Sharp JX-9400 Technické informace stáhnout pdf (Strana 90)

The overall airtightness of the structure and the size of the available fan

govern the maximum volume of enclosure that may be pressurized. Even if

large fans are available, in large leaky structures it may be possible to only

achieve a limited range of pressure diﬀerentials. Several resear chers have

used trailer mounted fans with maximum ﬂow capacities of about 25 m

/s to

examine buildings with volumes as large as 50,000 m

Internal fan

Because of the size and cost of trailer-mounted equipment and the inherent diﬃ-

culties of transportation and required manpower, other techniques have been

developed for the examination of large buildings. One method is to create the

required pressure diﬀerential using the building’s existing air handling system.

This technique relies on the building possessing a suitable mechanical ventilation

system, which can be adjusted to meet the needs of the measurement. Essentially,

the supply fans are operated while all return and extract fans are turned oﬀ and

return dampers closed (or exhaust ducts sealed) so that the air supplied to the

building can only leave through the leakage sites.

The analysis of measurement results proceeds along the same lines as that

for small buildings, but because of the large building volume it may not be

possible to achieve a pressure diﬀerence of 50 Pa.

Leakage visualization

Leakage can be visualized using infrared imaging, using a camera able to se e far

infrared radiation emitted by any surface. When reducing the intern al pressure,

outdoor air enters the building through leakage. Outdoor air, with a tempera-

ture that should diﬀer from indoor air, changes the temperature of surfaces

close to the leaks, thus making them visible, as in Figures 4.6 and 4.7 showing

the connection between two walls and the roof of a wooden building. In this

Figure 4.6 Roof corner from inside

Source: Roulet, 2004.

Airtightness 69

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Sharp JX-9400 Technické informace Strana 90