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in order to create a pressure diﬀerence large enough to minimize inﬂuences

from wind and temperature diﬀerences on the results. This pressure diﬀeren-

tial is built up and maintained by means of a fan, forcing airﬂow through the

envelope or comp onent to be evaluated. This ampliﬁed airﬂow can be put in

evidence by both qualitative (visualization) as well as quantitative (measure-

ment of the airﬂow for a given pressure diﬀerence) techniques in order to

assess the leakage locations, areas and characteristics.

External fan

The technique involves replacing an external door with a panel containing a

powerful, variable speed fan. Several commercial blower doors are now

available. These can be adjusted to ﬁt snugly into any domestic doorframe.

Airﬂow through the fan creates an artiﬁcial, uniform static pressure within

the building. Internal and external pressure taps are made and a manometer

is used to measure the induced pressure diﬀerential across the building

envelope. It has become common practice to test buildings up to a pressure

diﬀerence of 50 Pa.

Some means must also be provided to enable the volumetric ﬂow rate

through the fan to be evaluated. The aim of this type of measurement is to

relate the pressure diﬀerential across the envelope to the airﬂow rate required

to produce it (see ‘Determining the leakage coeﬃcients’, above).

The general conﬁguration for a pressurization/depressu rization test is

shown in Figure 4.5. The measurement procedure will depend upon the

purpose of the test and the exact equipment used.

The airﬂow required to produce a given pressure diﬀerence under pressur-

ization (airﬂow in) will not necessarily be identical to the ﬂow required to

produce the same pressure diﬀeren tial under depressurization (airﬂow out).

This diﬀerence is mainly due to the fact that certain building elements can

act as ﬂap valves. For example, some types of window will be forced into

their frames under pressurization while the reverse will be true for evacuation.

This implies that the actual leakage area of the building envelope will be a func-

tion of the type of test conducted. Hence, ideally, the fan and ﬂow measuring

mechanism must be reversible.

Figure 4.5 Schematic of building airtightness test

68 Ventilation and Airﬂow in Buildings

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Sharp JX-9400 Informazioni Techniche Pagina 89