Residential water heaters in Brisbane, Australia: Thinking beyond technology selection to enhance energy efficiency and level of service

• Controlled electricity tariff enhanced the performance of water heating systems.
• Night off-peak electricity tariff reduced the performance of water heating systems.
• Solar water heaters are likely to be more resilient to Legionella sp. growth.
• Water efficient washing machines may promote energy inefficiency.

A holistic approach to residential water heating systems specification is required to provide optimal energy efficiency. The objective of this study is to analyse the performance of residential water heating systems for the city of Brisbane in Australia, for different combinations of heating system technologies (solar, heat pump, electric), storage tank sizes (125 l, 250 l, 325 l), time-distribution of energy in accordance to the tariff selection (all-day, controlled, night off-peak) and washing machine water heating sources (internal and external). Performance assessments considered the influence of 54 different water heating system configurations on the electricity grid (i.e. power peaks, time-distribution of energy according to electricity tariffs, and energy intensity), as well as their level of service (i.e. compliance rates with recommended hot water temperatures). Empirical water end use data from 27 households was utilised to model the performance of water heating systems. The study demonstrated that beyond merely specifying the type of technology (e.g. solar hot water), other key criteria such as hot water demand, hot water tank size and electricity tariff selection should also be considered in order to systematically optimise the energy and service performance of hot water systems in residential buildings.