Solar-desiccant air-conditioning systems - Solar Energy Sciences and Engineering Applications - page 510

Figure 16.1.2 Singapore pattern of the residential air-conditioning operation (Chua and Chou, 2010).
residential buildings commonly operate air-conditioning systems at night, during the
hours of sleep. As most residential buildings operate air-conditioning systems at this
time, in terms of electric energy consumption, this is the off-peak period. However,
in terms of indoor air quality, problems arise due to the recirculation of indoor air,
resulting in a poor quality indoor environment.
16.2 THE BASIC CONCEPT
16.2.1 Thermodynamic processes
Thermally operated air-conditioning systems run by means of applying heat energy
for the production of cooling effect (Grossman, 2002). However, as technologies
are varied in operation principles and heat requirements, some thermally operated
air-conditioning technologies have limited applications (Henning, 2007; Fan et al.,
2007). The main advantage of these systems is the direct application of thermal energy
for system operation. Hence, low-grade thermal energy can be used to operate the
system. In addition, several thermal energy sources can be utilized for the system
operation, such as waste heat (Henning et al., 2007). The concept of a thermally
operated air-conditioning system is the utilization of a higher thermal energy source
to drive the air-conditioning system and provide cooling effect. Figure 16.2.1 shows
the general thermodynamic principle of the thermally operated cooling system for air-
conditioning applications. The concept is based on four temperatures - the Carnot heat
engine (Abrahamsson and Jernqvist, 1993; Hellman, 2002). However, the system still
utilizes electric energy for the operation of fans, pumps and the control system. Com-
bined thermal energy and electric energy can be generated from solar energy through a