Numerical Study of the Return Air Characteristics in the Stratified Air-Conditioning System with Middle Sidewall Air Return Intakes

Abstract

For energy efficiency and better IAQ, stratified air distribution (STRAD) systems with low sidewall air supply (LSAS) and middle sidewall air return (MSAR) are even more used nowadays in large-space buildings. Located between the air-conditioning zone (ACZ) and non-air-conditioning zone (NACZ), the air return opening will intake air flow from both sides. In order to study the air flow characteristics near the air return opening computational fluid dynamic (CFD) is used. CFD physical model is built in accordance with the dimension of the reduced-scale model. A steady-state simulation is conducted first for the calculation of the steady temperature and velocity field, and then, the air in ACZ and NACZ is marked separately with the ‘Same Property and Different Name’ method which is although the gas in both zones has different names, they share the same physical property with the normal air. After that, transient simulation with species transport equations continues to simulate and log the fraction of species in the air return flow. By evaluating the fraction of the species within return air flow, the proportion of return air from NACZ and ACZ can be calculated. By further processing the temperature and cooling capacity of each zone can also be demonstrated. These above mentioned can provide reference to the calculation of the total heat transferred from the NACZ to the ACZ which is critical to the cooling load of a large-space building.