mixing ventilation

Airborne transmissions take place as a transport of virus or bacteria via the aerosol flow in rooms. The distribution of aerosols tends to be evenly distributed if the flow in the room is fully mixed. The aerosols distribution will be different if the room air is stratified. A vertical temperature distribution may create stratified layers with either lower or higher concentrations of exhalation from the infected person.

Building system engineering can help decrease the risk of being infected by the aerosol which contains virus-laden droplet nuclei. Many techniques can help decrease the concentrations of particles. This paper focuses on the economic renovation of the existing ventilation system of a public commercial space, a small meeting room in Kuijpers, Leiden, to decrease airborne transmission of respiratory infectious diseases.

Experimental investigation of ceiling circular grille air jets was conducted in a full-scale entirely controlled test room (6.2 x 3.1 x 2.5 m). Our case study is based on a realistic ventilation system configuration: it introduces a plenum box, two air exhausts, as well as a vertical wall near the air inlet. Analyses were initially concentrated at the air inlet region since it is the zone having strong gradients. Deviations concerning the trajectory of the actual jet were observed with respect to the theoretical jet.

Bases on the concept of task/ambient ventilation, fresh air can be decoupled from re-circulated air so as to improving ventilation effectiveness in breathing zone. Ceiling mounted high velocity circular jet diffusers, which are regarded as remote personalized ventilation air terminal devices (PV ATDs) without affecting room aesthetic effects, can be utilized to supply fresh air without causing draft rating because tropically acclimatized occupants prefer slightly higher air movement. Under-floor air diffusers are used to supply re-circulated air.

This study developed a drift-flux model for particle movements in turbulent indoor airflows. To account for the process of particle deposition at solid boundaries in the numerical model, a semi-empirical deposition model was adopted in which the sizedependent deposition characteristics were well resolved. After validation against the experimental data, the drift-flux model was used to investigate human exposures to particles in three normally-used ventilation types: mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD).

Air quality in offices depends on the ventilation system ability to remove contaminants from the occupied zone. In a low polluted building air quality mainly depends on the human presence and carbon dioxide is normally used as indicator of human bioeffluents.

Stratum ventilation has been proposed to cope for elevated indoor temperature recommended by governments in East Asia. TRNSYS is used for computation of the space cooling load and system energy consumption. A typical Hong Kong office is investigated. Compared with mixing ventilation and displacement ventilation, stratum ventilation derives its energy saving potential largely from the following two factors: a reduced ventilation load and increased coefficients of performance (COP) for chillers.

The 3DFLOW code has been developed based on:
· The standard three-dimensional K-epsilon two-equation turbulence model;
· A modification for buoyancy effects;
· Wall functions applied to deal with solid boundary conditions;
· An adaptation of the SIMPLE algorithm.
The representative indoor air flows in conditioned spaces, including downward mixing, partition and displacement ventilation cases, were simulated and analysed in detail using the 3DFLOW code. Good agreement was found between the numerical predictions and experimental data.

How to avoid or reduce the influence of suddenly released contaminant when emergency occurs ? A 3D Full scale room with displacement and mixing ventilation system is numerically studied assuming contaminant released at certain positions in the room. IACS is adopted as an index that can be applied to determine ventilation strategy with the aim of defending indoor environment against contamination.

This paper sums up the results of a study on the internal partitioning with its effects on the room air quality along with the ventilation performance. Physical tests and numerical modeling for a CFD simulation were used to evaluate different test conditions that employed mixing ventilation from the ceiling.