| Glass |
Martin Volker, group marketing manager of AGI (formerly Africa Glass) says this issue is potentially as crucial as the initial safety glazing campaign launched by SAGGA, and needs to be addressed. A window is the thinnest part of a building's structure. In winter, even if the windows are well-sealed and draught-proof, the glass becomes cold because it is in direct contact with the cold outside air. Just as hot air rises, so cold air sinks to the floor, producing cold down draughts.These draughts circulate the cooled air throughout the room, drastically reducing comfort levels. The converse is true is summer, where air in contact with the glass heats up, rising to create hot draughts. Although glass has a relatively low coefficient of thermal conductivity, the thin layers normally used in buildings rely on the comparatively still air close to the glass surfaces to provide a measure of insulation. The draught always present on the inner surface of single glass creates such air movement so as to negate the insulation values of the air. This leads to conduction losses throughout the glazing. Due to the insulating properties of still dry air, it is logical to increase the thermal resistance of the glazing by˜trapping' a layer of dry air between two glass panes “ hence the term double glazing, or sealed insulating glass units (SIGUs). With increasing energy costs and the negative environmental impact associated with energy generation, SIGUs have become a valuable asset to any building. SIGUs are acknowledged as energy-saving devices, and can reduce heating costs substantially. If one considers that, depending on the building type, about 30% of the heat loss is through single-glazed windows, the energy savings realized by SIGUs will result in a relatively short payback period. This could be as little as three years, depending on the glass areas, orientation, building type and other factors. Optimum solar control, as well as excellent insulation values, can be achieved when a solar-control glass is incorporated into the SIGU. This will reduce the cooling-plant capacity requirement for commercial buildings, as well as allowing buildings without mechanical cooling to maintain acceptable temperatures for far longer than would be the case with single glazing. A double-glazed room is also a larger room, as all the room space is fully utilized as SIGUs eliminate the cold spots and draughts associated with single glazing. Hence draughty window areas are a thing of the past. With the desire for more natural light and the resultant greater expanses of glass in a typical wall, SIGUs become even more important. SIGUs with the same insulation value (U-value) as a brick wall are now available. This means that, depending on the orientation, one could have floor-to-ceiling double glazing, with no disadvantage over a brick wall. When warm damp air inside a room comes in contact with a cold window pane, condensation will form on this surface. Due to the insulating properties of the dehydrated air in the SIGU, the inner space is at virtually the same temperature as the room ambient, thereby largely eliminating condensation. Apart from the loss of visibility due to this condensation, it can be so severe as to cause structural damage to the building in the form of water damage.. Thus there is no better investment from a property point of view, as a building glazed with SIGUs has enhanced market value. In addition, an SIGU offers about 20% to 30% improvement in sound control over a single glazed window. By utilizing AGI sound-reducing laminated glass of varying thickness in the SIGU, the sound transmission through the glazing can be more than halved. An important point to remember when glazing for acoustic control is that all gaps and cracks in the facade should be sealed perfectly, or else the acoustic insulation is greatly reduced. INSUL-THERM® SIGUs from AGI are manufactured from two or more panes of glass separated by means of a metal spacer, to which they are bonded with a polyisobutylene (PIB) primary seal, and a silicone or polysulphide secondary seal. The air chamber formed between the glass panes is dehydrated by means of a desiccant enclosed within the metal spacer. Where additional insulation is required, AGI recommends incorporating low-emissivity glass into the unit. This˜low-e' glass is able to reflect long-wave reradiated heat due to a special thin non-reflective metallic coating pyrolitically applied to the glass surface. This virtually invisible coating allows a high visible transmission, combined with insulation values on par with a brick wall. Therefore it is ideal for freezer rooms and the like. INSUL-THERM® can be combined with any other solar-control glass to offer a wide range of performance characteristics and aesthetic appearances Contributed by a Member of the South African Glass Association, Martin Volker AGI +27 (0) 11 621 2700 tel. (board) +27 (0) 11 622 2638 fax 
|
