Exciting new developments in building envelope technology are changing the aesthetic and functional characteristics of building envelopes. These emerging technologies sometimes offer radical changes to the building envelope in terms of energy use, thermal behaviour, performance, and aesthetics, potentially changing the ways in which buildings are operated.
Electrochromic glass
Electrochromic glass, incorporating a thin film that changes its opacity when an electrical voltage is applied, can quickly transition from a clear to dark appearance. Typically without the need for any electric voltage to maintain an opacity level, glazing returns to its transparent state when voltage is applied again. Darkening (and lightening) occurs from the edges, moving inward, and can take several minutes.
Providing dynamic shading control for the building envelope, electrochromic glass can obtain visual transmittance ranges from around 60% for the clear state, down 4% for tinted state. The solar transmittance (SHGC) also changes, from 0.48 in the clear state to 0.09 in the tinted state.
Self-cleaning glass
Self-cleaning glass typically uses a thin film of titanium dioxide on the #1 or exterior surface as a photocatalytic coating. Photocatalysts are compounds that use the UV bands of sunlight to facilitate a chemical reaction. When exposed to sunlight, the titanium oxide triggers a strong oxidation process that converts noxious organic and inorganic substances into harmless compounds.
The self-cleaning process on glass involves two stages. In the photocatalytic stage, organic dirt breaks down when the glass is exposed to sunlight. Next, in the hydrophilic stage, rain washes the dirt from the glass by picking up the loose particles. This is an effective way of keeping the glass clean without high maintenance costs. However, in drought-prone locations with low precipitation, the second stage may require some intervention and maintenance.
Photovoltaic (PV) glass
Photovoltaic (PV) glass integrates crystalline solar cells or amorphous thin films that generate energy from light and are integrated into laminated or double-glazed units. There are two general types of PV glass: semitransparent and opaque.
Semitransparent PV glass is similar to patterned ceramic frit, allowing some light to penetrate through the glass while giving occupants views to the outside. Opaque PV glass uses solid PVs and is appropriate for spandrels and other non-vision areas of the building envelope.
Double-skin façades
Double-skin façades consist of distinct exterior and interior glazed wall systems, separated by a ventilated air cavity. The cavity creates a thermal buffer between the interior and exterior environments and can be ventilated by natural convection caused by warm air naturally rising, by mechanical devices, or by a hybrid mode that combines the two.
In some double-skin façade designs, the air cavity is interrupted vertically or horizontally (or both) by solid or perforated partitions. Selection of the type of the glazing, the width and partitioning of the air cavity, and the ventilation mode depends on the climate, building orientation, and design requirements.
Classified according to the ways the air cavity is partitioned, the ventilation mode, and the airflow pattern, these three variables can be combined in numerous ways for a wide variety of design double-skin façade possibilities.
Selection of the double-skin ventilation mode (natural, mechanical, or hybrid) should be based on building location (i.e., climate zone). The approach to partitioning should be based on cost, functional requirements, and the number of floors. Natural ventilation of the air cavity works best in temperate or cold climates; mechanical ventilation may be required for hot climates. Hybrid systems will often use natural ventilation during the colder winter months and mechanical ventilation during hot summer months, making this mode applicable for mixed climates.
The majority of double-skin façade to date have been used for buildings in temperate and cold climates. However, some buildings in warm, hot and arid, and hot and humid climate types are successfully using double-skin façades, incorporating natural or hybrid-mode ventilation, integrated movable shading devices, hybrid ventilation systems, and different airflow patterns.
Vacuum-insulated panels (VIPs)
Vacuum-insulated panels (VIPs) are an emerging class of insulating materials consisting of a core of insulation material (usually silica or glass fibre) enclosed in an airtight, vacuum-sealed film envelope.
VIPs have up to one-seventh the thermal conductivity of conventional insulation materials are not finished materials, so they should be used within non-glazed building envelope elements or behind curtain wall spandrels. Because VIPs have such good insulating qualities, their use can decrease the thickness of an exterior wall without harming its thermal performance.
The vacuum between the two lites of glass places them under negative pressure, pulling them toward each other. To counteract this, a grid of spacers made of a material with low conductivity and are spaced apart from each other in both directions. Vacuum-insulated glazing units are typically thin (between 6 mm and 12 mm), making them ideal where high-performance glazing has to be installed in existing frames.