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Natural ventilation as a part of a buildinǵs function that has a strong effect on human comfort. The reduction of natural ventilation and infiltration, as a part of the ventilation system in the old existing buildings, due to intervention actions, have been causing a reduction in indoor air quality and an increment of relative humidity levels in the indoor environment. Providing optimal indoor condition is not only related to the renewal of the air but also with its distribution. Hence airflow patterns in historical buildings influence interior comfort conditions. The aim of this work is to assess the effectiveness of the existing natural ventilation system in the old and historical buildings by different natural ventilation strategies. To achieve the proposed objective, the research was developed resorting to in-situ measurements and simulation methods The simulation was performed with the Design-Builder software and the main goal was answering to the following question: - What are the existing conditions of the building in concern of the airflow circulation and distribution? The in-situ measurements were performed using Blower Door Test method in order to determine the existing building airtightness. Based on the obtained results for each building the intention is answering the following question: - Due to the limitation of the historical urban areas, which natural ventilation strategy is more effective? The results of this research can be interesting for architects, engineers, and people, who are working on intervention and renovation of old existing buildings.

It is currently recognized that the residential building sector is one of the largest energy consumers in the world. The energy crisis of the 1970s was important for drawing attention to the subject of energy consumption and the necessity to save energy. The airtightness of buildings is an important factor affecting a building’s energy consumption and also energy-saving potential. On the other hand, the ventilation rate has also a significant effect on indoor air quality and is assumed to be an essential criterion of a building’s performance. However, most of the existing research in this area has been developed in cold climates and there is a research gap with regard to countries in warmer climates such as those close to the Mediterranean Sea. Therefore, this research aimed to study the airtightness and ventilation rate of existing buildings by employing in-situ measurements. In-situ measurements were achieved using the fan pressurization test (Blower Door Test) method. According to the selected case studies, the results of the measurements indicate a correlation between building typology, airtightness, and ventilation rate.

The constructive particularities of Portuguese old buildings, with specific and ancient constructive solutions and buildings’ aesthetics, determine the type of interventions and turn some of the most efficient interventions impossible to apply. Since the external appearance of buildings in old city centers must be preserved, nor is the use of external isolation not an alternative, neither the use of materials with low hygro-scopicity, due to the nature of the material used in exterior walls, usually stone. Presented research was expanded to figure out the reaction of different intervention solutions which are used in old buildings’ envelope to accomplish their energy performance. The old city center of Coimbra has a building typology very characteristic and similar to other Old Portuguese city centers, so the idea was to create a representative building of their dimensional characteristics. The modeled building unit was designed after studying around thirty buildings. With all the collected data, it was possible to design a building which we consider that as representative of Coimbra City Centre buildings. This modelled building was used to simulate, with Design Builder software, in real condition and with different solutions for interventions in facades, to predicting the thermal performance achieved for each one. Their final performance was analyzed and compared. The achieved results will be used to define the most suitable interventions in old buildings to improve its energy performance beside of good indoor air quality.

Building airtightness assumes an important role in the energy saving and the indoor thermal comfort. Ventilation rates bring significant impacts on energy usage in the constructions and indoor contaminant concentrations and also setting them as the key parameters in building performance. Ventilation rate have been measured in building for a long time, and there are some developed measurement methodologies related to it in the research domains. However, most of the investigations in recent years have been done usually in the cold climate conditions, while Mediterranean construction are not deeply investigated in the literature. In this paper, the authors present the obtained results of an experimental research which is carried out on the Portuguese residential buildings. The investigation is done by fan pressurization methods, also known as “Blower Door Test (BDT)” as the measurement method as well as Design Builder (DB) as the simulation software. The airtightness measurement of the existing buildings and the influence of air leakage on energy consumption and indoor comfort in different Portuguese construction typologies are focused on the aim of the research. The important parameters of the building such as whole-building air change rates, building infiltration rates, and ventilation effectiveness rate in the residential building are also considered in this research.

A taxa de renovação de ar de um edifício desempenha um papel importante na eficiência energética e no conforto térmico interior dos edifícios. Diferentes características do edifício como idade, altura, localização e tipologia têm influência direta ou indireta sobre a taxa de renovação. Existem já diversos estudos desenvolvidos, neste campo, nos EUA e no norte da Europa, especialmente sob condições climáticas frias, mas os edifícios do Mediterrâneo não têm sido alvo de muita atenção. Assim, este trabalho pretende apresentar uma investigação realizada sobre a correlação entre a taxa de renovação de ar de um edifício e a sua tipologia e altura, em Portugal. Blower Door Test (BDT) foi o método selecionado como metodologia de estudo. Com este objetivo foram efetuadas medições in-situ em edifícios residenciais no Centro Histórico da cidade de Coimbra, Portugal. Os resultados obtidos foram comparados com os valores permitidos na regulamentação Portuguesa. Finalmente e com base nos resultados experimentais e da regulamentação algumas conclusões foram puderam ser retiradas: -Existe uma relação linear entre a altura dos edifícios e a taxa de infiltração. -A taxa de renovação de ar de um edifício multifamiliar é superior de um edifício unifamiliar.