Domestic hot water systems: Environmental performance from a life cycle assessment perspective

Abstract

Four types of commercially-available domestic hot water (DHW) systems (natural gas instantaneous, electric instantaneous, electric storage and heat pump) were analysed and compared from a life cycle assessment (LCA) perspective and their environmental hotspots (stages and processes) were determined. In addition, the influence of the origin of the energy consumed during their usage was analysed and their environmental performance was compared with that of new DHW systems recently developed. A cradle-to-grave analysis was adopted by employing data provided by the manufacturer and supplemented with secondary data from Ecoinvent. The ReCiPe 2016 (hierarchist perspective) method was used to perform the impact assessment. Regardless of the type of water heater, the use stage (due to high energy consumption) was clearly the main responsible for the environmental damage by DHW systems, but the stage of production of raw materials was also important. A comparative analysis of the four current water heating systems showed that the heat pump caused the least impacts (by litre of heated water provided per year), followed by gas-fired, electric storage, and electric instantaneous in that order. The environmental burdens are highly influenced by the country in which the DHW systems are installed because the origin of the energy source used varies. New water heaters developed by manufacturer demonstrated a trend to an environmental improvement compared to the current ones, although improvements with respect to materials consumed are still required.