A comprehensive 4E assessment of a solar-powered direct contact membrane distillation system for sustainable greywater management in residential buildings

The escalating global water crisis, combined with rising energy demands in residential buildings, poses significant challenges for sustainable urban development, particularly in arid regions. Traditional water management strategies frequently neglect greywater recycling, and conventional treatment methods are both energy-intensive and environmentally damaging. This study presents an innovative solar-powered greywater purification system integrated into a residential building in Tehran, Iran, which combines direct contact membrane distillation (DCMD) technology with solar thermal collectors to simultaneously address water scarcity and enhance energy efficiency. A comprehensive 4E analysis was conducted using multiple simulation tools: DesignBuilder for building energy demand assessment, TRNSYS for solar collector and storage tank modeling, and MATLAB code for DCMD system simulation. The results demonstrate that the system, operating with a feed temperature of 60 °C, achieves a permeate flux of 80.65 kg/m2.h, meeting 53.3 % of residents' domestic hot water demand. The DCMD system exhibits an exergy efficiency of 44.36 %, with the potential for enhancement through reducing the heat transfer across the membrane. Economic analysis reveals promising results, with the solar collectors providing heat at a levelized cost of $0.017/kWh and the DCMD system purifying water at $2.38/m3. The environmental impact assessment shows significant carbon dioxide reduction, preventing 70,185.58 kgCO2 emissions annually. The system achieves a remarkably short payback period of three years when considering both carbon tax savings and avoided natural gas costs. This research presents a viable solution for sustainable water management in arid regions like Tehran, where immediate actions must be taken to mitigate water scarcity.