Experimental investigations and practical experiences in Europe have proved that hydronic cooled ceilings are able to remove high
cooling loads without impairing thermal comfort. As hydronic cooled ceilings cannot remove latent loads and pollutants, e.g., CO , 2
VOCs, odors, additional ventilation has to be applied. Often, displacement ventilation is used, which is able to provide lower pollutant
levels in the occupation zone than mixing flow systems, if the occupants are causing most of the pollution. Unfortunately, the advantage
of the displacement flow, in respect to the air quality, can vanish when cooled ceilings are used to remove the major part of the sensible
cooling load. For these applications, a combination of a cooled ceiling with a mixing ventilation system might be more appropriate. This
paper presents the results of an investigation examining the distribution of tracer gas in a test chamber which is equipped with a radiant
cooled ceiling. There is both a displacement flow system and a mixing flow system available, so that the concentrations of the tracer gas
within the occupation zone characterizing the air quality can be compared directly and evaluated under similar conditions. The vertical air
temperature rise is taken into consideration as well, as it influences the displacement flow and is an important issue for assessing thermal
comfort. The results show the interaction of the portion of the cooling load being removed by the supply air, the air quality in the
occupied zone and the vertical air temperature rise. The figures and tables presented show which of the two supply air systems
investigated have advantages over the other. q 1999 Published by Elsevier Science S.A. All rights reserved.