Sistemas de Ventilação Natural e Mistos em Edifícios de Habitação

Abstract

Air quality inside buildings has been a human concern for centuries. Nevertheless, the increased permanence within buildings (approximately 90% of our lives take place indoors) and new building practices, which generate potential hygrothermal deficiencies, have motivated increase interest in this area. The publication of recent Portuguese regulations regarding heating in buildings and air quality has increased the standard regarding hygrothermal behaviour in buildings and the conditions of indoor ventilation. Most residential dwellings in Portugal use a mixed ventilation system (mechanical ventilation in the kitchen and natural ventilation in the bathroom). The potential problems this system presents, namely its intermittent nature and the possibility of reverse flow in the natural ventilation conduits) led to this work. Its main purpose is to measure the performance of a mixed ventilation system and to propose practical recommendations. The vast experimental campaign carried out accomplished a variety of actions in the study of the hourly renewal rates of the proposed ventilation system, namely the experimental characterization of the devices used in the ventilation system trialed and the application of the tracer gas method, with a special emphasis on the PFT technique. The experimental work made it possible to define ventilation demands adapted to the real indoor climate conditions of Portuguese buildings and to establish clear rules that must be followed in a ventilation plan so as to meet those demands. Key words: Ventilation; Dwelling; Air Change Rate (ACH); Tracer Gas; PFT Technique; Decay Technique; Mixed Ventilation System.