Sharp JX-9400 Technical Information PDF herunterladen (Seite 95)

that T

> T

, by:

Q ¼ Q





1=2



1 



3=2







3=2

ﬃ Q

ð1  aÞ

3=2

 a

3=2

ð4:29Þ

with a ¼

where z

is the height of the neutral level.

The opening area between this neutral level and the mid-height of the

opening is close to the equivalent leakage area. If the leakage is small, the

sensitivity can be increased by reducing the width of the opening, for

example by partly closing the door.

A neutral height below the mid-height of the test opening means that most

of the leakage area is below the opening. If the other leakages or openings are

larger than the test opening, the neutral height will not be found within the

test opening, even when this is wide open. In this case, a walk through the

building is necessa ry to identify and, if possible, to close or seal these large

openings.

The equivalent area measured this way is the diﬀerence between the equiva-

lent areas of the openings or leakage areas located above and below the opening.

Therefore, it is useful to make this measurement at two test openings located at

the bottom and the top of the building.

Measurement of airtightness of a duct or network

To ensure that fresh air reaches the ventilated space, thus ensuring acceptable

air quality, and to avoid energy waste when the air is either heated or cooled, the

duct network should be airtight. Signiﬁcant energy may be wasted, for

example, where leaky ductwork passes through an unheated space such as an

attic, basement or crawl space. As an example, it was found that ductwork is

the most signiﬁcant source of leakage in western US houses, together with ﬁre-

places (Dickerhoﬀ et al., 1982). Modera (1989) conﬁrms these ﬁndings, but

some houses were nevertheless found to be acceptable.

Several techniques allow for the checking of the airtightness of air duct-

work. In Finland, the airtightness of the ventilation system has to be checked

when commissioning the system (NBCF, 1987), but in most countries,

measurements are seldom carried out. ASTM (2003) provides guida nce to

perform such tests. Some measurement methods are described below.

Pressurization method

The principle of this method is a combination of those principles described in

Chapter 2, ‘Measurement for airﬂow rate in a duct’ and Chapter 4, ‘The fan

pressurization method’, above. All intakes, supply terminals, exhaust and

extract terminals connected to the system should be careful ly sealed, for

74 Ventilation and Airﬂow in Buildings

1 2 ... 90 91 92 93 94 95 96 97 98 99 100 ... 210 211

Kommentare zu diesen Handbüchern

Keine Kommentare

Sharp JX-9400 Technical Information Seite 95

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Drucken & Scannen Sharp JX-9400