1. Introduction

The word air-conditioning (AC) literally means conditioning of subjected air according to required conditions of air temperature (Ta) and relative humidity (RH) [1]. The AC phenomena usually involve five modes of conditioning, that is, (i) heating, (ii) cooling, (iii) humidification, (iv) dehumidification, and (v) ventilation. More than one AC mode could be required depending upon the nature of AC application as well as ambient conditions [2]. For example,

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cooling and humidification is required in summer season of Multan (Pakistan), whereas heating and humidification is required in dry winters of Fukuoka (Japan) [3]. Certainly, there could be numerous AC applications which may require specific conditions of Ta and RH, for example, animals' AC [4], greenhouse AC [2, 5], agricultural products' storage and preservation [6, 7], and so on. The requirements of Ta and RH vary dynamically with respect to time and may even vary from species to species [4]. On the other hand, the AC term is mostly associated with humans' thermal comfort as far as conventional literature and primary objectives are concerned [8, 9]. Therefore, lots of AC technologies have been established for humans' thermal comfort and are under practice in order to obtain typical conditions of Ta and RH, particularly for summer and winter seasons [1, 10]. Out of them, most popular and highly efficient systems are based on electric-driven compressors. Although compressor-based AC systems achieve desired Ta and RH conditions efficiently, these are thermodynamically inefficient and consume huge amount of primary energy [1, 10]. Moreover, these systems are based on environmentally harmful technologies and consume hydro-fluorocarbons (HFCs)/chlorofluoro-carbons (CFCs)/hydrochlorofluoro-carbons (HCFCs). Consequently, the conventional vapor compression–based AC (VAC) systems possess certain global warming potential (GWP) and ozone layer depletion potential (ODP). Thermodynamic limitations as well as merits/demerits of typical VAC system are highlighted in Section 3.

In the twenty-first century, lots of energy-efficient and low-cost AC systems have been studied, designed, developed and are under practice for various AC applications, for example, data center [11–13], museums [14–16], hospitals [17], automobiles [18, 19], wet markets [20], marine ships [21], greenhouses [22], agricultural products storage [7], animals' thermal comfort [6], industrial processes [23], electronic cooling [24], turbine inlet air cooling [25], and so on. Most of these systems are either thermally driven or based on evaporative cooling conception. These systems are not involved in the use of any kind of refrigerants, thus enabling zero GWP and ODP. As heat is the input energy source for thermally driven AC systems, these systems can be employed for efficient utilization of low-grade waste heat, solar thermal energy, and biogas or biomass, and so on. On the other hand, evaporative cooling-based AC systems are always handy (wherever applicable), because they only require water with small energy to run the fan. However, evaporative cooling or thermally driven AC systems are highly influenced by ambient air conditions; therefore, systems optimization will be required for each and every AC application.

From the above perspective, this chapter discusses sensible and latent load of AC required for various nonhuman AC applications. Ideal temperature and humidity zones are represented and compared on psychrometric charts. Consequently, various low-cost energy-efficient AC systems are proposed and discussed for the subjected applications. In addition, thermodynamic limitation of VAC system and scope of proposed systems is also highlighted.
