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case, the airtightne ss is not good enough and cold air enters the inhabited space

through cracks between wooden panels.

The stack eﬀect method

This simple and easy-to-install method to estimate the air leakage distribution

in tall buildings is based on the pressure distribu tion induced in buildings by

the stack eﬀect (Tamura and Wilson, 1966). Three parts can be estimated

separately: the ground ﬂoor, the top ﬂoor and the remaining ﬂoors.

The basic idea is to pressurize the building with the stack eﬀect, and to plan

three diﬀerent experiments where two airﬂows can be measured to get three

independent equations for the three diﬀerent leakages that will be estimated

(Hakajiwa and Togari, 1990).

For this measurement method, the building should be tall and the tempera-

ture diﬀerence between indoors and outdoors should be large enough, in suc h a

way that the pressure diﬀerence between inside and outside induced by the

stack eﬀect is larger than the pressure caused by the wind. Therefore, calm

weather should be preferred and the mechanical ventilation system switched

oﬀ. The pressure diﬀerence resulting from buoyancy is proportional to the

product of the indoor–outdoor temperature diﬀerence and maybe the stack

height. It reaches 30 Pa if the product of the height and the temperature diﬀer-

ence is 700 Km.

The leakage of the building is divided into three parts:

leakage through the ground level including the entranc e door (suﬃx g);

leakage through the top level including the roof (suﬃx t);

leakage through the remaining ﬂoors (suﬃx r).

If the building has all its internal doors open as well as the staircase and the lift

shaft, and if the temperature does not vary too much throughout the building,

Figure 4.7 Roof corner under depressurization

Source: Roulet, 2004.

70 Ventilation and Airﬂow in Buildings

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Sharp JX-9400 Technical Information Seite 91