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Architecture Department 4-1 Introduction In warm sunny climates, architects should control the amount of sun radiations reaching the building before designing it. The excess solar gain may results in increasing the internal solar gain and cooling loads which leads to increasing the company running costs. Presence of solar control glass and shading devices on the glazing facades could prevent excessive solar gain. They can also improve user visual comfort by controlling glare and reducing contrast ratios which often leads to increase satisfaction and productivity. Solar control and shading can be provided by natural landscaping or by building elements such as awnings, overhangs, and trellises. Some shading devices can also function as reflectors like light shelves, which bounce natural light for day lighting deep into building interiors without entering direct sun radiations. Shading devices could be: fixed or adjustable, vertical or horizontal and could be external or internal. Moreover, interior space could be protected from direct sun radiations by using solar control glazing materials in the building facades. This chapter will introduce the types of innovative solar control shading devices and glazing materials, as well as it will study their performance on blocking direct solar radiation from entering the space. 4-2 Architecture Considerations of Efficient Shading Designing an efficient shading system varies with variation of many factors like: building location, orientation, site, and building usage. It is difficult to generalize the architecture considerations of efficient shading device as there are wide ranges of building types and climates. But the following considerations can come true: • Exterior shading is most effective than interior shading in reducing the cooling loads, since the solar radiations have already enters the space incase of interior shading. However, the interior devices control the glare and permits visual comfort. • The designer should carefully consider the durability on selecting the shading devices, with considering its maintenance costs. • Shading devices affects natural light, but some solar control devices can make use of both natural light and shading like: the insulated glazing and solar control coated glazing. • If shading attachments are not aesthetically acceptable, the architect can use the building form itself for exterior shading. So that to set the 137 window back in a deeper wall section or to extend elements of the skin to visually blend with envelope structural features. The architect should consider the climatic conditions and comparative shading coefficients of shading devices before selecting the appropriate shading device1 for a given building. These two considerations will be explained in the following section. 4-2-1 Climatic Conditions The building requirements for solar protection or solar gain are determined in the first stage by the site climatic conditions. In very cold or very warm climates, shading decisions are really quite easy as the building design should have solar penetration or not. But in moderate climates, there will be times when solar radiation is of significant benefit as a heat source and times when it could be a problematic due to glare and overheating. The first key design issue in this case is to determine the time when temperatures go from being cold (that require heating) to warm (that require solar protection) and vice versa. Following some considerations for selecting an efficient shading device depending on the climatic conditions: • Limit as much as possible the amount of east and west glazing. • Consider shading on the roof even if there are no skylights since the roof is a major source of transmitted solar gain into the building. • The architect should study the sun angles before selecting the efficient shading device. • The design requirements for a shading device depend entirely on a building's use with the climate condition. For example, for a multi- storey open-plan office building in a relatively warm climate, the occupancy and equipment gains so much heat energy; this may means that heating is rarely required. In this situation, to avoid unnecessary loads, exterior shading devices should be selected to completely block sun radiations all year-round. While, in climates where summers are also relatively cold, the requirement may even be to allow full solar access all year-round. 1 Donald Prowler and Associates, Sun Control and Shading Devices. PDF, Revised and expanded by Joseph Bourg, Millennium Energy LLC, WBDG 2008. 138 4-2-2 Shading Coefficients The Shading coefficients (SC) is the fraction of solar radiation that transmitted by the specified device, compared to the amount of solar radiation incident upon it. They are expressed as a decimal value without units between 0 and 12. The lower the SC the less solar heat passes through, thus the more effective solar control device. The table below compares the Shading Coefficients (SC) of various shading devices. Shading Device SC 33mm clear float glass 1.0 Standard Double Glazing 0.9 Internal Venetian Blinds (fully drawn) 0.5- 0.9 Internal Curtains (fully drawn) 0.4- 0.8 Internal Roller Blinds 0.4-0.8 Heat absorbing glass 0.7 Vegetation and trees 0.6 Solar Control glass 0.4 External Blinds (fully drawn) 0.2 External Shutters (fully drawn) 0.2 Table 4- Shading Coefficients (SC) of various shading devices 3 From the previous table, the maximum solar radiation is passed through clear float glass façade, this means that clear glass facades without shading device is considered inefficient for buildings located in sunny climates. While minimum solar radiations are transmitted through presence of external blinds, so it considered an efficient shading device that can be presented on building’s glazed facades located in sunny climates. 4-3 Effectiveness of Different Shading Devices on Building’s Facade Proper shading greatly reduces the cooling loads for building having large areas of unprotected glazing. Choosing an effective shading device depend on the solar orientation of the building façade, For example, simple fixed overhangs are very effective on shading the south-facing windows in summer when sun angles are high. However, the same horizontal overhangs are ineffective at 2 Shading: Solar Control, Ecotect WIKI, accessed 2009, http://squ1.org/wiki/Solar_Control 3 Ibid. 139 blocking low afternoon sun from entering west-facing windows during heat gain periods in the summer4. While adjustable shadings are more flexible, they can be adjusted easily according to the sun direction to prevent the sun radiation from entering the space. The following section will study the performance of fixed and adjustable shading devices. 4-3-1 Fixed Shading Devices Fixed shading devices are usually integral part of the building’s structure; it depends mainly on the incident angle of the sun’s rays. There are two types of fixed shading devices: Horizontal overhangs and vertical fins. Each one has its distinctive shade pattern on the building façades. Horizontal overhangs are most effective for southern windows. In summer they can block the sun radiation; in winter they can admit lower position radiations from the sun. However, fixed horizontal overhangs may cause some problems during the spring, as October is still considered a warm month but sun has law radiations, so it penetrates and causes overheating to the interior5. Fixed shades can not ensure complete adjustment of shading with changing the shade needs all over the day. But its advantage is that it needs no handling by the occupants as well as no maintenance is needed. 4-3-2 Adjustable Shading Devices Adjustable shading devices have much better effectiveness than fixed ones. They can change their position manually or automatically with the changing pattern of the sun motion as well as, it can adapt to changing climatic conditions and shading needs. Adjustable shading devices allow the user to choose the desired level of shading. This could be particularly useful in spring and autumn when heating and cooling needs are variable. It is particularly useful for eastern and western elevations, as the low angle of the sun makes it difficult to get sufficient protection from fixed shading. It gives greater control while enabling daylight levels and views to be manipulated. Appropriate adjustable systems include sliding screens, louver screens, shutters, retractable awnings and adjustable external blinds. 4 Sun control and shading devices, accessed 2008, http://www.wbdg.org/resources/suncontrol.php 5 Baruch Givoni, Climate Considerations in Building and Urban Design, publisher John Wiley and Sons", 1998 P62. 140 4-4 Shading Techniques Shading techniques could be externally or internally to the building facades whatever it is fixed or adjustable system. The choice of appropriate shading device from the wide range of external and internal systems depends on the latitude, orientation, building type an overall design of the building. External shading devices are more effective than interior ones as they obstruct the sun radiations before it reaches the interior of the building. Modern architecture is mainly subjected by glass and transparency; glazed facades create a visual connection between outside and inside. When talking about commercial places, it needs daylight, comfort environment, but it is strongly influenced by the sunshine. So, the solution is protecting the building from direct sun radiations with the permeation of natural daylight to enter. Figure 4- External controllable louvers
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