Improving the off-design modeling of a commercial absorption chiller

Abstract

Modeling a commercial absorption chiller accurately is essential for better integrating and optimizing their operation, especially in off-design conditions. Hence, in this work, a novel model based on the principles of mass and energy conservation was developed, incorporating three improvements for a single-effect LiBr–H2O absorption chiller, corresponding to (i) heat loss to the environment, (ii) heat transfer coefficient dependence on flow rate, and (iii) a falling film evaporator model. As a study case, the improved model was applied to simulate the off-design behavior of the Yazaki WFC-SC10 absorption chiller, using available manufacturer data. The effect of hot and chilled water temperature and hot water flow rate on performance were analyzed. Improvement (i) corrects the design point cooling capacity and heat input predictions to 0.03% and 0.04% error, respectively, far lower than the basic model (3.7% and 8.8%), while adding (ii) proves enough to enhance the off-design performance computation to excellent precision within 40%–100% of the rated hot water flow rate. Lastly, improvement (iii) allows the model to exhibit the performance-degrading partial wetting and overflow operating regimes at the evaporator, maintaining more realistic model predictions in off-design operation. The total model error in capacity and heat input with respect to manufacturer data (MAPE) decreased by 68% and 54% respectively, with respect to the hot water temperature, and by 94% and 82% with respect to its associated flow rate. Overall, this work sets a benchmark in commercial absorption chiller modeling accuracy, and particularly to the atypical behavior of the WFC-SC10.