## 1 Introduction  
Conventional vapor-compression cooling systems require large amounts of electrical energy to operate: This promotes energy consumption based on fossil fuels [1]. In recent years, research and technology development have been focused on efficient energy use as well as renewable energy sources to mitigate environmental problems (such as global warming or air, water, and soil pollution) and other related energy issues [2]. Among renewable energies, geothermal energy is considered to be an abundant and constant source of thermal energy, unlike thermal solar energy [3]. Geothermal resources of a high temperature are generally being utilized for electricity production, and the installed capacity is continuously growing [4]. However, despite the vast potential of low-to-medium temperature geothermal resources, they are not being used because there are technical limitations to electricity generation (by low-temperature heat), low energy conversion efficiency, and high investment and production costs [5; 6]. However, there is considerable potential for geothermal energy at a low-to-medium temperature (<150 \({}^{\circ}\)C): According to [PERSON] [7], there is a potential for 1410 EJ/year. Air conditioning absorption systems are some of the most interesting devices, since they use low-to-medium temperature heat sources [8]. Air conditioning absorption systems operate with environmentally clean working fluids and require lower electricity consumption than conventional systems, so CO\({}_{2}\) emissions are very low [9]. Absorption systems can be used for large-scale applications, their cost is lower with respect to other thermally driven systems, they consume a negligible amount of electrical energy, and they have few mechanical parts [10]: This is an environmentally friendly method in order to produce air conditioning. However, a combination of renewable thermal energy and an absorption chiller mainly depends on the coupling temperature [11]. A single-effect absorption cooling system consists of a generator (G), an absorber (A), a condenser (C), an evaporator (E), and a heat exchanger (SHE), as can be seen in Figure 1. Heat is supplied to the generator to separate part of the refrigerant from the working mixture. The refrigerant goes to the condenser and then to the evaporator through the expansion valve. The refrigerant is evaporated, producing a cooling effect, and then goes to the absorber, where it is absorbed by the solution coming from the generator. The diluted solution is pumped to the generator, starting the cycle again. Compared to the single-effect cycle, the half-effect cycle has two solution circuits, one of them at high pressure and the other one at low pressure, as can be seen in Figure 2[12]. The heat is supplied to both generators (G\({}_{HP}\) and G\({}_{LP}\)) at the same temperature. The refrigerant fluid produced by the first solution circuit (in G\({}_{LP}\)) is absorbed in the second solution circuit (in A\({}_{HP}\)). Meanwhile, the refrigerant fluid vapor produced in the high-pressure generator (G\({}_{HP}\)) is condensed, expanded, and evaporated to produce a cooling effect. The refrigerant fluid leaving the evaporator goes to the low-pressure absorber (A\({}_{LP}\)), where it is absorbed by the solution coming from G\({}_{LP}\). The new strong solution is pumped to G\({}_{L}\), starting the cycle again. The half-effect cycle, despite having relatively low values of the coefficient of performance (COP) compared to the simple effect cycle [12; 13], has the peculiarity that it can operate at extreme operating conditions, such as high condensing temperatures and low generation temperatures. Figure 1: Pressure–Temperature diagram for a single-effect absorption cooling system. In the literature, there have been many reports about theoretical and experimental works on single- and double-effect absorption systems: However, the literature about absorption half-effect systems is scarce.