air flow

Describes a project which attempted to match simulated and measured tracer gas test results and to determine how much effort is necessary to produce sufficiently accurate results. The research assessed the overall value of CONTAM96 as a representative example of available simulation-model programs from both technical and practical viewpoints.

Part 1 of this feature discussed the particular moisture and air quality related problems of midrise housing, and took a close look at two cases. This article analyses issues unique to 'Veterans Era Housing' (US housing built for World War II veterans during the 40s and 50s) and presents three cases where moisture problems were successfully addressed.

States that an air filter can prevent sources of infection entering the ventilation system. It keeps the ventilation system in good condition, and maintains the air flow rate, the temperature and the RH for which is has been designed. It also keeps the efficiency of the heat exchangers at a high level. The same areas of attention should apply to both the return system and the supply system.

The aim is to develop a new method for comfort in settings with high thermal load in buildings that do not require continuous cooling but cooling only during shorter periods. Example of such buildings is schools. The present ventilation and control systems are designed for supply of air at a constant flowrate or to respond to relatively slow variations in load or step changes in load. The slow variations in load are mainly governed by the diurnal cycle and sudden step changes in load are mainly due to people entering or leaving a room.

In this study a parametric analysis was carried out of the interaction between louvres and various perforated mesh screens. This type of arrangement is common in through-the-wall ventilators used for natural ventilation in buildings. An airflow testing rig was used to examine the impact on louvre airflow performance of the meshes. The interaction of louvre geometries and blade inclinations with meshes of different hole sizes was also investigated experimentally.

The paper reviewed the supply opening models of describing inlet boundary conditions for indoor airflow simulation firstly. Then examples of isothermal free air jets from a grille are presented to validate full representation of supply openings. Some results by the simplified method called N-point supply opening model, are also shown to compare with the full representation method. Four different outlet conditions of a grille are studied. The k-e turbulence model is applied.

Describes the use of a two-layer model to predict mixed convection. It uses a one-equation model for near-wall region and the standard k-e model for the outer-wall region. In six cases its validation shows good agreement between computed and measured data. The model also reduces computing costs.

Describes a simplified numerical model, POMA (Pressurized zOnal Model with Air-diffuser, intended to predict the airflow pattern and thermal distributions within a room. The authors introduced jet characteristic equations into the model to make its application general for mechanically ventilated buildings. The models prediction was compared with experimental results and with that of another zonal model and a CFD model. Both natural and forced ventilation were considered. States that the findings show that the POMA model is a practical tool for ventilation system design.

States that there are problems involved with the use of traditional instruments such as vane anemometers and pitot tubes when measuring airflow rates in HVAC systems in order to balance air distribution. Suggests that the simple and useful tracer gas techniques that are commonly used for ventilation measurements in buildings can be a suitable alternative. Describes a preliminary study intended to determine the viability and accuracy of the tracer gas technique. A good correlation between the airflow rates measured by using a pitot tube and tracer technique was found.

When designing the outlets for the ventilation or hot-air heating of particular spaces, we meet usually the problems to specify a form and reach of the air jet and a distribution of velocities and temperatures in the space followed. In practice the calculations of nonisothermal air jets are made using a number of calculation relations to be found e.g. in lit. (1) and other. But when applying the analogical relations derived by different authors we can find out considerable differences in results.