REFLECTOR 2 WINDOWS WINDOWS
Switchable broadband infrared reflecting/transmitting windows which can reflect a large amount of infrared solar energy in summer and transmit it in winter appear to be very attractive 27, 28, 29. Furthermore, some of them interfere with visible light, requiring the use of artificial lighting to compensate. However, these reflectors only can reflect a limited fraction of incident solar light, which reduces their impact. Simple narrowband cholesteric IR reflectors (with reflection bandwidths of 100–200 nm) have also been fabricated to help reduce the thermal transmission through a window 25, 26. A limitation to these technologies is that they either cannot alter their properties with changing environmental conditions (leading to an increase in energy demand) or they absorb/scatter light in the visible region, reducing the visual contact between occupants and the outside environment (resulting in extra energy for artificial lighting to maintain the interior illumination level 21) or both.Īutonomous organic based temperature responsive infrared (IR) reflectors which reflect infrared light at elevated temperature and transmit it at lower temperature 22, 23 and a manually controlled electrically switchable infrared/visible reflector based on an inorganic material (tin doped indium oxide nanocrystals in niobium oxide glass) have been reported 24. These include shutters 8, blinds 9, electro- and photo-chromic windows 10, 11, 12, 13, 14, 15, 16, light responsive systems 17, liquid crystal based windows 18, 19 and thin inorganic coatings 20.
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A number of recent innovations have opened up new opportunities for building envelopes as a flexible compromise between these competing design objectives. In particular, windows are important design elements, as they balance access to solar gains and thermal transmission with the need for a view to the outside and consequent energy consumption for heating, cooling and artificial lighting 6, 7. This energy-intensive form of space conditioning, however, not only leads to high utility bills but also causes carbon dioxide emissions and other negative side-effects for the environment 4.īuilding envelope technologies play a major role in making the built environment more sustainable 5. In many cases, extensive use of heating, ventilation and air-conditioning (HVAC) equipment is needed to ensure that requirements for desired indoor conditions are met.
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A number of studies report an increasingly strong relation between the indoor environmental quality of buildings and the health, productivity and well-being of building occupants 1, 2, 3.