Page 21 - ZEB Final Report 2009-2017

Electrochromic Smart Windows for Solar Radiation Control in Buildings | 21

As smart window applications, the ECWs may decrease heating, We have carried out theoretical and experimental
cooling, and electricity loads in buildings by admitting the investigations on electrochromic materials and windows
optimum level of solar energy and daylight into the buildings and have measured and made calculations of all the solar
at any given time, meeting, for example, the contrasting radiation glazing factors for several laboratory ECWs, float
demands of a cold winter versus a warm summer climate. In glass, low-emissivity glass, dark silver-coated glass, and various
order to achieve as dynamic and flexible solar radiation control single, double, and triple pane window combinations. Fig.1
as possible, the ECWs may be characterized by solar radiation and Table 2 (Jelle 2013) show ECW examples. Miscellaneous
glazing factors, i.e. ultraviolet solar transmittance (Tuv), visible experimental studies have been conducted on ECMs, including
solar transmittance (Tvis), solar transmittance (Tsol), solar investigation of properties other than the electrochromic ones,
material protection factor (SMPF), solar skin protection factor e.g. of photochromic properties for hexagonal sodium tungsten
(SSPF), external visible solar reflectance (Rvis,ext), internal visible bronze nanorods as depicted in Fig.2 (Gao and Jelle 2013).
solar reflectance (Rvis,int), solar reflectance (Rsol), solar absorbance
(Asol), emissivity (ε), solar factor (SF), and colour rendering References: T. Gao and B. P. Jelle, ”Visible-Light-Driven Photochromism
factor (CRF). Comparison of these important solar quantities of Hexagonal Sodium Tungsten Bronze Nanorods”, The Journal of
for various ECM and ECW combinations and configurations Physical Chemistry C, 117, 13753-13761, 2013.
B. P. Jelle, ”Solar Radiation Glazing Factors for Window Panes, Glass
enables selection of those which are most appropriate for Structures and Electrochromic Windows in Buildings - Measurement and
specific smart window and building applications. Calculation”, Solar Energy Materials and Solar Cells, 116, 291-323, 2013.

FIGURE 1. Schematic drawing
of an ECW coniguration
based on the ECMs polyaniline
(PANI), prussian blue (PB), and
tungsten oxide (WO3) (left), with
corresponding transmittance
versus wavelength spectra
in the whole solar region at
different applied potentials
with highest colouration level at
+1400 mV (right) (Jelle 2013).

FIGURE 2. Photochromic
response, i.e. colour change
induced by solar radiation,
of the as-prepared Na-WO3
nanorods in (a) bleached and
(b) coloured state with optical
photos of the corresponding
samples (left). SEM image
of the as-prepared Na-WO3
nanorods (right) (Gao and
Jelle 2013).

TABLE 1.
Calculated solar radiation
glazing factor values (top)
and regulations (bottom)
for two different ECWs
as single pane windows.
The regulation level is
calculated by subtracting
the solar radiation glazing
factors for the same
ECW at the high and low
potentials (Jelle 2013).