Sharp JX-9400 Informations techniques télécharger pdf (Page 84)

experiments is performed, enough equations can be written to compute the

airﬂows through the various measured parts for each pressure step.

For that purpose, the pressure steps should be the same in each experiment,

for example, 10, 30, 50 and 70 Pa. In order to get accurate pressure steps, the

fans speeds are automatically controlled. Since even this control cannot be

good enough to get accurate measurements (because of external and random

inﬂuences such as temperature or wind ﬂuctuations), the data should be auto-

matically selected and recorded only when the following conditions are

fulﬁlled:

The pressure in the room is equal, within a predeﬁned tolerance, to the

predeﬁned value of the pressure for each step.

The pressure diﬀerence between the room and the guarding zone is smaller

(in absolute value) than a predeﬁned small value.

Finally, for each pressure step and each conﬁguration, several values are meas-

ured and averaged to minimize the eﬀect of ra ndom nois e.

Determining the leakage coeﬃcients

Density corrections

It is the airﬂow through the fan, q

, which is measured and the airﬂow q

through the leak that is needed to calculate the leakage coeﬃcients. In pressur-

ization experiment s, the air blown by the fan comes from outside while the air

leakage comes from inside. In depressurization experiments, the opposite is the

case, but in both cases the temperature of the airﬂows may not be the same.

During the measurements, the mass of air is conserved and:



¼ q hence q ¼



ð4:4Þ

where 

and  are the densities of the air going respectively through the fan

and through the leaks. Since the density of the air is inversely proportional to

Figure 4.3 Principle of the guarded zone technique applied to several

walls of a room

Note: At the left, only the external wall is measured, while at the right, the right partition

wall is included in the measurement.

Airtightness 63

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Sharp JX-9400 Informations techniques Page 84