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The report express some thoughts about the influence of the air distribution on droplet infection and airborne cross infection. The text is based on full-scale experiments with tracer gas and numerical simulation.First: what is the difference between droplet infection and airborne infection?

At present mixing ventilation is mostly used in practice. Although it has been applied for many years the conditions for its optimal performance in practice are not widely understood. A new REHVA design guide book is giving an overview of the nature of mixing ventilation, design methods and its evaluation under laboratory conditions and in practice.

We protect ourselves from airborne cross-infection in our indoor environment by supplying fresh air to the room by natural or mechanical ventilation. The air is distributed in the room according to different principles as e.g. mixing ventilation, downward ventilation, displacement ventilation, etc. A large amount of air is supplied to the room to ensure dilution of airborne infection.The paper discusses both the macroenvironment and the microenvironment. The macroenvironment is the conditions created by the air distribution system, and the microenvironment is the conditions created by the local flow around persons in combination with the surrounding conditions.Analyses of the flow in the room (macroenvironment) show a number of parameters that play an important role in minimising of airborne cross-infection. The air flow rate to the room must be high, and the air distribution pattern can be designed to have high ventilation effectiveness. Furthermore, personalized ventilation may reduce the risk of cross-infection. Personalized ventilation can be used especially in hospital wards, aircraft cabins and, in general, where people are located at defined positions.Analyses of the flow in the microenvironment show that a number of variables are important, as e.g. distance between people, people’s posture, surrounding temperature gradients and surrounding temperature, activity level, etc.Experiments with tracer gas simulating droplet nuclei and experiments with large particles, simulating droplets are used for the study of airborne cross-infection risk and for the study of dropletborne transmission of a disease. CFD predictions are used to support these experiments.

This final report for the Hybrid Ventilation Centre at Aalborg University describes the activities and research achievement in the project period from August 2001 to August 2006. The report summarises the work performed and the results achieved with reference to articles and reports published in the period.

The aim of the ventilation system is to control cross infection in an aircraft cabin if one or a number of the passengers are “source patients” (source of airborne disease). The Personalized Ventilation described in this text is of the type mentioned in “Free Convection Personalized Ventilation”.

The paper shows detailed measurements of the air distribution in a room ventilated by mixing ventilation according to the specifications given by the International Energy Agency work. (Energy Conservation in Buildings and Community Systems Programme, Annex 20). It describes a number of flow elements and how they are used as design tools. The flow elements are the throw of an isothermal jet and the change in jet velocity when the jet moves from the upper to the lower part of the room. A third flow element is the penetration length of a non-isothermal wall jet. The paper shows detailed measurements of the air distribution in a room ventilated by mixing ventilation according to the specifications given by the International Energy Agency work. (Energy Conservation in Buildings and Community Systems Programme, Annex 20). It describes a number of flow elements and how they are used as design tools. The flow elements are the throw of an isothermal jet and the change in jet velocity when the jet moves from the upper to the lower part of the room. A third flow element is the penetration length of a non-isothermal wall jet.

This paper describes the results of laboratory measurements of the airflow from a bottom hung window mounted near the ceiling of a ventilated room. In the laboratory set-up it was possible to control the temperature difference and the airflow rate through the window. The pressure drop through the window was measured as well as the velocity distribution in the incoming airflow. Airflow patterns and penetration depth of a cold jet were studied with smoke visualisation.

The research on air distribution in rooms is often done as full-size investigations, scale-model investigations or by Computational Fluid Dynamics (CFD). New activities have taken place within all three areas and this paper draws comparisons between the different methods. The outcome of the lEA sponsored research "Air Flow Pattern within Buildings" is used for comparisons in some parts of the paper because various types of experiments and many countries are involved.

In the summer 1988 13 countries under the International Energy Agency established a cooperative work - Annex 20. This Annex is divided into two subgroups where Denmark contributes in subtask 1. This contribution is giving a historical background for the establishment and the contents of Annex 20. The purpose of Annex 20 is to carry out simulations and full-scale experiments and to compare these investigations. This is done to support a more common use of advanced numerical calculations in engineering flow calculations within the field of ventilation. In the project it is possible for the countries to make investigations which are of particular interest for them in order to increase the understanding of the complicated flow patterns in ventilated buildings.

A number of different models on the air distribution in rooms are introduced. This includes the throw model, a model on penetration length of a cold wall jet and a model for maximum velocity in the dimensioning of an air distribution system in highly loaded rooms and shows that the amount of heat removed from the room at constant penetration length is proportional to the cube of the velocities in the occupied zone. It is also shown that a large number of diffusers increases the amount of heat which may be removed without affecting the thermal conditions. Control strategies for dual duct and single duct systems are given and the paper is concluded by mentioning a computer-based prediction method which gives the velocity and temperature distribution in the whole room.

The air supply openings in ventilated rooms are often placed close to the ceiling. A recirculating flow is generated in the room, and the region between the ceiling and the occupied zone serves as an entrainment and velocity decay area for the wall jets. Ceiling-mounted obstacles may disturb this flow and, in particular, certain dimensions and positions of the obstacles cause a downward deflection of the jets into the occupied zone resulting in reduced thermal comfort for the inhabitants.

An important element in the natural ventilation design procedure is the flow-pressure characteristics of a window with a -given opening area. The flow in the room is another important element that is often ignored in the design phase due to lack of relevant information on the air movement. This paper shows the outcome of experiments with the room air distribution. The results show that the velocity distribution in the occupied zone can be described by a semiempirical model.