air distribution

Zonal models are often used in analytical calculation of temperature, concentration or humidity conditions in ventilated spaces. The space is divided in two or several zones ( 1 ). The zoning of the space is based on the assumption of constant temperature,  concentration and humidity in each separate zone. The balances for air mass flow, contaminant mass flow, water vapour mass flow and heat flow are determined between zones and between zone and outer boundaries.

This paper discusses the application of a new strategy approach for the room air conditioning. The basis of the classification is different aims or ideas of the temperature, gas, particle, humidity distributions and room air flow patterns that can be created within a room. A certain strategy can be applied by using different system combinations of room air distribution, exhaust, heating and cooling methods and their control. The realization of an ideal strategy is also dependent on the operating parameters and internal sources.

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 semi empirical model.

For natural ventilation of rooms there is a wide range of possibilities with regard to the selection of window type, size and location. A bottom hung window mounted near the ceiling is often used as it has proved to work well with regard to draught risk and thermal comfort in the room. However, there is a need for more detailed information on the performance of this and other types of windows to make it possible to use improved design methods for natural ventilation systems.

In dwellings ventilated by extract ventilation there are common complaints of cold draught caused by the supply air entering the room through openings close to the windows. This paper reports on studies of unconventional ways to distribute the supply air in order to minimise the risk of such problems. Experiments have been done where the supply air device is located in the hall of an apartment. The ventilation efficiency in the rooms adjacent to the hall has been studied with open and closed doors. The behaviour of gravity currents has also been studied in scale models.

Air leakage and duct wall conduction in forced air distribution systems often waste 20% to 40% of the energy used to condition residences in hot, humid climates. The simulation of these forced air distribution system leakages, their attendant uncontrolled airflows within the building system, and their consequential energy uses may be achieved by treating building spaces as pressure vessels (nodes) that are interconnected with the forced air distribution system, the outdoors, and each other through the basic laws of pressure and airflow.

Computational Fluid Dynamics (CFD) has been used to predict the indoor environment airflow and overall ventilation effectiveness of natural or mechanical air distribution systems. This paper highlights some applications and criticism work made on CFD in order to establish an understanding of the limitations of CFD in predicting room airflow. It is concluded that though CFD is a powerful tool for simulation, the software complexities, computational power and the level of expertise that CFD codes require shape the greatest challenges to beginners in this field.

A large number of modem European buildings are equipped with ducted air distribution systems. To investigate the implications of duct leakage, a field study was performed on 42 duct systems in Belgium and France. The measurement data confirm the findings of the few earlier experimental investigations on these matters in Europe. In our sample, the leakage rate appears to be typically three times greater than the maximum permitted leakage adopted in EUROVENT 2/2 (Class A).