Experimental study of air distribution and heating performances of deflection ventilation

Abstract

Deflection ventilation uses a purposely-designed deflector to divert supply air jet into the occupied zone directly. A few numerical studies have shown good indoor air quality with deflection ventilation. However, there was a lack of research on thermal comfort, which is also important to ensure human wellbeing. This study conducted experimental measurements when deflection ventilation was operated for winter heating. Eleven cases with different supply air velocities, supply air temperatures and deflection angles were carried out in an office-layout experimental chamber. As a comparison, another case with mixing ventilation was also measured. The predicted mean vote (PMV), draft rate (DR), air diffusion performance index (ADPI) and energy utilization coefficient (EUC) were adopted to evaluate the heating performances. The results showed that the deflection angle played a decisive role on air distribution. An inclined deflector (deflection angle: 35° downward) could elevate air temperature in the lower occupied zone as compared with a horizontal deflector (deflection angle: 0°), which provided efficient air distribution for winter heating. The average PMV values were in the range of −0.7 – 0.5, and the values of DR and ADPI in the occupied zone were typically less than 20% and higher than 80%, respectively. According to ISO 7730 and ASHRAE 113, deflection ventilation achieved satisfactory indoor environment with regard to thermal comfort. The EUC was typically greater than unity, indicating high energy efficiency of deflection ventilation, especially for the cases with deflection angle of 35°. In comparison with mixing ventilation, deflection ventilation can provide better thermal comfort as well as energy efficiency.