Experimental Study of Flow Characteristics of a Diffuser for Under Floor Air-Conditioning System

Under floor air conditioning (UFAC) is an air distribution system delivering conditioned air from floor level. This system has many advantages over a traditional ceiling supply system because diffusers are placed closer to the occupied zone. In a UFAC system, the role of diffusers becomes very important since it affects the distribution of indoor air more directly. It is well known that proper distribution of conditioned air plays an important role in the comfort of occupants and the air quality of indoor spaces. Since the same diffuser is used for heating and cooling in a UFAC system, it is important to design diffusers that are suitable for both purposes. Depending on heating and cooling conditions, flow direction and swirl strength need to be controlled to enhance indoor thermal comfort. In this study, a new diffuser for the UFAC system is developed and flow characteristics for isothermal conditions are studied. The new diffuser consists of two sections - an internal section for generating swirl flow and an edge section for vertical flow. By controlling the volumetric flow rate of each flow component, flow direction and swirl strength can be controlled. Flow characteristics are measured using an omnidirectional anemometer and a three-dimensional ultrasonic anemometer. The experiment is conducted to observe velocity distribution, velocity decay, angle of discharge, and induction for two different flow rates (120 cm/h and 180 cm/h). The flow visualization experiment using a paraffin oil was carried out to study the discharge angle. Results show that the newly developed diffuser has characteristics that are required for a UFAC system.