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duct leakage testing according to DW-144

duct leakage testing according to DW-144

duct leakage testing according to DW-144

(OP)
fellow engineers,

I've got a problem about duct leakage testing. we are testing ducts in our commercial building site according to DW-144. the test device is this ( http://www.tetisantesisat.com/measure-and-control-... ). A standart test fan coupled with an orifice plate.

the leakage formula on the device is calculated according to its orifice plate and it is : Q = 2,256 * dP^-2 Where Q is the leakage in m3/h and dP is the pressure difference on the orifice. so basically it is measuring the airflow on the closed duct to find the leakage.

everything is perfect until here. when we test a B-class duct on 1000 Pa, we have read the leakage as 240 Pa. the max allowable leakage is 0,8 l/s per m2 and 46 m2 is tested and calculated as 132,48 m3/h. if we calculate the leakage from the above mentioned formula it is 34,94 m3/h and thus passes the test. but if we make this from the reverse and use Qmax to find out what kind of pressure difference can make this test fail, we find 3448 Pa which is impossible.

So I thought that there must be another limit but can't find it. With DW-144 it is impossible to fail this test. Can anyone help me understand if I make any mistake.

Thanks in advance...

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