BW Communities

Keeping Up The Right Façade

BW Online Bureau Nov 08, 2014

<?xml version="1.0" encoding="UTF-8"?><root available-locales="en_US," default-locale="en_US"><static-content language-id="en_US"><![CDATA[Modern airport designs often incorporate extremely large areas of glass facades; probably partly due to the overall trend in construction industry driving ever more glass on building façades, and in part due to the architect's desire to afford passengers unobstructed views on the surroundings, as well as on planes landing and taking off. One of the first considerations that typically comes to mind when designing the glazed façade of an airport is that spaces tend to be very large and are thus difficult to heat up in winter and cool down in summer. The façades should be designed in such a way as to minimise heat flow, thus reducing the heating or cooling needs. This can be done in a variety of ways, depending on climatic conditions. In areas where there are large seasonal variations, with cold winters and hot summers, thermal conduction through the façade represents an important factor to be controlled. This is measured by a performance parameter called U-value which represents how much heat enters (or exits) the building by unit of façade, based on the temperature difference between the inside and the outside of the building. There are several ways of controlling the U-value of the building. The first step is to reduce the wind-to-wall ratio. Spandrel panels are typically insulated and thus offer very low U-values. This particular technique may not be compatible with the architectural design, though. The second technique consists of adopting double-glazed units (DGUs) for vision areas. DGUs have a much lower U-value than monolithic glazing (less than half, typically). When this is not sufficient, a third technique involves filling DGUs with a rare gas such as argon, which further lowers the U-value for even greater efficiency. Another aspect of heat losses through the façade is related to radiant heat (infra-reds). To minimise this type of heat loss, glazed panels can receive a layer of ceramic frit (a type of permanent paint) that helps reduce heat flow through the façade. The colour and density of the frit needs to be selected judiciously so as to not hamper outward view through the glass. One alternative that can be used in combination or independently from the one above is to use low-emissivity glass. This type of coated glass helps reduce infra-red transmission, while allowing natural visible light to enter the building. Low-emissivity coatings incidentally also help reduce the U-value discussed above, which represents a double benefit of this approach. Glass colour also plays an important role in this respect. Green and blue glass generally perform best (more light than heat flows through), while grey glass is the worst overall (more heat comes in than visible light). As a last resort, or if mandated by aesthetics, external shading devices can also be used on the façades. While it is important to control heat and visible light, reflectivity can make or break the façade of an airport. If the façade material is too reflective (glossy metal cladding, reflective glass, etc.), it may affect pilots landing and taking off, as well as controllers in the control tower. This represents a potential danger, thus needs attention. It may not be very easy to control with complex, articulated façades, since reflectivity varies with the angle at which the surface is viewed. One other important consideration when designing the façade of an airport is acoustic control. Planes can generate very high noise levels. Sound transmission through the façade should be controlled to reduce this noise to acceptable levels within the airport. Fortunately, airports are typically fairly noisy places, given the high density of people and the level of activity inside, thus the noise criteria is not extremely stringent. Typically, laminated glass or DGUs are sufficient to achieve acceptable noise levels internally. If higher levels of noise cut-off are required, then it is possible to consider laminated DGUs, which offer outstanding noise-reduction performance. The actual solution varies from airport to airport, depending on local regulations, as well as the expected size of aircrafts that will be using the airport. <table style="width: 600px;" align="center" border="2" cellpadding="8" cellspacing="8"> <tbody> <tr> <td><img src="/businessworld/system/files/airports_580x178.jpg" style="vertical-align: middle;" width="580" height="178"></td> </tr> <tr> <td>(From left) Kolkata Airport and Delhi Airport</td> </tr> </tbody> </table> This last point also ties in with "wind loads" on the façade. Reactors of large aircrafts can generate tremendous draft, which can affect the façade of the terminal. Airports are often designed with "blast barriers" to divert these air jets away from the façade, but in cases where the façade will be subjected to heavy gusts from aircraft engines, designers should ensure that glass or cladding panels are secured and won't be blown away. While on the topic of blasts, airports are valuable infrastructure assets for a country, and as such are often the target of terrorists. In cases where local security forces envisage a potential threat, airports façades need to be design with blast mitigation measures. This can range from simply extending the stand-off distance, thus reducing potential damage, to hardening measures preventing a blast from having a large impact on the structure and its users. Designing and building the façade of an airport presents some key challenges. This brief overview provides a glimpse into some of the technical issues that designers are faced with, as well as some solutions that can be implemented to address those issues. However, the actual implementation of these measures requires a large amount of knowledge and experience in the particular requirements of airports. The author is Managing Director of Meinhardt Facade Technology(S) Pte Ltd