## 4 Model Validation  
The off-design model of the SASCHCS is solved by the FORTRAN program. The solving process is exhibited in Figure 3. As shown, the introduction of a characteristic equation simplifies the iteration significantly, i.e., the calculation of the absorption subsystem depends only on the iteration, instead of the four heat exchangers (generator, condenser, evaporator, and absorber). Accordingly, the solving time reduces to approximately 20 s and the model is converged for a wide range of operational conditions. The thermodynamic properties of water and R410A are calculated by the software Refprop9[26]. The convergence is thought to be reached when the deviation is less than 0.01.  
The off-design model of the SASCHCS is verified by the experimental data of the prototype. In general, the validation consists of three sections: (1) characteristic equation of absorption; (2) model of compression subsystem based on the lumped parameter method; and (3) modeling of the hybrid system by coupling the models of both subsystems. Because the model of the compression subsystem has been verified in our study previously [23], two experiments were performed to verify the absorption subsystem and hybrid system models. The first experiment is performed to control the hot water temperature by adjusting the water flow rate of the collector to change the cooling capacity of the absorption subsystem. The second experiment is performed in the steady condition to measure the heat load. It is noteworthy that the off-design experiment of the SASCHCS cannot be performed because the inverter of the water pump in the compression subsystem has not been installed.  
The deviation between the simulation result and operational data with respect to the absorption subsystem is shown in Figure 4. The flow rate of hot water, cooling water and chilled water of the absorption subsystem during the experiment is the same as the design condition exhibited in Table 1. The inlet temperature of the hot water changes from 50 \({}^{\circ}\)C to 70 \({}^{\circ}\)C. The inlet temperature of the cooling water ranges from 30 \({}^{\circ}\)C to 32 \({}^{\circ}\)C. In addition, the temperature of the chilled water depends primarily on the cooling capacity of the absorption subsystem. The greater the cooling output, the lower the temperature of the chilled water becomes. The corresponding inlet temperature of the chilled water is approximately 16 \({}^{\circ}\)C to 30 \({}^{\circ}\)C. Each data of the experiment was measured in the steady condition. A good agreement was obtained. Most of the deviations are less than 10%.  
The validation regarding the off-design model of the hybrid system is demonstrated in Table 3. The inlet temperature of the hot water is 56 \({}^{\circ}\)C. For the compression subsystem, its inlet temperatures for the cooling water and chilled water are 28 \({}^{\circ}\)C and 12.8 \({}^{\circ}\)C, respectively. The superheating temperature is 6.8 \({}^{\circ}\)C. The flow rate of the chilled water is 1.06 kg/s. The other parameters are identical to the conditions listed in Table 1. As shown, the deviation between the simulation result and experimental data is small. The maximum relative error is lower than 4%.  
_Appl. Sci._**2018**, \(8\), 2612  
Figure 3. Solving process of model.