Experimental and numerical investigation of air distribution in a large air-conditioned space building

Ventilation of large spaces in buildings differs from spaces with a small volume, because of the additional air that needs treating while the majority of it is above the occupied area. An enclosure is considered to be large when the floor-to-ceiling height is more than 5 meters or the volume of the occupied zone is generally small compared to the entire volume. The thermal comfort and indoor air quality, which have a direct impact on occupants' productivity and health, are crucially influenced by the building layout and volume and the design of the air distribution system. Many studies have been carried out to test these two factors, i.e. thermal comfort and indoor air quality, separately in evaluating the performance of ventilation systems. The Air distribution Index ADI combines the evaluation of thermal comfort and indoor air quality and has been used in spaces with standard floor-to-ceiling height. The aim of this study is to test the Air Distribution Index which combines several parameters, such as overall ventilation effectiveness for removing pollutants and for temperature distribution ε̅c, ε̅t percentage of dissatisfied PD and predicted percentage of dissatisfied PPD, to assess the performance of ventilation systems in large spaces. The research involved measurements in an occupied large open plan office (floor-to-ceiling height > 5m), and its occupied zone volume is small compared to the total volume fitted with mixing ventilation MV system to establish its performance characteristics and ability to provide the required conditions for both thermal comfort and air quality. The results from this investigation were used to develop a 3-D CFD model and evaluated it for air temperature, air velocity and CO2 concentration predictions for this large space. The 3-D CFD model was used to compare the performance of two different ventilation systems (Impinging jet IJV and mixing) numerically. The comparison was conducted using two different occupancy capacity loads for summer and winter conditions. The IJV system was found to be better in providing a satisfactory indoor environment at all conditions that have been considered as it showed higher ADI values. Based on these findings, it is concluded that using ADI to assess the effectiveness of different ventilation systems in large enclosures can provide useful information that combines both indoor air quality and thermal comfort. Also, the IJV can be a beneficial air distribution system for use in a large enclosure for achieving thermal comfort and good air quality in the occupied zone and reducing energy consumption.