height at axis 1. The profiles indicate that almost the entire
fresh air is being drawn up by the thermal plume of the
heat sources, which were mostly situated close to the
supply air inlet. The rest of the room except the floor Ž
area did not get fresh air, but already mixed air. There- .
fore, all other relative contamination efficiencies are very
close to 1.0, indicating that there is no significant difference
between the displacement flow and mixing flow in
terms of air quality.
In fact, a distinct recirculation of rising room air to the
lower part of the room was observed with displacement
flow, especially at the walls. This marked recirculation is
typical for the airflow pattern in a space with a cooled
ceiling removing the major portion of the cooling load and
occurs due to three reasons. First, the convective heat
exchange at the cooled ceiling cools the rising air, which
makes it to flow back down. Second, the radiant heat
exchange cools the walls, causing buoyant airflows down- Ž
wards . Third, the buoyant airflow of the heat sources . 9 amounts to much more than the supply airflow Žs
exhaust airflow so that, a remarkable flow of room air has .
to recirculate in the test chamber. These mechanisms are
correlated with each other, so it is hard to tell which
influences or causes the other.
The slot diffusers mixing flow forced the introduced Ž .
supply air mainly to flow along the ceiling and then down
along the walls, so that it was not possible to distinguish