Sharp JX-9400 Informacje Techniczne Pobierz pdf (Strona 93)

measuring the air speed at several locations and integrating over the whole

opening or using a tracer gas.



þ 

pðz

dð

pðz

Þ¼0 ð4:26Þ

3 Windows open at the top level – the airﬂ ow through these windows, Q

,is

measured. We have similarly:



pðz

þ 

dð

pðz

Þ¼0 ð4:27Þ

The neutral plane is now at the top level.

Assuming that n is 0.6 or two-thirds, which are the most probable values, the

system of three equations above can be solved to estimate C

, a global C

and

. If the temperatures are not uniform inside or outside, Equation 4.21

should be used instead of Equation 4.22. The system is then more complex

but can still be solved. The most important condition to observe during the

measurement is the absence of wind.

The ma in advantage of the method is that it does not require the use of

sophisticated equipment. As a minimum, the required equipment is:

wind velocity meter, 0–5 m/s, for measuring the airﬂow rate in the openings;

diﬀerential manometers, 0–50 Pa;

air temperature thermometers;

length measuring device as long as the building is tall.

This equipment can be completed by more diﬀerential manometers and more

thermometers, used to verify the linearity of the pressure distribu tion through

the building.

Neutral height method

A simple vari ant of the stack eﬀect method oﬀers in many cases a good estimate

of the leakage area and determines if speciﬁcations are met or exceeded (Van der

Maas et al., 1994). It is also based on the determination of the neutral height

and the equipment necessary is only an airﬂow direction detector (small

smoke generator such as a cigarette, incense stick or small ﬂame) and a yard-

stick. With no wind, this method even allows the leakage characterization of

a single storey building.

The measurement should be performed with the mechanical ventilation

system switched oﬀ, preferably on a cold day without wind and when the

building is heated. In these conditions, the airﬂow through the building results

from buoyancy only. The method can also be used, mutatis mutandis, in cooled

buildings in a warm climate.

The principle is to determine the position of the neutral height in an out side

opening such as a door. The airﬂow direction detector is moved from bottom to

72 Ventilation and Airﬂow in Buildings

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