Energy, exergy, economic and environmental analyses and optimization of a novel vapor injection autocascade heat pump for high-temperature water heating

•A novel high-temperature vapor injection autocascade heat pump is proposed.•Energy, exergy, economic and environmental analyses are conducted by simulation.•The novel system improves the heating efficiency by 51.8% over the baseline system.•Single-objective optimization can improve the heating efficiency by 12.4%∼14.0%.•Multi-objective optimization is conducted to obtain the optimal solution.