Air duct design & noise reduction
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delivery/return port and air delivery/return hose, for isolation of vibration.
Problem 2: Unreasonable design of air speed
Careful design of air speed at air delivery/return main duct, branch duct and ports according
to conditioned area noise requirement and unit air delivery static pressure is not carried out,
causing higher air speed and higher noise caused thereby.
Solution:
Design air duct and air port air speed according to national standard, “Product installation and
operation manual” and “Chunlan hole (commercial) centralized air conditioning system
design code”. Data in Tables 1 to 6 in this manual can be used for design reference (slight
deviations will not affect design). Design and type selection of air ducts and air ports shall
follow the following 3 steps:
(1) Roughly calculate air duct cross sectional area and areas of air delivery/return ports
according to unit rated air flow and suitable air speed;
(2) Reference “National common ventilating air duct calculation table” for preliminary
determination of air duct size and dimensions; reference manufacturer product samples for
preliminary determination of air port size;
(3) Calculate air resistance in air delivery/return systems. Further verify correct type selection
of air duct and ports by referencing unit air exhaust static pressure. When necessary, repeat
above 3 steps.
Problem 3: Local high resistance in air duct
Improper design of local resistance members such as air duct elbow, reducing pieces and T
branches etc. causing large eddy current and hence high air flow noise.
Solution:
(1) Avoid sharp turning of pipeline at indoor unit entrance/exit;
(2) Arrange diffuser or reducing tube of suitable length at reducing segment of air duct to
avoid sudden expansion or reducing of air duct;
(3) At elbows and T branches etc., take even-flow measures such as transition arc or flow
guide piece;
(4) Reduce or eliminate regulating valves.
Problem 4: Proper silencing measures not taken for pipeline system
In case of high noise requirement, silencing devices such as static pressure box, return air box,
silencing straight tube, silencing branch tube, silencing elbow or silencing air port are not
provided or incorrect or unreasonable.
Solution:
(1) When permitted by installation space, static pressure box and return air box (designed
section air speed not exceeding 2-2.5m/s) to requirements as much as possible. Inside these
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