Switchable glazing technology for eco-efficient construction - Nanotechnology in Eco-efficient Construction - page 234

11
Switchable glazing technology for
eco-effi cient construction

C. G. GRANQVIST, Uppsala University, Sweden

DOI : 10.1533/9780857098832.2.236

Abstract : Electrochromic and thermochromic materials and devices
make it possible to construct glazings whose throughput of visible light
and solar energy can be switched to different levels depending on the
application of an electrical voltage or on the temperature, respectively.
These glazings are of much interest for eco-effi cient buildings and
are able to impart energy effi ciency jointly with indoor comfort. The
present chapter outlines the basics of the two technologies focusing on
functional principles, relevant materials, device and manufacturing
technology, as well as selected results from research and development.

Key words : electrochromism, thermochromism, chromogenic material,
thin fi lm, energy savings, energy-effi cient buildings.

11.1 Introduction

Eco-effi cient nanotechnologies offer many ways to diminish the energy that
is used in buildings, as discussed in a recent book by Smith and Granqvist
(2010). This energy amounts to as much as 30-40% of the world's primary
energy (UNEP, 2007; Glicksman, 2008), and it follows that new and improved
building technologies can have a very signifi cant impact on global warming
(Metz et al. , 2007), urban heat islands (Heisler and Brazel, 2010), and energy
security. The potential energy savings are huge (McKinsey & Co, 2009) and,
very importantly, can be accomplished without sacrifi cing the comfort and
amenities that we rightly associate with good buildings (Richter et al. , 2008).
The latter aspect is highly signifi cant since we spend as much as 80-90% of
our time indoors - in buildings and vehicles - in the most industrialized
countries (Leech et al. , 2002). Furthermore, good energy performance can
give fi nancial advantages, and a recent study of market transactions in the
USA showed that eco-effi cient (also referred to as 'green') buildings can
have higher rental rates and selling prices than comparable buildings
without the eco-effi cient attributes (Eichholtz et al. , 2010, 2011).
Windows are necessary in buildings in order to provide visual indoors-
outdoors contact and daylight. However, it is frequently the case that
the glazings let in or out too much energy which must be balanced by
energy guzzling space cooling or space heating. An important step towards

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