Solar-desiccant air-conditioning systems - Solar Energy Sciences and Engineering Applications - page 508

The provision of optimum human living conditions results in large amounts
of energy consumption. The energy required to maintain human thermal comfort
approaches 50% of total building energy consumption. In most cases, the energy
needed is high-grade electric power (IEA, 2008). As most power plants consume large
amounts of fossil fuel in generating power, so provision for optimal human living stan-
dards has contributed to high carbon-based energy consumption and greenhouse gas
emissions (IEA, 2004). Alternative methods are therefore needed when talking about
reducing conventional energy consumption and cutting greenhouse gases emissions
(Coiante and Barra, 1996). However, it is imperative not to sacrifice healthy indoor
and thermal comfort conditions for the sake of energy consumption reduction (Costa
and Costa, 2006; Day et al., 2009).
16.1.2 The building environment
At present, maintaining clean indoor thermal comfort conditions is done using
refrigerant-based air-conditioning systems (AC). The operation of refrigerant-based or
vapour compression systems is by means of altering the pressure of the working fluid
to change the boiling point and thus release or absorb latent heat. However, the opera-
tion of changing the pressure can only be done by mechanical means, for which pumps
or compressors are used; thus, the so-called mechanical vapour compression system
(ASHRAE, 1989). In addition, at present, most of the working substances are made
from halocarbon compounds such as CFC and HCFC which affect the ozone layer
through emissions of greenhouse gas (GHG) (Calm and Didion, 1998). These materi-
als have a long-term effect on the general environment. Hence, the systems maintaining
indoor thermal comfort conditions are gradually harming the natural environmental,
causing ozone-layer depletion and greenhouse gases emissions.
The provision of indoor thermal comfort conditions for buildings, either through
heating or cooling, is done by heat pump systems. These devices are widely called
mechanical vapour compression systems. Several studies have been conducted to
improve system performance through efficiency and reduce environmental damage.
However, these systems still consume large amounts of energy in the form of high-
grade electricity. The main energy source of mechanical vapour compression systems
comes from electricity power grids. These air-conditioning systems play a major role
in the energy consumption of buildings, most particularly in hot and humid climates.
In the Middle East, more than 70% of building energy consumption is to support
cooling (El-Dessouky et al., 2004). In Europe, 10% of building sector energy con-
sumption is likewise to support cooling demand (Kolokotroni and Aronis, 1999). In
Hong Kong, 45% of commercial building energy consumption is also for cooling (Zain
et al., 2007). In Japan, 3% of building sector energy consumption is for cooling appli-
cations (Murakami et al., 2009). It is expected that in tropical countries which are hot
and humid, energy demand for cooling and dehumidification will be very high (Wong
and Li, 2007).
Commercial, office and industrial buildings commonly use centralized air-
conditioning systems with heat pumps or refrigerant chillers. However, split-type
air-conditioning systems provide an alternative. The application of centralized air-
conditioning systems will introduce fresh air inside the buildings. However, it will also
increase energy consumption as treatment of outdoor air latent and sensible energy