SAMPE Journal - May/June 2021 - 37
INTRODUCTION
Buildings and transportation sectors consume
around 40%1 and 23%2 of the total energy in
which temperature regulation for buildings3 and
automobiles with window systems took 60%2
and 23 to 41%4,5 of the energy consumption,
respectively, resulting in excessive greenhouse gas
emissions6-10. Due to high electricity demanding
using air conditioning systems, new approaches
for cooling have been developed in recent years.
One of these approaches is passive radiative
cooling without energy input for both indoor and
outdoor environment11-13, often achieved using
spectrum selective films12,14-26. The principle for
these films can be explained as follows. When
an object is exposed to outdoor environment,
its temperature can be influenced by thermal
radiation, conduction, and convection. The cooling
power Pcool can be calculated as:
Pcool=Prad (T)-Patm (Tabm)-PSun-P(cond+conv)
[1]
where, Prad (T) is the power radiated out by the
object; Patm (Tabm) is the absorbed power radiated
by atmospheric thermal or surroundings; PSun
is the incident solar power; Pcond+conv is the power
lost due to convection and conduction. In passive
cooling practice, the idea is to reduce PSun while
maintaining the other three terms constant,
especially Prad(T) through utilization of materials
transparent to lower energy radiation emitted by
the heated object. The question is how to reduce
PSun which could be reflected or scattered and/or
absorbed by shielding materials.
It is obvious that the high energy wavelength in
the solar spectrum, i.e. ultraviolet (UV) and visible
light (Vis) with higher energy must be reflected
or shielded for passive cooling purposes. These
materials or material systems have been developed
over the years. For example, in passive cooling of
buildings, most solar control films are made of
layered materials with a thermal emitter and a
solar reflector based on the photonic properties of
the coated materials27. In the cooling of automobile
cabins, films or coatings for smart windows are
generally made of electro-, photovoltaic4, and
thermal chromatic materials triggered by an
electric voltage or a predesignated temperature
at which nIR (800-2500 nm) is reflected to reduce
IR irradiation, in addition to shielding UV light.
These mechanisms often require additional energy
for monitoring and have complicated control
systems. Relatively less has been reported about
translucent or transparent cooling films made
of nanoparticles (NPs) and polymers. Fan et al.
w w w. s a m p e . o r g
May June 2021 Journal.indd 37
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SAMPE Journal - May/June 2021
Table of Contents for the Digital Edition of SAMPE Journal - May/June 2021
Table of Contents
SAMPE Journal - May/June 2021 - Cover1
SAMPE Journal - May/June 2021 - Cover2
SAMPE Journal - May/June 2021 - Table of Contents
SAMPE Journal - May/June 2021 - 2
SAMPE Journal - May/June 2021 - 3
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SAMPE Journal - May/June 2021 - Cover3
SAMPE Journal - May/June 2021 - Cover4
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