Sharp JX-9400 Informações Técnicas descarregar pdf (Página 28)

do not change during the measurement campaign. This section describes ways

of interpreting the records of tracer gas injection rates and concentration in the

diﬀerent zones to get the airﬂow rates between zones, as well as airﬂow to and

from outdoors. For more information on tracer gases and analysers, see

Chapter 7, ‘Tracer gas dilution techniques’.

Let us assume that there are N zones in the measured building, denoted by the

suﬃxes i and j, into which, in principle, N diﬀerent tracers, denoted by the index

k, are injected. In principle, each zone receives only one tracer, but the equations

presented below allow the use of several gases in the same zone. No tracer is

injected in the outside air (zone 0), which is assumed to be of inﬁnite volume.

However, the tracer concentration in that zone may diﬀer from zero.

The multi -zone tracer gas theory is based on the conservation of the mass of

tracer gas and of air and on the following three assumptions:

1 In each zone, tracer concentrations are always homogeneous.

2 The atmospheric pressure is constant.

3 The injection of tracer gas does not chang e the density of air.

The ﬁrst assumption is the weakest. In practice , homogeneous concentration

may only be achieved by the use of mixing fans, but these fans may aﬀect

inﬁltration conditions.

The other two hypotheses are easily satis ﬁed because the short-time relative

variations of atmospheric pressure are of the order of 0.01 per cent (daily

variations of the order of a per cent) and tracer gases are generally injected at

relatively low concentrations (10

4

or less).

Conservation of the masses of air and tracer gas k in zone i

In each zone, the ra te of change of the air mass m

equals the sum of the

incoming ﬂows minus the sum of the outgoing ﬂows:

j ¼0

ð1  

Þ

j ¼0

ð1  

Þð1:23Þ

Change

in mass

Incoming

flow rates

Outgoing

flow rates

where 

is equal to one only when i ¼ j, and zero otherwise. The sum is then

over all terms for which i 6¼ j. Note that, in most cases, the left-hand side of

these equations is close to zero and can be neglected.

The conservation equation of the mass of tracer, k, in the zone, i, states that

the change of tracer mass within the zone is the sum of the mass of injected

tracer and the mass of tracer contained in the air entering the zone, minus

the mass of tracer contained in the outgoing air:

¼ I

j ¼0

ð1  

ÞC

j ¼0

ð1  

Þð1:24Þ

Variation Injection Inﬂow Outﬂow

Airﬂow Rates in Buildings 7

1 2 ... 23 24 25 26 27 28 29 30 31 32 33 ... 210 211

Comentários a estes Manuais

Sem comentários

Sharp JX-9400 Informações Técnicas Página 28

Comentários a estes Manuais

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