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ventilation rate. Maintaining air quality requires an increase in supply air,

leading to energy wastage.

Checking the airtightness of a building envelope or a duct network should

therefore be performed at each commissioning of a building or ventilation

system.

Measurement methods

The airtightness of the envelope of the measured object is in fact expressed by

its permeability to air, which is the relationship between the leakage airﬂow rate

and the pressure diﬀerential through the envelope of the object. This relation-

ship can be either expressed by a mathematical express ion (see Equations 4.1

and 4.3) or by an equivalent leakage area (see Equation 4.19).

One internationally standardized way to assess this permeability requires

the maintenance of a pressur e diﬀerential between the interior and the exterior

of the object with a fan, and the measurement of the airﬂow rate needed to

maintain this pressure diﬀerential (ISO, 1998). Other, simpler but less accurate

methods applicable to buildings are described below in ‘The stack eﬀect

method’. They use the stack eﬀect to create the pressure diﬀerential and open-

ings and the location of the neutral level (the level where the indoor–outdoor

pressure diﬀerential is zero) to estimate the leakage area.

The fan pressurization method

Before measurements are taken, all purpose-installed openings (doors,

windows, ventilators, etc.) should be closed, and the mechanical ventilation

system switched oﬀ (unless used for pressurization). The ventilation grilles

should either be sealed or all ventilation dampers should be closed. It may be

necessary to seal chimneys and ﬂues but these can be sealed later as part of the

test if desired. Clean up open ﬁres to avoid dispersion of ash in the rooms.

The pressure diﬀerential is cr eated by a fan installed in an opening of the

envelope of the object, or by the ventilation fans themselves. It is measured

with a sensitive manometer (range 0–100 Pa (Pascals) or 10 mm water

10%

20%

30%

40%

50%

60%

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Infiltration ratio

Figure 4.1 Measured part of outdoor air that is not supplied by the system

in mechanically ventilated buildings, shown with uncertainty band

Airtightness 59

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Sharp JX-9400 Informazioni Techniche Pagina 80