3. Conventional AC system

Before we discuss the low-cost energy-efficient AC systems, it is important to highlight the scope, significance, and thermodynamic limitations of existing AC technology, that is, vapor compression–based AC systems (VAC). Vapor compression refrigeration cycle is one of the basic and key thermodynamic cycles [43–45]. Therefore, it has been well known in the literature and, consequently, millions of refrigeration and heating, ventilation, and air-conditioning (HVAC) units are working worldwide on this conception due to its consistency and higher coefficient of performance (COP) [1]. Basic VAC cycle and its psychrometric representation for heating and cooling processes are expressed in Figure 5. It can be observed that the VAC cycle can provide cooled air (via evaporator) by cooling below dew-point of the ambient air. However, RH is controlled indirectly by means of dry-bulb temperature (DBT), which is one of the key thermodynamic limitations of VAC cycle. Similarly, it can provide sensible heating (via condenser) while providing reduced RH for the identical humidity ratio. Overall, it can be concluded that VAC cannot control the temperature and RH distinctly. In addition, it uses environmentally harmful refrigerants which are responsible for global warming and ozone layer depletion. Moreover, it consumes huge primary energy, thus indirectly responsible for environmental pollution too.
