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Airﬂow Rates in Buildings

This chapter intends to help the reade r to measure airﬂow rates and air change

rates in buildings and room s, independently of a mechanical ventilation system.

It presents the techniques used to measure the airﬂow rate entering the

measured zone (single-zone measurements) and to measure inter-zone airﬂows

(multi-zone measurements).

A building zone or a zone is a space that can be considered as homogeneous

from the point of view of air quality or , more technically, a space in which each

tracer gas is homogeneously distributed. In practice, it is a room or a set of

adjacent rooms that have much larger airﬂow rates between them than to or

from other zones or the outdoor space.

The measurement techniques presented here are all based on the use of

tracer gases that are injected into the air and analysed in air samples after

mixing. More detailed information on the tracer gases themselves, on appro-

priate injection and sampling methods and on tracer gas analysers is given in

Chapter 7, ‘Tracer gas dilution techniques’.

Single-zone measurements

The tracer gas is injected in a space, mixed into the air and its concentration is

measured. Various strategies can be used for assessing the airﬂow rate entering

the space: recording and interpreting the concentration decay after having

stopped the injection, monitoring the tracer gas concentration when injecting

the gas at constant rate, or measuring the tracer gas ﬂow rate required for

keeping its concentration constant. Airﬂow rates are obtained by interpreting

the evolution with time of either the tracer gas concentration or the injection

rate. The interpretation methods are based on the mass conservation of

tracer gas and of the air.

Mass conservation of tracer gas and air

The tracer gas injected in a building space is uniformly mixed into the air. The

conservation of the mass of tracer gas within a single zone in contact with the

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Sharp JX-9400 Technical Information Seite 22