INSIGHTCORE ® -
School of Architecture, University of Illinois at Urbana-
Buildings are responsible for around 40% of world energy use and residential buildings as an important sector consumes a significant part of this energy. The main part of the energy used in residential buildings is consumed for space heating, cooling and lighting. Solar energy as an important constituent of climate could be utilized passively for heating and cooling living spaces and providing daylight. Designing residential blocks could affect the amount of solar radiation received by inside and outside the buildings. It is assumed that orientation, residential block form and landscaping are the main design factors which determine the optimum use of solar energy and hence the need for space heating or cooling of buildings by conventional energy sources. This paper aims to study the impacts of orientation, form and landscaping on solar access in order to find the optimal residential block configuration that benefits solar conditions and provides as much solar irradiation in colder seasons and shade in warmer seasons. In this regard, the current literature and evidence are reviewed. The results of these studies indicate that proper passive solar design should consider orientation, form and landscaping as key buildings’ parameters in order to provide enough solar access in different seasons.
Keywords: passive solar design, orientation, residential block form, landscaping
Buildings are responsible for at least 40% of energy consumption in most countries and also one third of global greenhouse gas emissions (UNEP, 2009). It has been predicted that the energy consumption of buildings will continue to increase in the future as a consequence of the growth in population, increasing demand for building services and comfort levels and the rise in time spent inside buildings (Perez-
Figure 1. Average household energy consumption division (EIA, 2010)
There are three main factors which could influence the amount of energy consumption in a residential building: outdoor and indoor design parameters (such as form, ratios, orientation, landscaping, and materials), systems performance parameters (such as efficiencies of lighting, boiler and other equipment) and residents’ behavior. Among these factors design factors are extremely effective which could determine the potential for renewable energy supply and the use of low carbon technologies (Cheng et al., 2011). Among different renewable energy sources, the most pollution free, limitless source of energy is solar energy, which could be utilized with active and passive solar design strategies and technologies (Hangemann, 2005). Solar energy is an important constituent of climate and is highly important for human thermal comfort. Solar radiation could be utilized passively for heating and cooling living spaces and providing daylight. Designing urban blocks and open spaces could influence potential for passive solar gains inside and outside the buildings and therefore, outdoor and indoor environment. Therefore, designing residential urban blocks in a way which creates proper solar access could enhance the energy performance of buildings.
In order to utilize solar energy passively, the main complexity faced by the designer in shaping urban blocks and open spaces is the difference in the seasonal internal and external desires. For instance, in summer protection from the sun and in winter solar access are required. This paper aims to find configurations of urban blocks with a residential function that benefits solar access and provides appropriate solar irradiation in cold seasons and shade in warm seasons. Hence, the current literature and evidence are reviewed in order to analyze the influence of urban and architectural parameters such as orientation, block forms, and landscaping.
2. Passive Solar Design: Definition and Benefits
Passive solar design can be described as the utilization of the sun's energy together with the characteristics of a local climate and selected building materials to maintain thermally comfortable conditions within buildings directly (Morrisey et al., 2011; Rabah, 2005). Therefore, passive solar design should arrange the form, fabric and systems of a building to use the energy from the sun for heating, cooling and lighting in order to reduce the consumption of conventional fuels (1). A passive solar system consists of four separate components: (1) collection, (2) storage, (3) distribution, (4) control. In a passive solar building, the solar components are parts of the building itself rather than separate subsystems (Passive Solar Handbook). Therefore, the building structures are used as a collector, storage, distribution and control mechanism, with a minimum amount of mechanical equipment. This definition fits most of the simple systems where heat is stored in the basic structure: walls, ceiling or floor.
Passive solar design represents lots of benefits [Passive Solar Handbook; Spanos et al., 2005) such as:
It has been proved that architectural and urban design parameters such buildings' orientation, form, and landscaping could provide the optimum use of solar gain and microclimatic conditions to minimize the need for space heating, cooling and lighting of buildings by conventional energy sources (Owens, 1992; Jabareen, 2006). Therefore, proper passive solar design should consider above-
3. The Role of Orientation in Passive Solar Design
Among the parameters that should be considered in the passive solar design of buildings, orientation is the most fundamental and generally, most easily addressed aspect of passive solar design (Chwieduk and Bogdanska, 2004). The orientation of a building influences the level of solar radiation which receive on the buildings' façade directly as well as shading and the performance of solar envelope Chwieduk and Bogdanska, 2004; Mingfang, 2002; Capeluto, 2003). There are a lot of benefits of optimal building orientation (Pacheco, 2012) such as:
It has been proven that the southern orientation is optimal in most climates in order to gain heat in the winter and control solar radiation in the summer (Mingfang, 2002; Capeluto, 2003; Pacheco, 2012). Therefore, the longer axis of the building should lie along east-
Furthermore, Shaviv (1981) conducted a study on the various orientation of the glazing façade of a building and concluded that the maximum energy saving could be obtained when the main glazing façade of the building faces south. The results of this study are shown in Table 1.
In addition, Aksoy and Inalli (2006) analyzed the relation between heat demand and building orientation by using three models with various shape factors (1/1, 1/2 and 2/1). They studied these models with and without heating insulation. According to this study, by combining the orientation, shape and heating insulation the maximum heating energy saving (36%) achieves when the longest walls oriented toward the south (Figure 2).
However, orienting the longest wall of the building or urban block is not always possible, particularly due to definite orientation of the site as it could be longer on the west and east sides. In such cases, designing the plan of the building could be really effective and vital. For instance, auxiliary spaces, kitchen, bathrooms and staircase should be places in the west façade as this side of the building receives the most solar radiation in the summer and afternoon. Moreover, in order to minimize solar heat gain, openings should be avoided on the west or sufficiently shaded by using verandahs (Ahsan, 2009).
Figure 2. Heating energy saving, depending on shape and orientation (Aksoy and Inalli, 2006)
4. Impacts of Residential Block Form on Solar Access
Solar energy falling on an urban area is received either by buildings facades and roofs or by the ground between buildings (Okeil, 2010). It is obvious that the configuration of the buildings (in a small scale) and urban blocks (in a medium scale) could affect the amount of solar radiation which is received by above-
There are three basic types of built forms (Okeil, 2010; Feng, 2004; Al-
There are several studies which have evaluated the impacts of built form on solar access in different climates and seasons. Robins and Macdonald (1999) analyzed the effects of street design parameters (width and orientation) on solar access to the urban canopy. They studied four street widths: 10, 15, 20 and 25 m, with two orientations; E-
In addition, Okeil (2010) tried to find an optimal residential block form in order to minimize solar gain in summer and maximize solar access in winter. In this regard, he compared the direct solar radiation distribution on urban surfaces among three generic forms: tow conventional forms (linear urban form and courtyard) and one proposed form which was called Residential Solar Block (RSB) (Figure 5). The computer program CITY SHADOWS, was used to carry out solar exposure calculations.
Urban form: Linear Urban form: Courtyard Urban form: Residential Solar Block
Figure 5. Three generic urban forms studied for incident solar radiation (Okeil, 2010)
The results of the simulation are shown in table II. According to this table, it could be concluded that the RSB received more solar radiation in winter in comparison with the linear urban form and courtyard. In summer, the RSB results in a decreased solar radiation falling on facades compared to courtyards and an increased solar gain in compared to linear urban form. In March/September the RSB solar exposure is very similar to that of the linear form and slightly higher than that of the block form (Okeil, 2010).
5. Landscaping in Passive Solar Design
Landscaping plays a significant role in creating the microclimate of a place. Appropriate landscaping could enhance the solar energy performance of the buildings. It is an efficient way to provide a protection from direct sun and reflected light carrying heat into a building from the ground or other surfaces particularly in summer (Meier, 1991). There are three main properties of vegetation which could influence the microclimate of a place directly: (1) shading, (2) evapotranspiration, and (3) windbreak (McPherson, 1994). In order to create proper landscaping, these properties of vegetation should be considered according to site comfort requirements (Ali-
Trees as a main element of landscaping contribute significantly to utilize the solar energy received the building. Trees could provide solar protection to buildings in summer and therefore, reduce the energy demand for cooling. A study by Shashua-
As a result, in order to utilize solar energy by landscaping, trees and vegetation should be placed in an appropriate orientation based on their properties. Hence, deciduous trees which provide shade in summer and sunlight in winter should be planted on the west, southwestern, and south side of the buildings. In contrast, evergreen trees should be planted on the north and north-
Solar energy is the most pollution free and limitless sources of energy which could be utilized passively for heating, cooling and providing daylight for living spaces. It has been established that architectural and urban design parameters such as orientation, configuration, and landscaping could influence the amount of outside and inside solar access and therefore energy performance of the buildings. Among above-
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