Civil Engineering Reference
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100
Semiconducting
Metallic
80
60
40
20
0
0.05
0.1
0.15
Thickness (
0.2
0.25
0.3
μ
m)
100
Semiconducting
Metallic
80
60
40
20
0
0.05
0.1
0.15
Thickness (
0.2
0.25
0.3
μ
m)
11.7 Computed data on luminous (upper panel) and solar (lower
panel) transmittance as a function of the thickness of VO 2 fi lms in
semiconducting ( τ < τ c ) and metallic ( τ > τ c ) states. From Li et al.
(2010).
￿ ￿ ￿ ￿ ￿ ￿
The fi ndings in Fig. 11.7 permit an identifi cation of two properties of
thermochromic VO 2 fi lms that severely limit their applicability to energy-
effi cient fenestration:
the modulation of solar energy, given by
Δ
T sol
T sol (
τ
<
τ
c ) - T sol (
τ
>
τ
c ),
is no larger than
10%, and
T lum is no higher than
40% for fi lms with a signifi cant magnitude of
Δ
T sol , which is too low for most applications to windows in real buildings
(Wigginton 1996).
A third limitation, obviously, is that the change of the solar transmittance
should take place in the vicinity of a comfort temperature of
25°C, whereas
τ
c
68°C for bulk VO 2 (Morin, 1959).
 
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