In the construction process of clean air-conditioning metal air duct, only according to its use requirements, take strict quality control measures to ensure its quality requirements.
Generally speaking, the metal air duct of clean air conditioner has four different requirements compared with the metal air duct of general air conditioner:
1. Keep the air duct clean
2.2. High sealing requirements;
3.3. High flatness requirements
4.4. The static pressure in the air duct is high.
This paper mainly discusses the guarantee measures and detection methods for the sealing of metal air duct of clean air conditioner.
1. Guarantee measures for sealing of metal air duct of clean air conditioner
(1) the form of air duct bite is single bite and joint angle bite.
(2) the metal air duct is connected by angle steel flange.
(3) when the plate size can meet the blanking requirements and the loss rate is not too large, it can be considered to make the elbow, tee and other accessories into a whole with the straight-line section to reduce the flange interface.
(4) the vertical seam shall be minimized in the production of air duct, and there shall be no horizontal seam. When the side length of rectangular air duct is less than or equal to 900mm, its bottom panel shall not have joint, and when it is greater than 900mm, it shall not have transverse joint.
(5) apply sealant (such as neutral glass glue) to the seam of air duct, such as seaming seam, rivet seam, four corners of flange flanging, etc. Before applying sealant, the dust and oil stain on the surface shall be removed.
(6) the flange gasket shall be 5mm rubber plate or 8501 flame-retardant sealing tape.
(7) when the air duct is connected with the flange, the flanging of the air duct shall be flat and close to the flange, and the width shall not be less than 7mm
(8) the distance between flange screw hole and rivet hole shall not be greater than 100mm. Screw hole shall be set at four corners of rectangular flange. Guide vanes shall be set in elbow, tee and other pipe fittings and fixed with flat head rivets. It is strictly prohibited to use pop rivets. Apply sealant to rivets.
(9) the soft joint is connected by angle steel flange.
2. The light leakage method is used to detect the tightness of the metal air duct of the clean air conditioner after the air duct is hoisted and before the heat preservation. The light leakage is detected in sections. According to the smooth degree of cable pulling in the air duct, the detection length of the air duct can be segmented as long as possible to reduce the number of detection and improve the working efficiency. The key parts to be inspected are bends, tees and other pipe fitting plate turning points, flange corners flanging and rivets. According to Appendix A of code for acceptance of construction quality of ventilation and air conditioning engineering (GB50243-2002), every 10m joint of medium voltage system, the light leakage point is no more than 1, and the average 100m joint is no more than 8, which is qualified. However, the regulation can not meet the requirements of air leakage test. Therefore, before using the air leakage test, it should be ensured that there is no light leakage point.
3 air leakage test
3.1 instrument for air leakage test
The following describes the air leakage test device used by the author (Figure 2). For the assembly of the device, please refer to the appendix of code for construction and acceptance of clean room (jgj71-90), positive pressure air duct type air leakage test device.
(1) test centrifugal fan 9-19 № 4a (1704m3 / h, 3253pa, 3KW)
(2) pitot tube and inclined micro manometer (yyt-200b, 0 ~ 200mmh2o)
(3) thermal ball anemometer (qdf-3, 0.05 ~ 30m / s)
3.2 method of air leakage test
(1) first use galvanized steel plate to block and test each outlet of air duct. Then connect the air inlet pipe of the air pipe leakage test device with the test air pipe, use the test centrifugal fan to blow air into the air pipe, and adjust the air volume regulating valve at the fan inlet. Raise the static pressure P in the air inlet pipe and keep it at 700pa
(2) the static pressure in the air inlet pipe shall be measured with pitot tube and inclined micro manometer.
(3) the wind speed of the air inlet pipe shall be measured by the hot ball type electric anemometer. According to the measured wind speed and the cross-sectional area of the air inlet pipe, calculate the air inlet volume Q (m3 / h). At this time, the air intake q is the air leakage.
4. Calculation process of air leakage 4.1 judgment of air flow pattern
∵ the air volume of the test fan is 1704m3 / h, and the diameter of the air inlet pipe is φ 300
★ wind speed v = 6.7m/s
And ∵ 1 atmospheric pressure, the kinematic viscosity coefficient of 30oC air = 16.6 * 10-6 (m2 / s)
∴Re===121084
(Re > 2000)
The flow pattern of the air is turbulent, and the calculation formula of the flow cannot be considered as laminar flow. The general section of the velocity distribution in the air duct is shown in Figure 3.
4.2 determination of air leakage
The size of air leakage shall be considered as the sum of the volumes of one cone and one cone platform as shown in Figure 4.
Q measurement - air leakage (m3 / h)
D - diameter of air inlet pipe (m)
V1 - wind speed at the center a of the air inlet pipe section (M / s)
V2 - wind speed at Section B of air inlet pipe (M / s), and the distance between point B and point a is D / 4
Q test = 3600 {π() 2 (V1-V2) + [π() 22v2 - π() 2v2]}
=3600π（v1+6v2） （m3/h）
=75πd2（v1+6v2） （m3/h）
4.3 air leakage calculation formula of the air leakage test device
Q measurement = 21.2 (V1 + 6v2) (m3 / h).
5. The qualified standard of air leakage test shall be in accordance with the provisions of the code for construction and acceptance of clean rooms (jgj71-90): the air leakage rate of the system with cleanliness of class 1000 (including class 1000) to less than Class 100 is η ≤ 2%; the air leakage rate of the system with cleanliness higher than Class 100 (including class 100) is η ≤ 1%
Calculation formula of air leakage rate: η = q ÷ Q amount × 100%
Q amount - design air volume (m3 / h)
6. The conversion formula of air leakage when the static pressure P cannot be maintained at 700pa. When the static pressure cannot be maintained at 700pa, the conversion shall be carried out. The static pressure during the test shall be kept at a certain p value (PA). According to the measured Q value, the air leakage Q when the static pressure is 700pa shall be converted according to the following formula
Q = q measurement (700 / P) 0.65 (m3 / h)
7 another qualified standard for air leakage test is according to code for acceptance of construction quality of ventilation and air conditioning engineering (GB50243-2002), air duct system is divided into three pressure levels: high, medium and low. Under different working pressure levels, the air leakage Q '(m3 / h m2) of unit area air duct in unit time should meet three different formulas respectively. Generally speaking, the clean air conditioning system is medium pressure system. Therefore, the formula Q ′ ≤ 0.0352p0.65 (m3 / h m2) of medium pressure system shall be met. Here P refers to the working pressure of the system.
Q‘=（m3/h m2）
S - surface area of test air duct (M2)
The test method and calculation formula of air leakage are the same as the above.
8. The test conclusion adopts scientific test method to test the airtightness of air duct, so as to make the construction quality of air duct meet the requirements of specifications.
(1) if the air leakage test fails to meet the qualified standard, blow air into the air duct, listen to the sound, cover each suspected air leakage point with the palm of your hand; put the bulb in the air duct again and observe the air leakage point with the naked eye. Then, apply sealant to the air leakage and tighten the flange bolts. If it is impossible to repair, it shall be removed and reassembled. Finally, test the air leakage again until it meets the requirements.
(2) the instrument of the air leakage test device is common and convenient for assembly and measurement; the calculation formula of air leakage is simple and easy to calculate.
(3) the air leakage measured by the air leakage test device is slightly smaller than the actual air leakage. However, through practical inspection, as long as the measured air leakage meets the qualification standard of any one of the two specifications mentioned in this paper, the airtightness of air duct can fully meet the use requirements and regulation requirements.
(4) only when the construction is carried out in strict accordance with the national construction specifications, and the above mentioned air duct sealing assurance measures are taken, can the qualified standard of air leakage be achieved.
(5) the larger the surface area of the detected air duct, the slower the pressure rise and the greater the air leakage.
(6) for the qualified system, the air volume of the general fan has been increased by about 10% during the design, so the actual measured total air volume is often larger than the design air volume.
Shandong ed purification Engineering Co., Ltd. is committed to medical purification engineering, laboratory system engineering, clean workshop system and other fields. After years of development, it has accumulated rich industry experience and won the honors of "China 3.15 consumer trustworthy products", "2017 excellent engineering company in HVAC purification industry", "2017 listing Award of enterprise share reform market", etc. it is clean Strong enterprises in the engineering industry. For more knowledge of medical purification industry, please pay attention to WeChat public address: Aide-188 (Ed purify oxygen supply).
