## 3 Results and Discussion
### Two-Stage Chiller Performance Model Simulation
#### 3.3.1 Effect of Operating Conditions  
In the adsorption chiller, the operating, heat source and cooling temperatures have a major influence on the cooling capacity and COP. Effect of Heating Source Temperature  
As the driving force, the hot water inlet temperature is one of the key parameters for the adsorption chiller. Figure 9 shows the cooling capacity and COP for the two-stage chiller with heat recovery cycle, if the heating source temperature was varied. Furthermore, chiller water outlet temperature versus heating source temperature is shown in Figure 10.  
Figure 6: Effect of heat recovery time on chiller average cooling capacity and COP. It is shown that a lower chilled water temperature could be produced by increasing the heating source temperature. This is because methanol vapor is desorbed faster at a higher desorption temperature. Figure 8: Temporal history of bed, evaporator and condenser temperatures with heat recovery. Figure 7: Temporal history of bed, evaporator and condenser temperatures without heat recovery. The average cooling capacity increases from 1 kW to 7 kW when the heating source temperature increases from 50 \({}^{\circ}\)C to 100 \({}^{\circ}\)C due to the higher methanol concentration level. The COP increases with increasing the heating source temperature. The cooling capacity increased sharply and the outlet temperature of chilled water decreased with increasing heating source temperature since the methanol is desorbed faster at a higher desorption temperature, causing more methanol to be adsorbed during the next adsorption process. Figure 10: Effect of heating source temperature on chiller outlet temperature. Figure 9: Effect of heating source temperature on chiller average cooling capacity and COP with heat. Effect of Chilled Water Inlet Temperature  
In this part, the influence of changing the evaporating temperature was investigated by varying the inlet temperature of the chilled water. Figure 11 shows the effect of inlet, chiller temperature on chiller average cooling capacity and COP with heat recovery. The COP increases with increasing evaporating temperature since, in that case, the higher concentration variation of methanol can be achieved, which increases the heat required for adsorption and desorption and so prolongs cycle time. The influence of changing cooling water temperature was investigated by changing the inlet temperature of the cooling water. The cooling water temperature is a very critical actor for both adsorption and condensation processes. Figure 12 shows the effect of inlet cooling water temperature on chiller average cooling capacity and COP with heat recovery. It is very obvious that cooling capacity and COP increased by lowering the cooling water temperature. This is because more methanol vapor is adsorbed at lower temperature for a given cycle time. Figure 11: Effect of inlet chiller temperature on chiller average cooling capacity and COP with heat recovery. Comparison with Carnot Cycle COP  
The COP of the Carnot cycle was used to evaluate model results since it provides the maximum COP that could be achieved at given operating conditions. The chiller allowed for running at optimum parameters for mass flow rates, switching time, cycle time, heat recovery time, optimum heat transfer coefficients for beds and evaporator heat exchangers, in addition to optimized activated carbon mass. The results of the model were compared with Carnot cycle COPs at different chiller nominal operating conditions except hot water inlet temperature. The chiller without heat recovery mode achieved a very low COP when compared with the Carnot cycle COP, while the heat recovery mode results were very close to the Carnot cycle COP, as shown in Table 3.  
Figure 12: Effect of inlet cooling water temperature on chiller average cooling and COP capacity with heat recovery.