Analysis of the Thermal Performance and Comfort Conditions of Vernacular Rammed Earth Architecture From Southern Portugal

Abstract

From the beginning, humans had to look for shelters to protect themselves from other animals and the climatic elements. But it was in the Neolithic, when humans moved from a nomadic to a sedentary life, that they decided to build permanent shelters. These shelters evolved over thousands of years and generations, across the world, and diverse vernacular techniques and forms have been developed and improved to better respond to climate constraints and to provide the best comfort conditions possible. To attain thermal comfort conditions vernacular buildings were built using low-tech passive strategies that take advantage of available endogenous resources and other criteria such as sun exposure, geometry, form, and materials, among others (Coch, 1998; Singh et al., 2011; Fernandes et al., 2015a,b). With the industrialization of the building sector, the vernacular knowledge was often forgotten in building design and its use declined. Moreover, nowadays, buildings too often rely on heating, ventilation, and air conditioning (HVAC) systems to ensure indoor thermal comfort conditions (Fernandes et al., 2015a,b). Thus, the relevance of vernacular features is still valid today in the scope of sustainability, being the basis of what is now defined as sustainable building design (Cardinale et al., 2013). Environmental awareness is increasing and underlining the problems related to energy efficiency and environmental impacts in buildings. The building sector is one of the largest energy and natural resources consuming sectors, being responsible for a third of global total CO2 emissions and primary energy use (Ürge-Vorsatz et al., 2015). Therefore, new high-performance building concepts have been defined, such as the “nearly zero-energy buildings” (nZEB). An nZEB is a building with a very high energy performance (due to an improved envelope and use of very efficient HVAC systems) and where the very low energy demand must be covered by energy from renewable energy sources. The awareness of vernacular architecture regarding passive and low energy architecture is increasing, since it is intrinsically related to the local climate, uses passive, low-tech techniques, and is not dependent on nonrenewable energy sources (Kimura, 1994; Singh et al., 2011; Fernandes et al., 2013), which makes these strategies suitable and valuable to achieve the nZEB level in different climate contexts. Several studies have shown that vernacular buildings have a good thermal performance, allowing achieving acceptable thermal comfort levels during most of the year by passive means only, reducing the energy demand for heating and cooling (Martín et al., 2010; Singh et al., 2010; Priya et al., 2012; Cardinale et al., 2013; Fernandes et al., 2015a,b). In Portugal, there are some studies focusing on the passive strategies used in the vernacular building, but there is a lack of results showing the influence of these strategies on the thermal performance of vernacular buildings, namely of rammed earth buildings. Portugal is a relatively small country, but it is a territory full of contrasts. Even though the variation in climatic factors is rather small, they are sufficient to justify significant variations in air temperature and rainfall, as can be seen in Fig. 1, which shows the differences in mean air temperature for mainland Portugal during winter and summer. As Fig. 1 shows, the northern part of the country has cold winter and dry and mild summers, while in the southern part, the winters are mild, and summers are warm and dry. As a response to these differences, Portuguese vernacular architecture developed specific and different strategies in both regions. In the north, these strategies are more oriented to increase heat gains and reduce heat losses during winter, while in the south they are more focused on passive cooling during summer. A more detailed explanation about the characteristics of these vernacular strategies can be seen in the following sections. As vernacular architecture has shown, a building solution/strategy does not fit all contexts. The diversity of vernacular construction systems that exist in Portugal leads to the necessity of understanding the actual performance of these buildings. In this study, the main goal was to measure the hygrothermal parameters that characterize the indoor thermal environment and that affect the heat exchanges in vernacular rammed earth buildings from Southern Portugal.