Environmental life cycle assessment and techno-economic analysis of domestic hot water systems in China

Abstract

In this study, a cradle-to-grave life cycle assessment was conducted on several typical domestic hot water systems across five climatic regions of China. Variations of the climate and energy supply in these regions and the energy efficiency grade of domestic hot water systems were also taken into consideration. The results suggest that evacuated tube solar systems are highly energy-efficient and low-cost, except in the region with the weakest solar radiation. Electric systems are extremely energy-intensive and uneconomical for domestic hot water use, although they have the least human and ecological toxicity potentials. Solar and air-source energy systems save energy; however, they use more materials and cause more human and ecological toxicity. From the severe cold region to the hot summer and warm winter region, the heat load of domestic hot water increases by 59%, resulting in an increase of 58–230% in primary energy demand. Accordingly, the environmental impacts of domestic hot water systems increase in varying degrees; however, few impacts decrease due to the different emission factors of different power grids. The raw materials used in the manufacture of domestic hot water systems and the energy required for the use of the systems are the most important contributors to all environmental impacts. The scenario analysis indicates that 24.5% of the primary energy demand and 25.7% of greenhouse gas emissions owing to domestic hot water use in China can be reduced by improving the energy efficiency, prompting the use of renewable energy sources, and reducing the usage of materials for domestic hot water systems, as the human and ecological toxicity potentials will increase by 0.1% and 10%, respectively, due to the increasing use of certain materials.