## 5 Conclusions  
The objective of this work was the design of the components of a solar air conditioning facility for a hotel located in Madrid. The hotel owner wanted to take advantage of an existing field of flat-plate solar collectors to carry out a demonstration project of solar cooling.  
A simple model was developed in the TRNSYS program to evaluate the energy delivered from the hot water storage tank to the absorption chiller for the production of cold water, as a function of the collector field surface, volume of the hot water storage tank and driving temperature of the absorption machine.  
This model was validated with data registered in the installation and published previously in [17], in terms of the fraction of the solar radiation used to drive the absorption machine. It reproduced the effects of the analyzed variables on the performance of the facility experimentally observed, and provided an ideal slope of the solar collectors for this application of 20\({}^{\circ}\), and optimum values of 75 \({}^{\circ}\)C for the driving temperature and 15 L/m\({}^{2}\) for the specific storage volume.  
The differences between the registered data and the data provided by the model were justified in terms of 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.  
Nowadays, the main disadvantages of the thermal solar cooling facilities are: the high initial cost of the solar cooling facility, approximately 3000 euros per kW of cooling capacity, the parasitic electrical consumption, the risk of legionella and the water consumption associated to the use of a cooling tower, and the lack of proper maintenance.  
The starting conditions of this work (existing field of flat-plate solar collectors) do not affect its conclusions. The solar collector has a high efficiency, although it is true that its slope, as has been proven, is not optimal for a solar cooling application. As for the chiller, the offer of low-capacity absorption chillers driven by hot water is limited.  
In the field of solar cooling with absorption machines driven by hot water it is important to work in the direction of reducing the initial cost of the facility, improving the maintenance and eliminating the need of the cooling tower. However, these needs are the same as 20 years ago when the authors began working in this field.  
Therefore, more fundamental research is necessary in heat and mass transfer especially in the absorber of the absorption machine to reduce its size. Previous work indicates that it is possible [20]. In the field of maintenance, the study of corrosion (electrochemical analysis) must be deepened, a phenomenon that is produced by the presence of different metals at different temperatures. Air condensation in LiBr-H\({}_{2}\)O absorption machines is another objective on which research should be focused.  
Conceptualization, P.J.M., P.M., V.M.S., L.A.B. and J.R.; methodology, P.J.M., P.M., V.M.S., L.A.B. and J.R.; software, P.J.M. and L.A.B.; validation: P.J.M., P.M.; formal analysis, V.M.S., L.A.B., and J.R.; writing--original draft preparation, P.J.M., P.M.; writing--review and editing: V.M.S., L.A.B., and J.R. All authors have read and agreed to the published version of the manuscript.  
This research was funded by (MINECO/AEI/FEDER, UE), grant number ENE2017-83729-C3-1-R.  
The authors declare no conflict of interest.