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.

This project aims to demonstrate via a refurbishing operation, how a mechanical ventilation system can both provide a good indoor air quality and limit the energy consumption due to air renewal. The field of this operation concerns the improvement of indoor air quality for sensitive people as young children in classrooms, associated to a rational use of energy by the ventilation systems.

The present paper presents the results of the energy and environmental evaluation of ten school buildings in the Greater Athens Area. The research included measurements of the indoor air quality, evaluation of the situation of the building envelope, recording of energy and ventilation systems and generally all the systems that influence the energy output of the school buildings. Experimental investigations were performed in ten different schools and the concentration levels of CO2, CO and VOCs were measured.

Ventilation in buildings is necessary first for hygienic reasons and also to preserve the building structure. This is more essential, today, because the buildings are more and more airtight, mainly due to energy regulations. It is also evident that air renewal energy losses and fan consumption become more and more important in relation with the total energy consumption of buildings. Nevertheless, many defaults are encountered on installed ventilation systems. It seems necessary to check the installations, at the starting up and regularly in time, and not only when the problems occur.

Industry-wide methods of assessing duct leakage are based on duct pressurization tests, and focus on highpressure ducts. Even though low pressure ducts can be a large fraction of the system and tend to be leaky, few guidelines or construction specifications require testing these ducts. We report here on the measured leakage flows from ten large commercial duct systems at operating conditions: three had low leakage (less than 5% of duct inlet flow), and seven had substantial leakage (9 to 26%).

The increasing concern on energy conservation in buildings and the increasing insulation level of buildings, lead to the introduction of limits for building airtightness, to minimize building heat losses. In some countries the recommended limits are very strict and could be difficult achieved with standard construction practices. Usually the limits are established according construction (best) practices and in some countries it takes in account the building type, ventilation system and weather. Usually those limits dont take in account the air flow rate for background ventilation.

Studies on buildings’ airtightness have shown that several issues can arise from uncontrolled airflow leakages in buildings (e.g., higher energy cost, thermal comfort and health of occupants, building components and equipment preservation). The new French

In 1998, Persily published a review of commercial and institutional building airtightness data that found significant levels of air leakage and debunked the myth of the airtight commercial building. This paper updates the earlier analysis for the United States by including data from over 100 additional buildings. The average airtightness of 28.4 m3/hm2 at 75 Pa is essentially the same as reported by Persily in 1998. This average airtightness is in the same range as that reported for typical U.S.