to make the air duct of wind pressure is consistent,
Need to establish a static pressure box, make all into static pressure and dynamic pressure evenly into the duct again. Similarly, in
More duct air return, also need static pressure box, can make the table in front of the cooler air mix. Some of the single duct
Wind pipe is to static pressure box, the purpose is to use the plenum silencing, principle is the air into the static pressure box speed significantly
Slow down, the wind will decrease.
The design principle of static pressure box:
Plenum of the role is to provide uniform pressure for each branch pipe, theoretically plenum internal static pressure
Equal everywhere, that is to say, plenum internal flow velocity is zero everywhere, to satisfy this condition is a plenum volume
Infinity. This is not possible in the project, generally in the wind speed can be controlled below 2 m/s, or phase
For in and out of the air duct wind speed can be greatly reduced.
Plenum characteristics and technical performance
1, duct need larger diameter changes, but the site installation distance and can meet the length, diameter changes required to consider making plenum;
2, air duct and air conditioning equipment (PAU, AHU, FAN, etc.) interface, usually by connection of the static pressure box;
Post material within the 3, static pressure box, can choose according to the rock wool, glass wool and other sound-absorbing material, the surface of sheet metal, superior anti-corrosion performance.
The plenum calculation method
1, in the design of static pressure box, if according to the provisions of design wind speed ChengJinHang, casing will be a lot; General plenum long edge to air outlet side 400 mm wide, height to the duct height 400 mm wide, just estimate.
2, static pressure box, Generally the old engineer experience is 5 ~ 10 db (a)/m, impedance compound (seems to air conditioning and ventilation systems are generally use this) muffler is 10 ~ 15 db (a)/m (3, control of wind speed within 2.5 If bulk can be appropriately increase the wind speed About length is generally greater than 1 m no other force
Depth of 4, height x = plenum section area, static pressure box section area by 2.5 m/s = fan air volume, as for the height and depth how to match, his grasp.
5, use your air volume of the unit L present 3 m/s, can get you a static pressure box surface area, and then you according to the height of the house, if is 4 meters, can be your unit is 2 meters high, in the minus the soft joint is about 0.5 meters, 0.5 meters high above leave, that you only 1 meter high static pressure box, you can determine the width, with two Numbers, the third number is easy to determine, here is the most important is to see their own air conditioning room enough position, if have enough position, as far as possible big point!! The calculation method of length is the same, you know the width, then
You multiplied by the width of the length do not even have a area? This area should also be equal to L / 3, but in the design of the college, the face of the wind speed is taking 2 m/s, if enough space, be bigger.
Best is more than 600 mm, the thickness of 6, static pressure box section wind speed is less than 2 m/s, and pay attention to pick out the location and access between airflow buffer.
7, but now says the plenum only tin trunk, not with a quieter cotton plenum, cost may not be too critical, if is really put the mute cotton static pressure box, then think about the cost, in addition the muffler to pay attention to the control of flow rate, most are controlled within the 8 m/s, as long as can reach this number, sound attenuation effect is good.
8, I think it is necessary to silencing plenum, inside the room without the use of plenum sometimes it is hard to pick out lines, silencing is second, best section wind speed is less than 1.5 m/s, the ratio is less than 1:4 as far as possible;
9, the action of static pressure box is laid static pressure and dynamic pressure uniform distribution of air volume, how to sew before tuyere;
10, static pressure box is the main function of voltage stability, noise reduction. There seems to be a specification, static pressure in the wind speed is not more than 2.5 m/s, according to the air volume, wind speed can determine the volume of static pressure box, static boxes are usually custom-made. Small 500 mm width is unfavorable. Usually the size of the plenum than indoor machine can be slightly smaller.
11, with floor board air supply and its static pressure box adopts two kinds, one kind is to use interlining as static pressure box, another use ordinary plenum and then pick up a few duct to the air supply outlet on the plenum.
