PR2000

At sufficiently high Reynolds numbers, the discharge coefficient Cd associated with a sharplycontracting flow through a square-edged opening is, in general, taken to be constant.

The target in this study was to decrease the energy use for transportation of air (fanenergy) with a factor of three. Two real systems composed of existing componentswere constructed in a laboratory; a mechanical exhaust system and a balanced system.The flow rates through the systems were set at values according to the Dutch BuildingRegulations. This situation is called the reference situation. A number ofimprovements have been tested and studied.

This paper outlines work in progress to develop dissemination material to assist the appropriate application of solar and passive ventilation in urban buildings.

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.

There has been a growing interest in the use of natural ventilation in buildings to supplement orreplace mechanical air supply systems. However, for buildings in busy urban areas the potentialto use natural ventilation can be limited by excessive noise entering through natural ventilationopenings such as windows and trickle ventilators. Such openings tend to have large open areasto enhance air flow while offering a very low resistance to the transmission of external urbannoise.

In 1998 the Dutch ventilation industry launched a new generation of domestic ventilation systems on the market with high efficiency heat recovery applying counter flow heat exchangers and DC fans. It is expected that these ventilation systems will play an important role in realising the goals of the Dutch national energy policy for reducing energy use in the built environment. Another important aspect is the contribution to a healthy indoor environment in dwellings with an extreme high energy efficiency, especially in relation to increasing air tightness and thermal insulation.

In order to assess the real performances of different demand controlled ventilation (DCV)systems, two of them were installed in meeting rooms of an office building.The first system is controlled by movement detection on terminal units and has been installedin a small meeting room which is regularly used.The second system is controlled by CO2 detection and frequency variation on fan. It has beeninstalled in a large meeting room (30 persons seated, up to 50 persons standing).The systems have proved to be energy saving with correct CO2 levels.

A hybrid ventilation system is a two-mode system that can automatically switch between passive and mechanical mode at different times of the day or seasons of the year. Some ventilation systems, including the hybrid system, have been set up in a full-scale test house constructed in Tohoku University, Japan to assess their performance. In this paper, the performance of each system is described by giving measurement results.

Ventilation needs in dwellings must be determined on the basis of both requirements to theindoor air quality and necessary control of moisture conditions. As a first step towardsdevelopment of energy efficient ventilation strategies for demand controlled ventilation infuture dwellings theoretical analyses comprising a literature study and mathematicalsimulations have been carried out.

Knowledge and estimation of the wind speed and air flow characteristics, in a city, is of vitalimportance for passive cooling applications and especially in the design of naturallyventilated buildings. This study is referred to the analysis of the wind characteristics in urbancanyons as a function of the free stream wind. The impact on the airflow rate calculation isdiscussed for an urban canyon. The goal of this study is to get a better insight of the impact ofthe urban environment on the ventilation effectiveness.