Numerical study of GAX ammonia-water absorption chiller using plate heat exchangers
A generator/absorber heat exchange (GAX) absorption cooler using waste heat or solar energy with the ammonia-water (NH3-H2O) working pair to produce cooling down to -20 °C is a potential solution to reduce electricity consumption and greenhouse gas emissions. Previous parametric studies of the GAX cycle were mostly conducted under the assumption of constant heat exchanger effectiveness. In this study, a new model was developed based on effectiveness values determined for different operating conditions to improve the accuracy of the simulation. The results showed a significant reduction in deviation between simulation results and experimental data when the thermal and mass effectiveness parameters were optimally adjusted. Specifically, the average relative deviation of the cooling capacity and the coefficient of performance (COP) decreased from 16 % to 1.6% and from 8% to 2%, respectively. Furthermore, the developed model was applied to evaluate the impact of the two-phase state of the refrigerant at the inlet of the condenser, which can reduce the machine performance by up to 10%.