## 2 Materials and Methods
### Validation of the TRNSYS Model  
The model developed in the TRNSYS program was validated with the data from a solar cooling facility designed by the authors and built in the Miguel Hernandez University of Elche [17] (Figure 2). This facility conditions: 200 m\({}^{2}\) of laboratories and offices. It has a collector field of 38.4 m\({}^{2}\) composed of 16 flat-plate collectors oriented toward the south with a 30 degrees slope. The hot water storage tank has a volume of 1 m\({}^{3}\). Figure 3 shows a scheme of the solar cooling system. The solar collectors supply hot water to the storage tank to drive the absorption chiller. If the solar radiation is not enough, a backup vapour compression chiller covers the cooling demand. The cold water supplied to the fan coils comes either from the solar facility or the backup system, depending on the temperature of the cold water storage by actuating the three-way valves V1 and V2 [10]. Figure 3: Scheme of the solar cooling system. Figure 2: View of the solar cooling system at Miguel Hernández University of Elche. Figure 3 also shows the positions of the sensors in the system. Temperatures were registered by Pt-100 temperature sensors and water flow rates by electromagnetic flow meters. A first-class WMO pyranometer was used to measure solar irradiance incident on the collectors. Outdoor and indoor dry-bulb temperature and humidity ratio were also registered as well as water and electricity consumptions. Table 1 shows the difference between the results obtained with the TRNSYS model proposed in this work (Figure 1) and those registered in the installation and published in [17], in terms of the fraction of the solar radiation used to drive the absorption machine. To obtain the TRNSYS results of Table 1 and validate the model, the input data were those of the Elche facility, that is, the typical meteorological year, the surface (38.4 m\({}^{2}\)), the efficiency curve (a\({}_{0}\) = 0.818; a\({}_{1}\) = 3.47 (W/m\({}^{2}\)K) and a\({}_{2}\) = 0.0101 (W/m\({}^{2}\)K\({}^{2}\))) and the inclination (30\({}^{\circ}\)) of the solar collectors and the storage volume (1 m\({}^{3}\)). Once the model for the Elche facility has been validated, it is applied for the design analysis of the demonstration facility in Madrid. The differences of 0.052 (75 \({}^{\circ}\)C) and 0.072 (80 \({}^{\circ}\)C) are due to several reasons: the use of a typical meteorological year, the difference between the performance of the solar collectors with respect to the efficiency curve supplied by the manufacturer, and thermal losses in pipes. Although meaningful, the relevance of the obtained differences will be evaluated at the end of this study. To characterize the climatic conditions in summer (June-September), a typical meteorological year was obtained using METEONORM (2007) for Madrid and Elche [14]. Table 2 shows the average daily radiation received per square meter of inclined collector surface for the months that make up the summer season (June-September) in Madrid and Elche. It can be seen that the ideal slope of the solar collectors for this application is 20\({}^{\circ}\), although for ease of construction of the supports, in these cases an inclination of 30\({}^{\circ}\) is normally adopted (sin 30\({}^{\circ}\) = 0.5). This is a value that could be considered if the owner decided to build a specific collector field for the absorption machine. The present study was carried out for an inclination of 60\({}^{\circ}\), which is the current slope of the existing solar collectors in the hotel. Figure 4 shows on the psychometric chart the conditions on an hourly basis for the summer season consisting of the months of June-September corresponding to Madrid (red dots) and Elche (green triangles). The mean and standard deviation of the outdoor dry-bulb temperature were 23.4 \({}^{\circ}\)C and 5.99 \({}^{\circ}\)C for Madrid and 24.8 \({}^{\circ}\)C and 3.53 \({}^{\circ}\)C for Elche.