Although glass may seem like an essential component for buildings, i.e. letting daylight and solar radiation in and keeping wind and rain out, conventional glass performs horribly when it comes to controlling heat gain and loss and keeping bodies comfortable against temperature extremes.
Double (or triple) glazing and smart Low-E and heat absorptive and/or reflective glass may have it all covered, however, that is not always the case. Glass alone cannot cover all contingencies and the hotter it is in the summertime, the less successful it is. Highly insulated glass units with Low-E coatings work well in the winter; problem is, in summer, un-shaded glass lets a lot of heat in, which very efficiently overheat buildings and people. To overcome this, heat absorbing and reflective glasses were developed and are used in all-glass facades in climates where the sun’s heat becomes a major problem.
The body is highly sensitive to small changes in radiant temperatures; that’s why we love radiators, heated floors and mass surfaces in buildings to retain heat and keep us both warm and cool. But if glasses are tinted, it progressively absorbs more and more heat itself and it becomes in effect a large plate radiator. So the darker the tint, the more heat it absorbs and then eventually re-radiates even when it’s double-glazed, such as in IGUs. Most software tools do not assess this at all because they are focused on building air temperature and HVAC design – not the comfort of its building occupants.
Fixed or operable external shading solves all of these issues and allows less deeply tinted glasses to be used. Although this may create nuisance glare in offices, in multi-unit residences, shaded windows and covered outdoor entertainment areas open up a multitude of design possibilities that can create much higher levels of energy efficiency and more comfortable thermal conditions. In conclusion, all-glass buildings will have no part in the future’s sustainable city.
On October 21 2015, Nanjing University (NJU) of the People’s Republic of China and Syracuse University in New York, USA, signed...