Air change efficiency of room ventilation units

The purpose of this study is to investigate the air change efficiency of commonly used residential room ventilation units with tracer gas concentration decay method. Carbon dioxide was used as a tracer gas in both laboratory and field measurements. The performance of room ventilation units was compared to the conventional mixing ventilation. Therefore, the laboratory measurements were conducted with horizontal supply air jet from the overhead air diffuser on the fixed supply airflow rate with various supply air temperatures. The test results showed that nearly fully mixing ventilation was achieved. Furthermore, lower supply air temperature increased the air change efficiency. In next step, the air change efficiency of three room ventilation systems were measured in the test room. Tested systems included pair-wise units, monoblock unit and ventilation radiator, which was combined with mechanical extract ventilation. The measurements were carried out both during the heating period and outside the heating period. The results confirmed that all three solutions were capable of producing fully mixed ventilation. The air change efficiency was not affected by the variation of the air flow rate. Finally, tracer gas measurements were carried out in naturally ventilated apartments and the air change efficiency of these measurements were compared with the results of rooms based ventilation units.