【文章內(nèi)容簡(jiǎn)介】 Unit and mullion system This is a bination of the stick system and the unit system and may be regarded as a promise of the two. It is more suitable for use in mediumsized projects so as to balance the factors of lead time, ease of installation and economy of scale. Panel system A panel curtain wall system is similar to a unit system, the difference being that a panel system has homogeneous sheet or cast panel with few joints and may not have separate mullions. Unit systems are made up of smaller ponents fabricated together to form much plex panels that capable to perform heavier duties or other more specific requirements. However, due to the relative simplicity of the system, curtain wall of panel system design may not be able to fulfill the usual requirements most highrise buildings required under Hong Kong’s environment. Its use is therefore more limited to certain kinds of buildings like those of standardized design for lowine classes or for buildings of industrial purposes. In this case, the panels can be constructed of sheet materials and manufactured in large quantity in very low cost. Columncoverandspandrel system Columncoverandspandrel system consists of column covers, which are usually made of alloyed aluminum, metal sheet or other laminated/fibrereinforced sheet, and with glazing ponents and spandrel panels that fit between them. It resembles certain similarity to a unitandmullion system except that the structure of the building is exemplified by the column covers. With the exception of the stick system and the unit system, other curtain wall systems are seldom used in Hong Kong. Structural glazing system The merit of using structural glazing system as external wall is to minimize the unglazed elements as much as possible, leaving glass panel almost as the only glazed surface on the wall. This can be done by providing larger mullion supports which span outward away frm the structural floor of a building. Special clamping devices such as a spider bracket can be used to hold the glazing panel in position. Structural sealant is used to seal up the gap between the glazing panels. DESIGN PRINCIPLES FOR EXTERNAL WALL A building enclosure may be broadly defined as a set of interconnecting elements which separate the outside from the inside. These elements would include exterior walls, a roof, other ponents such as windows and doors, and sometimes exposed floors. The function of a building enclosure is to control the peration of snow, wind, rain and sun to the inside and to contain the desired indoor climate. The enclosure must meet many individual requirments but for the purpose of this paper they are limited to the following six: control of air flow, control of heat flow, control over the entry of rain and snow, control of sunlight and other forms of radiant energy, control of water vapour diffusion, acmodation of building movements. The requirement for air tightness and consequently air leakage control is met by most curtain wall systems because the air barrier of the wall is inherent in the structural properties of glass and aluminum or steel tubes that prise the system. The continuity of the air barrier (Figure 1) is achieved by the continuity of the glass panel through the air seal at the shoulder flanges of the tubular mullion, and through the aluminum section to the other flange surface. The air seal between the lower shoulder flange of the curtain wall mullion and the metal pan of the spandrel panel provides continuity of air tightness to the air barrier metal pan and on to the next mullion connection. Such assemblies are regularly tested using air pressure to determine the structural properties of the glass, metal, and seals and to determine the equivalent leakage area (ELA) that remains. In addition, the Architectural Aluminium Manufacturers Association imposes upon its members many other requirements including a specification that the system must not leak more Thermal Insulation (Control of heat flow) The control of heat flow is generally achieved through the use of insulation. Although it is not apparent from the exterior, the curtain wall system uses considerable insulation usually behind spandrel glass or any opaque panels. Because of the materials used in the structure, ., glass and metal, which are highly conductive, the system must also contend with potential condensation on the interior surfaces. To curtail this effect, most curtain wall systems incorporate two distinct features: first, a sealed double glazed window or an insulated metal pan and second, a thermally broken mullion, usually with a PVC plastic insert and more recently, a foamedinplace polyurethane connection. A sealed double glazed window unit can acmodate an indoor humidity up to about 35% at an outdoor temperature of 25 176。 C with little condensation appearing on the glass. Similarly, the thermal break in the aluminum or steel mullion ensures that the surface temperature of the structural mullion will remain well above the dew point temperature of the air for most building types, except for high humidity indoor environments such as in swimming pools or puter centers. The thermal break also ensures that the structural mullion is thermally stable, th