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Measured airﬂow rates diﬀer from the design values in many ventilation

systems. Figure 0.2 shows the relative diﬀerences between measured and

design outdoor airﬂow rate in 37 air handling units, i.e.:

Measured airflow rate  design airflow rate

Design airflow rate

These biases range from 79 per cent to þ67 per cent. Only 11 units are within

the 10 per cent range.

Recirculation rates

Some recirculation of air is often planned to di stribute heat or cold without

conditioning too much outdoor air. This, however, decreases the global

indoor air quality, since the contaminants generated within the building are

recirculated throughout the whole building. Therefore, recirculation may not

be desirable. In any case, recirculation should be controlled. Design and

100

150

200

250

300

0 100 200 300

Design airflow rate [m

/(h · person)]

Measured [m

/(h · p)]

Figure 0.1 Design and measured outdoor airﬂow rate per person in

12 buildings

Source: Roulet et al., 1999.

-100%

Percent bias

-50%

50%

100%

Figure 0.2 Relative diﬀerence between measured and design outdoor

airﬂow rate in 37 air handling units

Source: Roulet et al., 1999.

Introduction xv

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Sharp JX-9400 Informations techniques Page 16