الفهرس 
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Abstract
This study discusses the building envelope from the environmental design point of view. The building envelope (or the building skin) is the external layer that wraps the building. It includes everything that separates the interior and the exterior of a building. It plays a great role in demotic control which has its direct effect on maintaining human comfort, and energy conservation. An energy-efficient building envelope decreases the need for energy consumed by appliances (like HVAC and lighting systems) through decreasing heat gains and accessing homogenous natural day tight and natural ventilation in addition to other functions. In addition to fulfilling these functions the envelope systems are integrated in the architectural design to serve for the building aesthetics.
The study discusses the title in three parts after a brief introduction that shows the environmental goals that the building envelope should help to achieve. Part I discusses ”The Basics of Building Envelopes”, Part II discusses the ”Building Envelope Systems”, and Part III discusses ”Intelligent Building Envelopes”.
PART I: ”The Basics of Building Envelopes”
L;”his part discusses the basics that help understand the enve&ope systems that are discussed in Parts II and III.
The building envelope performs several functions, some are general and others are environmental functions. The envelope performs various general functions as it serves in the building aesthetics, controls physical access to the building and providing visual communications between the interior and the exterior. It also provides security, durability, and controls noise transmission. It can be act as a digital screen for multimedia uses.
The envelope performs environmental functions through climatic control (thermal control, natural ventilation and natural lighting), and energy conservation and production. Both environmental and general functions of the envelope are discussed in Chapter I ”Functions of Building £envelopes”.
To control thermal transfer and natural ventilation through the envelope, it should first be clear how the natural’ phenomenon of heat transfer occurs. Heat transfers in three modes: conduction, convection and radiation. They usually act together in a combined mode. Each mode should be treated to control heat transfer. This is discussed in Chapter II ”Principles of Heat Transfer”.
PART II: ”Building Envelope Systems”
This part discusses the different $)’Stems of the building envelope and its main elements, which serve for energy-felinely and environmental control.
There are two main strategies needed to maintain human comfort. And which consume a large amount of energy when treated by active systems. These are heating and cooling, which are usually achieved using HVAC systems. Building envelope systems can help reduce heating and cooling loads on HVAC systems or totally eliminate them, without consuming energy. This can be acceptably achieved by the envelope through passive heating systems and passive cooling systems.
Passive heating systems include three systems: direct gain system, indirect gain systems (which include Thrombi walls, convicted loops, Barras system, and thermal collector roofs and walls), and isolated gain system (sunspaces). These systems are discussed in Chapter I ”Passive heating Systems•.
Passive cooling, on the other hand, includes three main strategies: excluding heat gains, inducing air movement, and cooing the inlet air. Excluding heat gains is the first step in passive cooling, which depends mainly on shading systems and other systems (like double roofs and walls, thermal mass, insulation, surface coloring and advanced glazing) that aim to reduce solar heat gains. Cooling inlet air is achieved through evaporative, geothermal and radioactive cooling systems.
Insulation methods are effective in decreasing heat gains. These can be formed using fabricated insulation, or by using natural) materials that have high isolative properties, like straw in straw bales, which is very effective and have many important environmental benefits. Cooling systems are discussed in Chapter” ”Passive Cooling Systems•.
Shading Systems greatly help in excluding heat gains. They can be divided into external and internal systems. Each type includes many systems that effectively reduce heat gains. Shading systems, and their installation places and techniques are discussed in Chapter III ~~Shading Systems”.
Glazing is usually a weak point in the envelope’s thermal performance. However, energy-efficient glazing systems provide different solutions to reduce heat gains while admitting a suitable amount of daylight to the interior. These systems have spectrally selective properties (that admit visible light radiation while prevent heat radiation) or angular selective properties (which allow the glazing to admit sunlight of certain altitude angles and reflect or redirect those of other angles. These systems are discussed in Chapter IV: ”Energy-Efficient Glazing Systems•.
Energy production is a function that can be effectively applied in the building envelope. It is applied through installing photovoltaic panels on suitable places on the envelope. Photovoltaic can be placed on the buildings roof (mounted PV system) or can be integrated with the fa9lde design in the form of an architectural element. These systems are discussed in Chapter V: ”Bui’ding-’nteerated PV systems”.
PART III: ” Intelligent Building Envelopes tt:
As climatic climatic conditions are neither static nor fixed, then it WI” be hardly a possible mission for a building envelope to achieve maximum efficiency unless it is capable of changing its properties or positions of its elements in response to external conditions. A dynamic envelope (or an active fa9-de) can respond to these conditions.
The idea of intelligence in the building skin learns from the human skin how responsive it is to the climatic conditions. To perform responsive actions the intelligent building envelope is supplied with sensors to ’sense’ the external conditions. The responsive changes that the building envelope performs are controlled by a building management system (BMS) that plays the role of the brain in the human body. It takes the decisions that are suitable to adapt the envelope in response to external conditions. The concept of intelligence of the building envelope is discussed in Chapter I ”The Concept of Intelligence-.
Most commonly, intelligent envelopes are double skin facades (or active facades) as movable systems are installed in the cavity which provides a safe place for these mechanisms and decreases their need for maintenance. This type of facades is discussed in Chapter” ”DoubIe-£nveIope facades».
The study discussed the capability of applying the previous systems in the building envelopes in Egypt, and showed examples of buildings that include energy-efficient features in their envelopes, and that are built or design in Egypt. This is discussed in Chapter III ”Application of Energy-Efficient Building Envelopes in E~ .