Airflow characteristics and thermal comfort generated by a multi-cone ceiling diffuser with and without inserted lobes

Abstract

Mixing ventilation is commonly used to control thermal comfort in a room by means of air jets. In summer conditions, the occupants often complain of thermal discomfort and draft problems, because the cooling airflow penetrates the occupied zone under buoyancy force effect, with high speeds and low temperatures. To reduce these problems, the jet trajectory could be maintained away from the occupant, by means of a radial jet attached to the ceiling. One great limitation of most radial ceiling diffusers is their inability to correctly mix the jet to the ambient air, and the use of the Coanda effect may worsen this issue because it reduces jet induction. The design of the diffuser itself to enhance the jet mixing with the ambient air by means of inserted lobes was recently proposed in an European patent. In this paper, an experimental investigation is made on airflow pattern and thermal comfort generated in a full scale model room by a ceiling diffuser, and its performance is compared with the same diffuser equipped with inserted lobes. The jet flow from the diffuser and its interaction with a heated manikin simulating an occupant were analyzed with the whole-field PIV technique.Thermal dissatisfaction and draft effect were analyzed based on traditional pointwise measuring probes and the standards ISO 7730 and ASHRAE 55. It is revealed that thermal discomfort and draft sensation were substantially reduced using inserted lobes, without significant changes of pressure drop and sound pressure levels.