Human thermal comfort depends on many factors: occupant factors such as the age, gender, culture, activity, clothing of the individual, and environmental factors such as air temperature, humidity and air movement. A number of comfort indicators are used
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to assess the impact of a number of climatic factors and also individual comfort zones on human comfort.
The results indicate that the higher the urban density in a particular area, the less its direct solar access through the summer. High buildings are more easily shaded than extended ones for the reason that summer irradiation is most concentrated on roofs. Construction of a double roof is the most effective process of shading the main roof of a building, but is considered to be expensive.
Overshadowing can be minimized by adding sufficient spacing, making adjustments to the grouping of houses, or by a small shift in orientation. Thus, obstruction of light is influence by height and the distance from the affected elevation. It is capable of reducing the daylight distribution in a building and might cause overshadowing. It has been shown that courtyards are considered to be the most superior form of exterior space in a hot arid climate. Colonnades can also be used to enhance solar gain control in private courtyards.
Furthermore, a south-north house provides better shading potential throughout the year compared with other orientations, while, east-west roads are perfectly orientated for solar access in winter and shading in summer. Northern and southern oriented slopes are the most shaded in summer.
The inverted pyramidal shaped structure allows partial self-protection for solar radiation during a requisite period.
External shading devices are more efficient than interior ones at preventing overheating, but carry penalties of cost and lack of control. Interior devices have lower effects on reducing heat gain in the room. Compared to internal devices, mid-pane devices provide better protection from the sun’s heat, take a longer time to get dirty and do not take up space inside the building.
It has been also established that using vegetation is the greatest solar gain control device and can both shade the house in summer and allow solar gain in the winter.
In hot arid weather, the coefficient of transmittance must be approximately 1.1 Kcal/hm2Co for an external wall to contain a suitable thermal resistance.
It has been pointed out those types of solar control glasses are not often used in current residential buildings, but have good potential for the future. They decrease thermal
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gains to the room as well as retaining the view and light. Understanding of all these factors will be applied in the case study and analysis.
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3 Chapter 3 Solar gain control design and evaluation tools
3.1 Introduction
Before the advent of current mechanical means for maintaining thermal comfort, people who lived in hot arid regions were forced to find ways to cool their homes using simple natural sources of energy and the physical phenomena around them. In general, these solutions have been found to be more in harmony with the human physiological functions than current means, such as electrically powered arid region coolers and air conditioners. This situation remains true for the majority of people in the industrially developing countries, where the conventional energy sources of the industrialized world are not readily available at affordable prices. There is a clear need to further develop traditional systems based on natural resources. Before proposing or inventing new mechanical devices, traditional solutions drawn from vernacular architecture must be considered, which can then be adapted or modified and developed to meet modern requirements. (Fathy, 1986). This procedure needs to be based on recent developments in the physical and human sciences, as well as the fields of passive cooling and, principally, solar gain control.
There are several available design tools to help the architect in the solar control design of a building. They range from moderately easy paper-based evaluation procedures to advanced computer simulations. The majority of solar control design tools are based on numerical or experiential relations. However, the user does not necessarily have to recognize these complex formulae to be able to use the tool. With the help of regulation documentation or training, the designer can gain the necessary skills and information quite simply.
The procedure of selecting the most suitable tool can be a difficult one (Ward & Rofchaei, 1995).The design tool for solar control chosen by the designer should be appropriate to the task at hand. For the early design phase, design tools need to be quick and interactive in order to allow the evaluation of alternatives without a great investment of time and effort. In some cases, the important information is not quantifiable, but is qualitative or perceptual. Alternatives can be considered at the design stage and the best solution can be chosen depending on the issue to be studied, which is analysed at the stage of the design process.
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Since the 1960’s, the use of simulation tools and computer modelling in building construction has increased greatly. However, despite over 50 years of progress, architects are still sceptical as to whether these types of tools have a role in the design procedure. The fundamental question still remains; “Does the use of computer based tools actually make better building?” The real challenge is to use these tools in the early stages of design, where an additional informed analysis of possible alternatives can yield the most advantage and the maximum cost savings, both in the economic and environmental areas.