10 Tips for designing HVAC ventilation systems-Part Two

6. Duct painting:

(1) Two coats of antirust paint (red lead antirust paint, iron red antirust paint, aluminum powder iron red phenolic antirust paint are acceptable) are applied on the inner surface of the thin steel air duct and the outer surface of the air duct that needs heat preservation. The non-insulated outer surface of the thin steel air duct is coated with an anti-rust primer and a second oil-based blending paint; the color of the paint should be coordinated with the painting and decoration of the room where it is located.

(2) The galvanized steel sheet may not be painted. However, the damaged part of the bite should be painted, and if corrosion has been found during construction, it should be painted.

(3) Remove the rust and oil from the rust before painting.

7. Fresh air inlet position:

(1) It should be installed in a relatively clean place outdoors, and the content of harmful substances in the outdoor air at the air inlet should not exceed 30% of the maximum allowable concentration of the indoor working place.

⑵ When arranging, keep the air outlet and air inlet as far away as possible. The air inlet should be lower than the exhaust air that discharges harmful substances.

(3) In order to avoid inhaling dust from the outdoor ground, the bottom of the air inlet should not be less than 2m away from the outdoor floor; when it is arranged in a green belt, it should not be less than 1m.

⑷In order to lower the temperature of the outdoor air inhaled in summer, the air inlet should be located in the shade of the building, and should be located on the north wall instead of on the roof and west wall.

8. Other requirements for fresh air outlets

⑴ Shutters should be installed at the air inlet to prevent rainwater from entering, fixed shutters should be used for the shutters, and waterproof shutters should be used in rainy areas.

(2) In order to prevent birds from entering, a metal mesh should be installed inside the shutters.

(3) For centralized systems that use a large amount of fresh air in the transition season, two fresh air outlets should be set up, one of which is the smallest fresh air outlet, and its area is calculated according to the minimum fresh air volume; the other is a fresh air outlet with variable air volume, and its area is calculated according to the maximum fresh air volume Subtract the calculation of the minimum fresh air volume (the wind speed can be made larger).

Examples of air duct design:

Example: fresh air unit, the air volume is 2000m3/h, the main air duct specification?

Take the wind speed as 5.5m/s, the cross-sectional area of the air duct: 2000m3/h÷3600÷5.5m/s=0.1010101m2=101010mm2,

Duct size: 500mm×200mm.

Calculate the wind speed according to the size of the air duct:

2000m3/h÷3600÷0.5m÷0.2m＝5.56m/s.

Within the specified range, the air duct is selected to be 500mm×200mm.

9. Air duct material: metal (galvanized steel plate, stainless steel...); non-metal (rigid polyvinyl chloride, glass fiber reinforced plastic, glass magnesium...); composite material (made of non-combustible surface layer composite insulation material board: phenolic, aluminum foil centrifugal cotton...) , Building air duct.

10. Smoke exhaust duct: The body, frame, fixing materials, and gaskets must be non-combustible materials. The thickness of the steel plate air duct is selected according to the high-pressure system, and the inspection and detection is according to the medium-pressure system.

Please use a CNC duct fabrication machine for duct fabrication. Duct fabricaiton machine is a CNC machine used to cut pre-insulated ductworks. If you use a duct fabrication machine for your pre-insulated ductwork, your duct making efficiency will be improved greatly. 

A pre-insulated duct making machine is an important tool to improve your duct making efficiency. There are many pre-insulated duct making machines in the market. Please make sure that you chooes the right pre insulated duct making machine for your ductworks. If you use a pre insulated duct making machine that is not user-friendly, you may end up spending more time for your pr-insulated duct making process.

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