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a displacement ventilation system, as shown in Figure 3.6. The conference

room is 8 m by 10 m wide and 3 m high. It is completely embedded in an old,

massive building. Its walls, ﬂoor or ceiling have no contact with the outdoor

environment. It has no windows, but leaky entrance doors leading to a hall.

The mechanical displacement ventilation system includes two low-velocity

air inlets, 1 m high, put at the ﬂoor level against one wall of the room. The

air, slightly colder than the room temperature, is introduced at low speed

close to the ground through three inlets . This cold air spreads on the ground

like a lake, and should go up faster where there are heat sources like occu-

pants. This asymmetric disposition does not allow a uniform distribution of

fresh air in the room, but was ﬁrst adopted for practical reasons, the building

layout not allowing an optimum location of air inlets and outlets. Five

exhaust grilles are located in the ceiling. Since the building owner was

interested in assessing the actual performance of the new system, age of air

measurements were performed in order to check if the airﬂow pattern in the

room was as expected.

First, age of air measurements were performed in the room as it was. It

was found that the air was poorly distributed in the room because of the

asymmetrical dispos ition of inlet grilles. In addition the doors were found to

be leaky, and much air from the ventilation system was leaving the room

quickly after entering it, thus reducing the purging eﬀect. The indoor air

quality was, however, good, since the ventilation rate was very high (eight

minutes nominal time constant, or 15 outdoor air change per hour, or 60 m

per occupant at full occupancy!).

On the basis of these results, improvements were brought to the system.

The leakages in the room envelope were sealed, a door was added, a new

inlet was added on the wall opposite to the existing inlets, and an exhaust

grille was added in the ceiling as shown in Figure 3.7.

A second measurement campaign was performed, showing a signiﬁcant

improvement of the ventilation eﬃciency (see Figure 3.8). The air change

Hall

Air inlets

Exhaust grilles

Office

Conference

room

Figure 3.6 Arrangement of the conference room and of its surroundings

Source: Roulet et al., 1998.

48 Ventilation and Airﬂow in Buildings

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Sharp JX-9400 Technical Information Seite 69