Dynamic modelling and control of single, double and triple effect absorption refrigeration cycles

Abstract

The present study aims to design and investigate the performance of a multivariable PI controller for the control of single, double and triple effect absorption refrigeration (ABR) processes. Dynamic modeling of ABR has been previously reported in literature for single effect systems using LiBr/H2O and NH3/H2O and for double effect systems using LiBr/H2O, whereas there is a lack of such models for triple effect systems. With few exceptions, existing implementations employ reduced-order models, mainly focused on heat exchangers, whereas the rectification process is generally omitted. For the first time, comprehensive dynamic models that include the rectifier and a multivariable control scheme are presented for a) a double effect, and b) a triple effect ABR using NH3/H2O. The main control challenge is to efficiently meet cooling loads while maintaining the performance level expressed as sustainable energy usage. The control strategy consists of multiple temperature, flowrate, level and capacity control loops, in order for the system to withstand the effect of anticipated disturbances (ambient conditions variation and part load operation). The presented case study confirms the controller ability to achieve the desired dynamic behavior both in the case of performance optimization and part load operation.