# Simulation of a Solar-Assisted Air-Conditioning System Applied to a Remote School
## 2 System Description  
The thermosolar absorption air-conditioning system installed in the primary school of the community of Puertecitos, Baja California, Mexico (30\({}^{\circ}\)21'19.7\({}^{\prime\prime}\) north (N), 114\({}^{\circ}\)38'26.3\({}^{\prime\prime}\) west (W)) is composed of a field of solar thermal collectors, containing evacuated tubes with a parabolic reflector in the lower part with a total aperture area of 110 m\({}^{2}\); these solar heating technologies are responsible for maintaining optimal temperature conditions using a water storage tank of 12 m\({}^{3}\) capacity, necessary for proper operation of the cooling system. Both the collector field and the thermal energy storage tank (TEST) compose the hot water circuit. An LiBr-H\({}_{2}\)O absorption cooling system of 35 kW capacity is thermally driven by the hot circuit fluid. Due to the absorption process, heat is removed from the water that is used as a cooling medium in the chilled water circuit. For abrupt temperature changes not to affect the operation of the chiller, a 1-m\({}^{3}\) buffer tank is used in the chilled water circuit. The chilled water passes through four cooling coils with a capacity of 8.75 kW each, one in each classroom of the school, removing the thermal load when required. The heat supplied to the chiller, both by the hot and chilled water circuit, is discharged through the cooling water circuit and released into the environment with an evaporative cooling tower. Given the problems of water availability in the region and, being a community next to the sea, the cooling water circuit has two variants: normal water mode and seawater mode. In the first mode of operation, freshwater is used as a direct cooling medium for the chiller; it is fed into the absorption machine to remove the heat and transfer it to the environment with the cooling tower. When seawater is used, the cooling of the system is carried out indirectly. The cooling water circuit is divided into two; the tower is responsible for cooling the seawater and recirculates it in an independent circuit, while, in the other circuit, freshwater is used to remove heat from the chiller and, by means of a titanium coil submerged in the seawater reservoir of the cooling tower, the removed heat is transferred. This is done in order to not introduce the incrusting and corrosive compounds that the seawater carries with it into the internal heat exchangers of the absorption machine, as well as to not depend on replenishment of freshwater due to evaporation by cooling the system. There is also a diesel auxiliary heater in the hot water circuit so that, if the temperature conditions in the TEST are not met, the system can be operated. The previous equipment installed in the Puertecitos school is shown in Figures 1 and 2. The schematic diagram of the components and connections is shown in Figure 3. The solar collector field is responsible for maintaining the temperature of the TEST in the range of 75-96 \({}^{\circ}\)C, enough for proper chiller operation. Regardless of whether the cooling machine is operating or not (for example, on weekends, the chiller does not operate because there are no classes), the solar field pump continues to provide fluid for heating until the tank is completely at the set point temperature, in this case 96 \({}^{\circ}\)C, always seeking to have the system in operating conditions. When there is a need for classroom air conditioning, the chiller turns on and the TEST pump supplies hot water from the top. Since the temperature of the generator of the absorption machine is at an optimal level for operation, the pump of the chilled water circuit is turned on to bring it to the cooling coils of the classrooms, at a temperature between 7 and 10 \({}^{\circ}\)C, removing the heat from the spaces to be air-conditioned. This current is taken to the chiller to be cooled again. It is worth mentioning that the configuration of the  
Figure 1: Evacuated tube solar collector field with a bottom parabolic reflector.