Application of ventilation techniques, as well as the use of any passive environmental solution in a rehabilitation, requires knowledge of the particularities of the climate and the specific characteristics of the building stock. In a theoretical approach, these two variables would be enough to predict indoor behaviour. Nevertheless, in practice, one third variable needs to be considered, as user habits can completely change the equation.

Currently, various studies have demonstrated some doubt about the accuracy of the orifice equation when applied to the calculation of cross-ventilation. As a result, a computational fluid dynamic (CFD) simulation is considered the best method of analyzing cross-ventilation properties under present conditions. However, repetition of CFD analysis to determine the optimum ventilation performance is particularly complex. Accordingly, a flow network model that corresponds to cross-ventilation was developed and suggested as a more efficient means of determining the optimal opening conditions.

This paper presents the results of a field study conducted on 31 houses owned by a French social housing management body. The central objective of our investigation was to propose and evaluate rehabilitation scenarios to improve the envelope airtightness. For this, pre- and post- envelope leakage measurements were performed together with infrared thermography analyses. In parallel, the occupants were interviewed to better understand their interaction with the thermal functions and what their feeling was about the thermal comfort and indoor quality in their homes.

Introduced for the first time at 25th AIVC Conference in Prague in September 2004, the HR-Ventproject still delivers new rich teachings since its start in January 2004. Until December 2005, morethan 700 million data have been recorded on 180 extract units in 5 occupied collective buildingslocated in NANGIS (France).

A hybrid ventilation system controlled by a pressure difference sensor was installed on a detached test house. Performance of this ventilation system was evaluated through the field measurement taken into account the different conditions of the air supply and the exhaust systems. The results of the measurement revealed that the exhaust airflow rate was relatively stable while the indoor-outdoor temperature difference varied and the wind velocity changed. The exhaust airflow rate met the target airflow rate of 64% during the whole measuring period.

The impact of the urban environment on natural and hybrid ventilation was investigated through experimental and computational procedures in the framework of RESHYVENT European Project. An experimental campaign was organized in two urban street canyons in Athens, during summer 2002, consisting of field and indoor experiments. The experiments aimed at the investigation of the impact of the various urban features on the efficiency of different ventilation systems.

According to the R&D Project on Low Energy Housing with Validated Efficiency, the CO2 emissions due to operation of ventilation systems are estimated to be 7 to 12% of total CO2 emissions of a unit of multi-family buildings in mild climate regions of Japan. Using network model calculations, CO2 emissions of a hybrid ventilation system using Natural Ventilation Openings and other ventilation systems were estimated.

In the recent past, residential buildings in temperate climates were ventilated by the daily opening of windows and by exaggerated window and door permeability. Energy conservation concerns have led to better quality windows and lower air permeability that consequently increased the risk of condensation whilst decreasing indoor air quality. Because of the variation in natural factors, such as wind speed and the stack effect, natural ventilation systems are unlikely to permanently provide ideal ventilation rates.

Cross ventilation is one of the most important techniques for achieving energy conservation and for maintaining a comfortable indoor environment in summer. But it is difficult to evaluate the effect of cross ventilation quantitatively and to design based on a quantitative evaluation, because the indoor environment is uneven and changes with the outside conditions under cross ventilation. The full-scale model experiment has been done under cross ventilation, and the properties of airflow in and around the full-scale model have been examined.

Direct and indirect measuring techniques are available for determination of ventilation rate in naturally ventilated buildings. Direct measuring methods include measuring fan, propeller gauge, hot wire anemometer, particle image velocimetry, laser Doppler anemometer, and transit time sonic anemometer. Basic disadvantage of direct measuring techniques is that they are generally used for point or local measurements of air velocity.