The influence of architectural culture on the energetic skills of less developed countries

Transcription

1 The influence of architectural culture on the energetic skills of less developed countries J. A. Mendes da Silva 1 & A. T. Ferreira Ramos 2 1 Department of Civil Engineering, University of Coimbra, Portugal 2 Polytechnic Institute of Castelo Branco, Portugal Abstract According to several international organizations, including the United Nations, the sustainable development is, today, one of the most global concerns of developed countries and an increasing concern of less developed countries. Sustainable construction is a quite important sub-domain within this context. In order to contribute to improve the knowledge and practice in this domain, we have carried out a research program to analyse and to compare the constructive solutions used in two different countries, with quite different climates, that share many cultural and historical influences: Portugal (Europe) and Cape Verde (Africa Atlantic Ocean). We have studied these two countries in terms of climate, history and social and cultural development, in what concerns construction. The buildings and the way of living at these countries were analysed face to face with the ideal passive solar solutions, resulting in the climate characterisation of each country, namely, the severity of Cape Verde arid climate and the Portugal temperate climate. The climate diversity of Cape Verde islands, the colonisation influences, as well as its development and, also, the most natural relation between man and the environment can clearly explain the co-existence of so many constructive solutions. This work contributes to find an architectonic identity compatible with the climate and the local resources. Keywords: sustainable construction, solar passive architecture, vernacular construction, less developed countries, thermal comfort. 1 Introduction The evolution of technology has been responsible for deep changes on architecture principles and it often breaks an old and clear connection between

2 284 The Sustainable City III architecture and climatic local conditions. For example, decreasing initial costs of AVAC systems, simultaneously with their increasing skills on internal comfort guarantee, in spite of their high consumption of energy, encourages the option for different kinds of materials and construction techniques that are, frequently, undesirable according to climatic local conditions. This phenomenon is promoting serious increasing of energy consumption in the housing sector. The respect for the characteristics of the traditional local architecture can be considered as an important guideline in order to reach the way of the sustainable development. The Agenda 21 on the Sustainable Construction [1] defines the respect for the local culture and the traditional construction as an aim to establish the parameters of the sustainable construction and its implementation in the civil engineer industry. 2 Climatic characteristics of Portugal and Cape Verde 2.1 The climate in Portugal and Cape Verde The two countries analysed in this work present climatic features significantly different. Portugal has a temperate climate with great thermal amplitude between the two most important seasons, winter and summer, and the country is divided in three climate zones [2] for each one of them. The summer zones are V1, V2 and V3, and the winter zones are I1, I2 and I3. The zones I3 and V3 are the most severe, respectively, the coldest and the hottest. The figure 1 presents, on the left, the division of Portugal in two maps (corresponding, respectively to winter and summer zones) and shows, on the right, the map of the Cape Verde archipelago, which is constituted by 10 islands, with a total area of 4030 Km 2 and a population of persons (according 2000 national inquiry). Figure 1: Localization of Cape Verde and Portugal.

3 The Sustainable City III 285 The climate of Cape Verde is characterized by its severity. The archipelago is situated in an area of arid climates, and it is located near the African coast (500 km between Boa Vista Island and the coast) and under the desert of Sahara winds influence. The pluvial occurrence is even null in some islands as Sal, Boa Vista and Maio, which present higher temperatures than the others. The atmosphere is more humid at Santo Antão and Brava, because it rains regularly. 3 Portuguese influence in Cape Verde Cape Verde was colonized by Portugal. Firstly, the country was used as a support to the economic and commercial expansion of Portugal due to its geographic position in the crossing of the African routes [3]. In the XVIII century the commerce with the African continent was forbidden and Cape Verde presented an internal economy growth with the development of the local commerce, craftwork and agriculture. However, it was also marked by several aridity periods with repercussions in the agriculture and society (unemployment, companies bankruptcy). The XIX century was characterized by the aridity which provoked the death of animals and, approximately, people. During the XX century, Cape Verde economy was still getting worse. The decrease of the exportation, the lack of investment, the non-existence of renewing techniques, mainly in agriculture, can be considered as the most important factors to this crisis. The land was depleted with the continuous cultivation and the surface decreased due to the erosion and persistent aridity. In 1956 was created the PAIGC (African Political Party of Independence of Guinea and Cape Verde). These two countries had similar histories with the Portuguese administrations and the same ethnical origins (the Cape Verde slaves were carried from Guinea). In 1975 was proclaimed the independence of Cape Verde. The new country crossed great problems as the non-existence of industries, energy sources and the old techniques used in agriculture and fishing. The archipelago received international support to improve the economic sectors of the society and, consequently, improve the life quality, the health and the education (the reduction of illiteracy). However, on the late 90's the poverty ratio was still near 25% and the illiteracy was around 70%. According to the last national inquiry, more than 46% of the population of Cape Verde is living with extremely low comfort conditions and 18% with low comfort conditions. This value is different all over the archipelago: the better situation is observed at Sal Island (with an high tourism activity), with more than 60% of the population living with acceptable comfort conditions. However this island represents only 5,64% of urban population and 0,75% of rural population of the archipelago. At Santiago Island (mainly discussed on this paper) lives more than 50% of the population of the archipelago. There, more than 30% of its population has acceptable comfort conditions and 3,7% reached a very high standard of comfort.

4 286 The Sustainable City III A significant part of the population is living, now, at the main town (Praia) or at its surroundings, what increases the problem of housing. 4 The actual frame of the construction in the islands The constructive reality in the islands is quite variable. The architecture presents European, African and Asiatic influences with different results according to its characteristics and adaptation to the local climatic conditionings. Figure 2 shows some examples of recent European influence in Praia Santiago Island - without any attention to the interior comfort and environmental impact. In this particular region of the world, with extremely climatic features, the exterior spaces assume a preponderant preoccupation to reach the comfort, because of the natural discomfort caused by the low relative humidity. The worst examples of this non-adequate recent European influence are related to some buildings of flats, which represent a reduced, but increasing, parcel of housing solutions in Cape Verde, particularly at the urban centres. Window details Exterior envelope of buildings Glazed surfaces without adequate protection Figure 2: Recent European construction in Cape Verde.

5 The Sustainable City III 287 Some guidelines can be adopted to minimize this issue as the use of natural covers at the ground in outside; the use of vegetation to promote shadowiness and to increase the relative humidity in the air by transpiration and evaporation; the use of solutions that include water to provide the cooling by evaporation. This kind of architecture, design and technical solutions need to be upgraded in order to provide a better thermal performance in the interior and exterior. Figure 3 shows some examples of buildings at Praia town, where it was made a really effort to conciliate architectural options and the external solar protection. A brief analysis of the old colonial Portuguese architecture (fig. 4) shows that some of these rules - concerning solar protection and adequate natural ventilation - were included in housing design. This, absolutely, doesn't mean that we can (or even that we should) copy these architectural solutions for today, but it shows, clearly, that it is possible - with any kind of cultural principles that can support a constructive identity in Cape Verde - to find an adequate climatic approach to the construction. The control of some parameters (i.e. air quality, temperatures, relative humidity), as shown by Figures 3 and 4, can provide guidelines to the architectural design and construction under a sustainable work platform. Double envelope providing shadowiness Constructive elements to control the solar incidence Horizontal shadowiness elements Figure 3: Examples of architectural climatic approach in Cape Verde.

6 288 The Sustainable City III Roof detail which allows a way out for warm air Windows external protection, allowing diffuse lighting and ventilation Massive construction, using light colours Figure 4: Some examples of colonial Portuguese architecture. Part of this analysis - carried out in order to contribute to find a constructive identity in Cape Verde that can respect climatic factors under a sustainable point of view - consists on understanding the vernacular architecture and its relation with the local resources and climate, the key to all the process. Some examples are shown in Figure 5 (top rows). Recent architectural experiences have been made, namely at Cidade Velha, to test improved old construction techniques to reach the new standards of comfort and durability. The management of the urban development is also important in order to prevent an urban uncontrolled sprawl. The quicker expansion of the urban areas due to a social or economic crisis will provoke an existence of poorer zones around the town. This phenomenon contributes to overcharge the existent systems, as infrastructures and transports. Figure 5 (bottom rows) shows the urban periphery in Praia Santiago Island- where a characteristic kind of selfconstruction grows without the minimal safety, comfort or health conditions. As it was said above, 50% of the Cape Verde population lives in this island.

7 The Sustainable City III 289 Vernacular architecture Roof detail with natural thermal insulation Religious architecture (Portuguese influence) Poor urban settlement Popular construction of poorest families Figure 5: Vernacular architecture and poor urban settlement in Santiago Island.

8 290 The Sustainable City III 5 The climate and the passive solar solutions The different climates and necessity of use of passive solar systems were analysed through the application of the Analysis Bio 2.0, software developed by the University of Santa Catarina Brazil. The work methodology consists in over putting the climate data in the psicrometric diagram to calculate the percentage of the time of the year in which thermal discomfort or comfort occur and the percentages in which each strategy is more appropriate. The Figure 6 concerns Sal and São Vicente islands (Cape Verde) and Castelo Branco (Portugal) [4] and compares the results in terms of the discomfort hours per year. These results allow concluding that the ideal use of passive solar techniques is very different in the two countries analysed. It empathizes, also, what passive construction tools are more adequate for each country and zone. Similar results were only reached with the use of passive solar heating and thermal mass, that are passive solar techniques applied to supply the discomfort zones between ten and twenty degrees Celsius (a common condition in Portugal and these islands of Cape Verde). However the choice of constructive solutions should have in mind many others factors as the social, cultural and economic parameters, and the remaining discomfort zones, which present great differences [5]. a b c d e f g h Passive solar heating X X Thermal mass X X X Ventilation X X X Cooling by evaporation X Cooling by thermal mass X Air conditioning X Artificial heating X Figure 6: Comparison between the use and efficiency of the passive solar techniques in three different situations.

9 6 The sustainable construction challenge Cape Verde is working to find its own way to answer to the sustainable construction challenge, supported by the discussion and research about past and present architectural experiences. This work tries to help on this hard task, criticising some of external influences observed at the urban centre of Praia, underlying the best contributions to a passive approach, observed not only on the vernacular housing, but also on old colonial construction and on several modern public buildings. Sustainable construction is defined in The Agenda 21 on Sustainable Construction [1] as The creation and responsible management of a healthy built environment based on resource efficient and ecological principles. Each country should adjust this definition to its local reality, adopting priorities according to their needs. These guidelines must approach the management and organization between the agents of the construction process, the product and building features through their behaviour, consume of the resources and the construction impact in the urban sustainable development. The respect by the local culture and resources, in face of the available technologic evolution, are the mainly items in this way. The construction industry and built environment are responsible for great impacts on the economic and social life of our society. The influence level made of this sector a mainly aim to control the consumption of the resources and amount of the hazardous emissions. The life cycle of buildings and products should be longer to preserve the sources involved in the process. Built environment needs conditions that can be adapted to new demands and functions. The sustainable construction embodies a recent building reality in which the constructions present spaces more functional, with flexibility and adaptability. At last, it is important to remember the main domains of concern to allow a sustainable approach to construction, which are, unfortunately, quite far from decision making process in several countries: energy savings, transport systems the use of renewable energy, water consumption, management of water supply, recycling, use of renewable materials, control of the use of resources, use of land, life cycle of buildings and products, control of the urban sprawl, opportunities in cities, social, economic and cultural aspects. 7 Conclusions The Sustainable City III 291 This paper was divided in four specific stages: Geographic localization and climatic characteristics; Cultural influences; Brief characterization of the constructive and architectural frame; Guidelines to the sustainable construction. This organisation was adopted in order to provide the guidelines to break through on sustainable construction. One of the most important aspects is the

10 292 The Sustainable City III respect by the local culture and the use of techniques based on the local resources. The fact of applying architectural style and design of other countries is quite inefficient in order to implement buildings out of context which will increase the impacts and the negative effects in the interior and, also, in the exterior. Each country needs to find its identity in this new constructive frame and assume this reality as an advantage to the evolution of architecture and engineering. The architecture aspects aware of the climatic characteristics, and the necessity to implement them, will improve the energetic skills in countries with profound needs. Cape Verde can built its constructive identity through the following aspects: the non use of air conditioning, except where passive solutions are insufficient to control the temperature and the humidity inside the buildings; the use of adequate ventilation with suitable techniques; the selection of the most accurate passive solar systems and materials, based on the most successful experiences (vernacular, colonial or modern architecture), namely, through the use of thermal mass and adequate solar protection; the choice of constructive solutions according to the stage of technological development; the respect for the economic and social needs; and, finally, through a profound understanding of the local culture and social organization. References [1] CIB, Agenda 21 on Sustainable Construction, CIB Report Publication 237, Netherlands, [2] RCCTE - Regulamento das características de comportamento térmico dos edifícios (Portuguese thermal code). Decreto-Lei n.º 40/90, Lisboa, [3] Sorgial, Pierre, Guia das ilhas de Cabo Verde; LIDEL - Edições Técnicas, Lda: Lisboa, [4] Ramos, Ana T., Análise do RCCTE face à utilização de sistemas solares passivos em edifícios de habitação, Tese de Mestrado, Universidade de Coimbra: Coimbra, [5] Ramos, Ana T., Silva, J. A. R. Mendes, Análise da Construção Solar Passiva Adaptada a Cabo Verde, Conference at Instituto Piaget: Praia Ilha de Santiago Cabo Verde, 2003.