Experimental investigation of airflow pattern and turbulence characteristics of stratum ventilation in heating mode

Abstract

Stratum ventilation (SV) is feasible for heating applications. Owing to the downward supply vane angle and positive thermal buoyancy, the airflow characteristics of SV for winter heating can be distinct from those for summer cooling. This study aimed to investigate the airflow pattern and turbulence characteristics in a field environment chamber heated by SV experimentally. Twelve cases were studied with the room air temperature controlled between 19.9 and 24.3 °C. Air velocities and temperatures in the occupied zone were measured. Based on the measurements, draft risk (DR) and vertical air temperature difference between head and ankle levels (ΔT) were evaluated. The results show that the warm supply air jets were initially delivered to the zone below 1.1 m, but gradually ascended to the upper zone owing to the effect of positive thermal buoyancy. Consequently, the heights where the highest air velocity and temperature were measured varied with the distance from the supply inlets. As a result of the airflow pattern, the re-separation phenomenon of velocity spectra at different heights was observed at the far field from the inlets. These characteristics were different from those of SV for summer cooling. The airflow pattern illustrated that SV could warm the occupied zone efficiently, especially when the Archimedes number was less than 0.045. An appropriate reduction in the supply air temperature is recommended to achieve satisfactory local thermal comfort with ΔT and DR values conforming to the comfortable ranges as stipulated in ISO 7730–2005.