Airflow and air temperature distribution in the occupied region of an underfloor ventilation system

Measurements were carried out in an office-type experimental room ventilated by a floor return-type underfloor ventilation system to investigate the distributions of airflow velocity and air temperature. A fan-powered floor air unit (FAU) with rectangular supply and return air outlets covered by straight-profile linear bar-type air diffusers was installed to deliver the conditioned air in the experimental room. Turbulence intensity and draught rate distributions inside the room were also calculated by using the measured data. From the experimental results, it is found that undesirable high air velocities and high draught rates were created within a small region near the supply outlet of the FAU. Temperature differences between different height levels were maintained within an acceptable comfort level under the tested supply air conditions and heat loads. The results indicated that the temperature stratification could be maintained at an acceptable comfort level by designing the supply air conditions properly. A clearance zone is suggested as a design consideration for locating the FAUs and occupants to avoid undesirable draught discomfort to the occupants.