Electrochromic glazing in building

 Introduction

Electrochromism is the phenomenon where the colour or opacity of material changes when a voltage is applied. This is used to make electrochromic smart windows for skylights, facades, and curtain walls that can block ultraviolet, visible, or (near) infrared light instantaneously and on-demand.

Electrochromic glass, which can be directly controlled by building occupants through integrated building automation, mobile and voice control, is popular for its ability to improve occupant comfort, maximize access to daylight and outdoor views, reduce energy costs and provide architects with more design freedom.

Working principle

An electrochromic material is made of transition metal oxides like tungsten trioxide (WO3). A 3-D nanoporous structure with "tunnels" is formed which allows dissociated ions ( H+, Li+) to pass through the substance when an electric field is applied.
WO3 + n(H+ + e-) → HnWO3

A smart glass consists of 7 layers of which first and last are transparent glass of silica (SiO2). Applying a high voltage (4 V or more) will push lithium-ions into the electrochromic layer, deactivating the material. The window is fully transparent now. By applying a lower voltage (2.5 V for example) the concentration of Li-ions in the electrochromic layer decreases, thus activating (N)IR-active tungsten oxide. This causes the reflection of infrared light.

Necessities

● Light influences our body and mind. Light-sensitive cells regulate biological functions such as sleep, mood, alertness.
● There is a negative impact of poorly daylit and view-less spaces on mood, job satisfaction, health, and productivity of employees.
● Interior manually controlled shades are ineffective in preventing overheating issues. Since they usually remain lowered, the room does not benefit from daylight harvesting, resulting in higher heating and electrical lighting.

● Architects are constrained from conventional building envelopes when balancing architectural design with comfort and energy efficiency.

Advantages

● During the summer season, electrochromic glass reduces the need for heating by providing passive solar gains when clear.
● In the winter season, it minimizes the cooling loads when tinted.
● It also allows optimum use of the daylighting all year long.
● It can have a significant impact on reducing the energy bill by saving up to 34 percent in cooling loads and 29 percent in electrical lighting use.
● It provides the occupants with 98% UV protection and 40% solar reduction.
Applications

● Hospital: It has been proven that natural lights help patients recover faster. Daylight also increases the performance of the medical staff. Mercy Orthopaedic Hospital and Fair View Ridges Hospital in the USA are true examples.

● Offices: It improves the productivity of the workers. Also, the indoor temperature always remains pleasant, despite the numerous sources of heat from the computers. The UBISOFT company in France has implemented this feature.

● Educational Institutions: From Colorado State University to Chabot College, studies show that students learn material 20%-26% faster in a classroom with natural light and views of the outdoors. It makes a lecture hall more comfortable, and a library more conducive to cognitive thinking.


WRITTEN BY:Priyasha Das and Shivangi Baral


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