Sharp JX-9400 Informações Técnicas descarregar pdf (Página 162)

As an example, for an airﬂow rate of 100 l/h, that is 28  10

6

/s, the

minimum pipe inner diameter will be 2.6 mm to have an air speed of 5 m/s.

In this case, the pressure drop will be 420 Pa/m, which may be too large in

most buildings. A pipe with a 4 mm inner diameter will have an air speed of

2.2 m/s and a pressure drop of 80 Pa/m, which allows for 12 m long pipes

with a pump allowing 1000 Pa under pressure at 10 l/h.

Injection and sampling port locations

To ensure the best possible mixing of tracer with air in the measured zone, the

tracer gases should be injected at the locations where natural convection or

mechanical ventilation provides signiﬁcant air currents. Examples are ventila-

tion inlets and the bottom of heating devices.

Sampling locations should be kept away from injection points, but at

locations which are representative of the air in the zone or where mixing can

be reasonably assumed to be good. Ventilation exhaust grilles are generally

good locations.

If there is a convective loop in the measured room, it is convenient to place

injection and sampling points on this loop but at two opposite points. However,

the points should not be placed near a door or a window that can be opened

during the measurement.

In a two-storey building with an open staircase, the upstairs tracer injection

points should be placed close to the staircase, while the sampling points should

be near the outside walls.

To obtain a more representative sample, or to inject at several locations in

a zone, the sampling or injection pipe may be connected to a mixing box or

manifold, from which several pipes, of the same length and diameter, go to

various locations in the zone.

Injection and sampling sequence

Multi-zone tracer gas active measurement methods generally use only one

analyser and often single bottles of each gas. This requires the zones to be

scanned in sequence. There are several ways to plan these sequences, the two

extremes being sequential or simultaneous operation (see Figure 7.1).

In sequential operation, one zone at a time, the sample tube for a given zone

is pre-purged with a fresh sample prio r to analysis. After this, some tracer gas is

injected and the injection pipe is subsequent ly purged and the cycle repeated in

another zone.

The simultaneous operation applies mainly to the constant concentration

method. The air from zone i is pre-purged, while the air from the preceding

zone, i-1, is analysed. At the same time, the amount of tracer to be injected

to zone i-2 (already analysed) is calculated and delivered while the injection

pipe of zone i-3 (already injected) is purged. This strategy is much more

complex to control but is fast.

Common Methods and Techniques 141

1 2 ... 157 158 159 160 161 162 163 164 165 166 167 ... 210 211

Comentários a estes Manuais

Sem comentários

Sharp JX-9400 Informações Técnicas Página 162

Comentários a estes Manuais

Manuais e produtos relacionados com Digitalizar e Imprimir Sharp JX-9400