Numerical Simulation And Optimization On Underfloor Air Supply System In Gymnasium Buildings

Displacement ventilation possesses merits that include providing enhanced air quality, operating with higher energy efficiency, as well as offering greater convenience and flexibility; hence, it meets the ventilation standards of buildings like gymnasiums especially well, which typically have a space that is large in height and width and high in heat source density. Therefore, as one form of displacement ventilation, gymnasium building under-floor air supply system has been gaining increasing usage in gymnasium buildings.In our research, we first calculate the air-conditioning load in the contest hall using the traditional stratified air conditioning load calculation method for large spaces. Subsequently, we design the air distribution scheme of the under-floor air supply system and determine the operation conditions and simulation scheme as well, according to the importance of the system parameters that influence human thermal comfort level (HTCL). Following the simulation scheme, we simulate two air inlet shapes, circular straight blade diffusers and swirl diffusers, by iterating all the possible operation conditions. The simulations are performed by applyingκ～εtwo-equation turbulence model using FLUENT, widely used computational hydrodynamics software for air distribution simulation and analysis in the HVAC industry. Based on the result of each simulation, we analyze the pattern of temperature and air flow velocity distributions in the flow field. Through comparing and contrasting the simulation results of different operation conditions and analyzing HTCL using Air Diffusion Performance Index (ADPI), we work out a relatively optimal scheme of under-floor air supply system:circular straight blade diffusers with air speed of 0.3 m/s and supply air temperature difference of 4.5℃; swirl diffusers with air speed of 0.6 m/s and supply air temperature difference of 5℃. The different results generated by using the two air inlet shapes indicate that swirl diffusers outperform circular diffusers in implementing large volume air supply with small temperature difference because the speed of the air emitted from swirl diffusers attenuates rapidly. This advantage of swirl diffusers allows using fewer diffusers with even smaller size to achieve the same air conditioning effect. Also, as under-floor air supply systems have issues with not providing sufficient cooling for the back seats on the upper floor, we then revise the simulation by including local metal chilled ceiling panels. The results of the revised simulation demonstrate that the most desirable air conditioning effect is achieved by the utilization of an under-floor air supply system with local metal chilled ceiling panels in the air distribution system in the contest hall of a gymnasium. The potential value of this combination warrants future research and presents a possibility of popularization.