Modeling and Simulation of a Two-Stage Air-Cooled Adsorption Chiller with Heat Recovery Part II: Parametric Study

Abstract

This study is the second part of the theoretical study of “Modeling and Simulation of a Two-Stage Air-Cooled Adsorption Chiller with Heat Recovery”, which is based on developing a theoretical model for a two-stage adsorption chiller with an activated carbon/methanol pair. The following models were conducted numerically using MATLAB. The model was based on 10th order differential equations; six of them were used to predict bed, evaporator and condenser temperatures, while the other four equations were used to calculate adsorption isotherm and adsorption kinetics. In this second part, bed heat exchangers and evaporator and condenser heat exchangers are studied by varying the parametric design of a chiller. This includes but is not limited to activated carbon mass inside a single bed, overall heat transfer coefficient for the bed and evaporator and the mass flow rates of all components comprising the chiller. The optimum values increased the COP from 0.35 to 0.4, while the cooling capacity was slightly changed. The COP is 95% of a Carnot cycle working at hot water temperatures as low as 60 °C, and 90% at hot water temperatures as high as 90 °C. It was found that the simulation model results for the two-stage air-cooled chiller agreed well with the experimental data in terms of cooling capacity (6.7 kW for the model against 6.14 kW for the experimental result at 30 °C cooling water temperature). The model optimized the adsorption/desorption time, switching time and heat recovery time to maximize both cooling capacity and COP. Moreover, the model is used to study the effect of activated carbon mass, size of beds and mass flow rates of cooling, heating, chiller and condenser on both cooling capacity and COP.