Environmental Engineering Reference
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this merit becomes more prominent. As a result, solar air-conditioning is an effective
means to reduce the carbon footprint of buildings.
In fact, SHAC systems can be further facilitated by building integrated installa-
tions of solar-thermal collectors, incorporating technological advancements of sorption
refrigeration cycles and component integration in hybrid design. There are now absorp-
tion and adsorption chillers with a cooling capacity of below 10 kW, which can compete
with conventional AC systems in small- and medium-scale applications. For solid desic-
cant wheels, new sorbent materials, such as inorganic zeolitic adsorbent, are appearing,
which would be more effective in regeneration by low temperature heat source. More
research work is being carried out on liquid desiccant cooling with the inherent feature
of thermal storage. Although adsorption chillers do not currently perform as well as
absorption chillers, continual improvement is being made in the working pairs, the
method of desorption and the configuration of multiple chambers. This would help
in raising the COP of the adsorption refrigeration while keeping the advantage of low
driving temperature. In point of fact, the advancement of sorption refrigeration and
air-conditioning can be beneficial beyond solar air-conditioning: in combined cooling,
heating and power, heat-driven refrigeration cycles are also essential.
There are still a number of barriers to wider application of solar air-conditioning
systems, among them spatial requirement and economic consideration. It will take
time for building practitioners to feel comfortable with this new air-conditioning
technology. More demonstration projects and operational experience of solar air-
conditioning would certainly help in convincing policy makers, building developers,
engineering practitioners and market players. Were the life cycle assessments of solar
air-conditioning better known, their environmental merit would also become known
more widely. In the trend towards sustainable urbanization, solar cooling can play
an essential role in realizing zero carbon deployment in regions with hot and humid
climates. With appropriate system integration of cooling and heating, together with a
strategy of hybrid use of renewable energy sources, more and more opportunities for
solar-thermal technologies for building use should emerge in the near future.
ACKNOWLEDGEMENT
The work described in this paper was fully supported by a grant from the City
University of Hong Kong (Strategic Research Grant, Project No. 7002765).
Nomenclature
A
Absorber of absorption chiller or adsorber of adsorption chiller
AC
Air-conditioning
ACVCC
Air-cooled vapour compression chiller
C
Condenser
COP
Coefficient of performance
COP
ch
Coefficient of performance of chiller
COP
dc
Coefficient of performance of desiccant cooling
D
Desorber
DV
Displacement ventilation
DW
Desiccant wheel
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