Cost-effective and emission-cutting water heating system based on a novel bi-level expanded P-graph configuration optimization method

Domestic hot water (DHW) systems contribute significantly to the building sector’s energy consumption and carbon emissions, making innovative optimization methods crucial for enhancing DHW energy efficiency. Existing DHW system optimizations focus on design parameters and operation modes, but their applicability is limited to specific systems and configurations, overlooking more efficient alternatives. To overcome this problem, combining visualized graphic and algebraic techniques, this study introduces a novel bi-level expanded Process Graph optimization method (BEPGOM) to optimize a DHW system with diverse component-candidates. BEPGOM effectively identifies nontrivial configurations, substantially improving economic and environmental benefits, and enhances solvability with a 98% reduction in solution space. The optimal configuration, consisting of solar heating, PCM tank, and natural gas water heater, reduces the expenditures by 18% and equivalent CO₂ emission by 34% compared to the existing base case, greatly exceeding the traditional optimization method. Its adaptability, efficiency, and accessibility make BEPGOM a valuable tool in advancing energy system design and promoting carbon neutrality in the building sector.