Research’s background: the Global Context

Since the Industrial Revolution that occurred during the eighteenth and nineteenth centuries, and the onset of Globalisation, the world has experienced numerous significant changes and major turning points that were fundamental in shaping the contemporary built environment and which have contributed to creating the environmental and energy challenges that we are facing today.

The rapid world urbanisation and vast migration from rural to urban areas that were driven by the economic growth during the last centuries, as well as the changes in development trends, have produced variation in the urban tissue. Consequently, various climate changes have become manifest (Schiller et al. 2006; Calthorpe 2011). This is can be clearly observed in today’s mega cities, and in particular in densely built-up areas, where the typologies of buildings with varying heights and dimensions, as well as the large surface area of urban structure compared to rural, display high thermal mass in their surrounding environments (Arnfield and Herbert 1999; Oke 2002). In 2007, in their Fourth United Nation Report, the Inter-governmental Panel on Climate Change (IPCC) points out that the global mean surface-air temperatures have risen by 0.74°C ± 0.18°C based on a linear trend over the last 100 years, from 1906 to 2005 (IPCC 2007), Figure 1.1. The same report indicates that the rate of warming over the last 50 years was almost double that observed over the whole last 100 years, at 0.13°C ±0.03°C and 0.07°C ±0.02°C per decade, respectively.

Figure 1.1. Annual global mean temperatures observed during the period from 1850 to 2005, source: IPCC (2007)

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Indeed, these increased rates in surface-air temperature has been found, in addition to contributing to discomfort in urban spaces, to further reduce the habitability of urban and sub-urban areas in a number of ways, including; increased pollution, health problems, and even an increase in mortality rates (Changnon et al. 1996; Rosenfeld et al. 1998; Akbari and Konopacki 2004). In addition to the adverse impact caused by warming on the well-being of inhabitants, these rises in urban air temperature can be associated with increasing energy demands in urban buildings. The International Energy Agency (IEA) indicates in their energy report that the percentage of the total energy use in non-industrial buildings, i.e. residential, schools, hospitals and offices, ranges between 30% and 50% (IEA 2008). While, the same report states that the potential energy saving of 20 - 60% in residential space heating and air conditioning could be achieved with the adoption of sustainable strategies, such as the use of new technology. As the world’s urban population has already surpassed the number living in rural areas for the first time (UN 2009), the interest in mitigating the adverse impacts of urbanisation has grown with the increased heat stress in cities and high energy demands from urban dwellers.

The relationship between the built environment and microclimate condition has been widely investigated since the first attempts by Luke (1818) who studied the artificial excess of heat in London compared to various places in the UK (e.g. Oke 1973; Roth et al. 1989; Rosenfeld et al. 1998; Saaroni et al. 2000; Golden 2004; Unger et al. 2010; Pichierri et al. 2012). Most of the literature dedicated to the investigation of urban microclimate has concluded that the alteration in urban microclimate and the elevated air temperature in urban areas, or the so- called Urban Heat Island phenomenon (UHI), are to large extent formed by a number of man-made causative factors, including (a) the urban geometries, (b) the thermal properties of urban surfaces, and (c) the heat released from anthropogenic sources (Oke 2002; Gartland 2008; Rizwan et al. 2008). As there is an increasing belief in the importance of the role of external microclimate conditions in promoting sustainable built environment, the evaluation of the environmental quality and comfort in outdoor spaces has become the central issue in most of the recent scientific conferences that have been dedicated to urban climate studies, e.g. The International Conference on Urban Climate (ICUC), The Inter-governmental Panel on Climate Changes, (IPCC). Indeed, the great attention that is given to the external environmental quality was in fact driven by the concept of promoting a comfortable indoor environment from outdoors, since it is found that the connection between outside and inside living spaces affect, to varying degrees, the way the occupants perceive the indoor

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environment. A number of studies that focused on evaluating the influence of external environmental conditions on the indoor microclimate has found a strong inverse correlation between the energy consumption in urban buildings and the thermal satisfaction of occupants with outdoor thermal conditions (see e.g. Thomas 2006; Rijal et al. 2007). In other words, this finding indicates that the greater the satisfaction of people with the external thermal environment the less to become dependent on active cooling systems, more to use outdoor living spaces and, consequently, less energy consumed by cooling or heating loads in indoor spaces.

The notion of comfort through a climate responsive design that ensures both the psychological and physiological well-beings of inhabitants, of which ‘thermal comfort’ is a key factor, becomes necessary in the design of the contemporary built environment. Thus, the design of outdoor spaces should be made in response to the local climate conditions in order to increase the use of outdoor spaces and provide outdoor thermal comfort while reducing energy loads in buildings. For this reason, there has been a considerable amount of research that aim to identify the sustainable built environment, and which urban forms may most affect sustainability (e.g. Jenks and Burgess 2000). The findings from such studies suggest that not one, but a number of urban forms may be sustainable (Willams 2001). Typically, the debate about the sustainable built environment, and urban form in particular, focused on increasing the density of built-up area, insuring a mix of uses, and achieving economic diversity, while meeting the social, cultural, and ethical norms of the communities involved (Kennedy 2007). With respect to that, some believe that a sustainable built environment could be achieved by applying the principles of the bioclimatic design to the design of outdoor spaces (Mills 2006). Thus, in recent years, there has been an increasing number of applied urban climate studies which take into consideration the climate dimension in designing the urban street canyon (e.g. Barring et al. 1985; Oke 1988; Pearlmutter et al. 1999; Santamouris et al. 1999; Ali-Toudert and Mayer 2006; Kruger et al. 2010). However, the quantitative technique and the relationships of the available theoretical knowledge in the real-world urban design practice are still lacking including standardisation and lack of guidelines for those wishing to use the climatological principles in urban design and planning (Oke 1984b). In addition, and in relation to the nature of the study in hand which investigates the influence of urban geometry on outdoor thermal comfort and energy use in urban dwellings at the same time, the majority of the studies that utilise the urban geometry as an urban design tool to investigate its influence on human thermal comfort in outdoor

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spaces (e.g. Gulyas et al. 2006; Johansson 2006a; Ali-Toudert and Mayer 2007; Fahmy and Sharples 2009; Lin et al. 2010; Berkovic et al. 2012), and on the energy consumption from urban buildings (e.g. Gupta 1984; Jones et al. 2007; Kruger et al. 2010; Yang et al. 2012) have tackled these issues separately and from different points of view. For instance, outdoor thermal comfort studies have focused mainly on the outward influence of urban geometries, which were mostly carried out on a single street canyon with continuous façade, while the energy use studies evaluate the inward influence of different urban geometries on the internal microclimate conditions and energy required to maintain a comfortable microclimate condition in indoor spaces. Hence, studies that investigate the influence the geometry of the contemporary urban settings, such as gridiron, on both issues at the same time are needed.