Performance analysis and optimization of a solar assisted heat pump-driven vacuum membrane distillation system for liquid desiccant regeneration

Abstract

Liquid desiccant air-conditioning (LDAC) system is one of the excellent alternatives to conventional vapor compression refrigeration system due to its great energy-saving potential. However, regeneration of diluted liquid desiccant is the main energy-consuming process, and its performance plays a significant role in LDAC system. Recently vacuum membrane distillation (VMD) is becoming an emerging and promising separation process rely on the advantage of high permeate flux and low energy losses. The interest of usage solar energy techniques for feed solution heating in VMD systems is regarded as a sustainable path for membrane distillation process. In this work, a solar-driven VMD system incorporating a vapor-compression heat pump for liquid desiccant regeneration is introduced. An adapted solar/heat pump hybrid heating strategy has been devised to establish a connection between the heat-demanding process and the solar thermal supply. A comprehensive multicriteria assessment of energy, exergy, and environmental evaluation is conducted, and the influences of crucial parameters on both key components and system performance are evaluated to ensure a systematic examination. Results show that both the COP and STEC decrease obviously with the growth of the inlet solution temperature, whereas SEEC is improved abviously from 410.6 kW·h/m3 to 566.1 kW·h/m3 due to the effect of heat pump. The exergy analysis indicates that exergy losses in solar collector and stratified heat storage tank accounted for over 80 % of the total exergy losses. Additionally, single-objective optimization and multi-objective optimization are employed to explore the optimum operating conditions of key componets and whole system. Results show the ideal optimal solution can be obtained with a COP of 19.92 and a SEEC of 142.89 kW·h/m3 when the weights of COP and SEEC are taken as [0.5, 0.5].