title: Residential Hot Water Services in Australia: Thinking Beyond Technology Selection to Enhance Energy Efficiency and Level of Service
Creators: name: Silva Vieira, Abel
Publisher: name: Griffith University
Year: 2019
Subjects: subject: Hot water services
subject: Energy efficiency
subject: Solar Water Heaters (SWHs)
subject: Air Source Heat Pump Water Heaters (ASHPWHs)
subject: Legionella

description: By assessing the water lifecycle from an energy perspective, it becomes clear that domestic water heating systems play a considerable role in the urban water-energy nexus. However, the paucity of studies enhancing current understanding about how significant this contribution is may prove to be an impediment for the development of feasible initiatives when developing sustainable plans for water and energy resources concomitantly. The attainment of a clear understanding of the performance of Solar Water Heaters (SWHs) and Air Source Heat Pump Water Heaters (ASHPWHs) under different operational conditions is essential for decision-making, which requires accurate estimations of electricity savings potential and associated level of service. Therefore, reliable tools to predict the performance of renewable energy and energy efficient water heaters are required in order to prevent the installation of either oversized or undersized systems in residential buildings, which may lead to unintended outcomes for carbon policies. This issue is particularly relevant in Australia, where energy efficiency policies for the residential sector must take into account a vast number of climatic conditions due to the continental size of the country. This doctoral research study addresses the aforementioned knowledge gap. The overarching study aim was to investigate the performance of renewable energy and energy efficient water heating initiatives considering technical aspects (i.e. influence of technical specifications, site-specific conditions and user behaviour) and strategic considerations (i.e. key principles for decision-making). This aim was achieved by addressing the following four core study objectives: (1) to analyse the performance of residential water heating systems for different electricity supply tariffs, hot water tank sizes, and end-uses considering energy performance and service level indicators; (2) to identify key performance parameters for ASHPWHs in residential buildings by using a multi-parametric sensitivity analysis through theoretical models calibrated with empirical measurements; (3) to identify key performance parameters for SWHs in residential buildings by using a multi-parametric sensitivity analysis through theoretical models calibrated with empirical measurements; and (4) to develop an overarching Renewable Energy and Energy Efficiency Investment Decision Analysis (REEEIDA) framework based on a comprehensive literature review, and the application of the REEEIDA framework for water heating systems. A novel set of methodology underpinned by three measurement instruments was developed as part of the PhD research project. The first instrument (i.e. data generation) encompassed empirical analyses (laboratory experiment) and theoretical analyses (computational models). The second instrument (i.e. scenarios) was used to determine representative domestic hot water service patterns taking into consideration different site-specific conditions (e.g. weather conditions, electricity tariffs, cold water temperature, hot water temperature set-point for end-uses, etc.) and water heater types and configurations (e.g. ASHPWHs and SWHs). The third instrument (i.e. indicators) was used to evaluate water heaters considering aspects related to the water-energy nexus (i.e. energy intensity, and peak-hour and total power demand from electricity grids) and the level of service (i.e. compliance levels with minimum temperature thresholds for Legionella spp. control in hot water tanks and temperature requirements at end-use points). Three predominant analytical methods were used in the study, namely: multi-criteria analysis to achieve Objective 1; sensitivity analysis to achieve Objectives 2 and 3; and REEEIDA framework to achieve Objective 4. The methods and findings related to the four objectives are provided in four aligned journal papers included as chapters in this thesis (i.e. Chapters 4 to 7). Objective 1 findings revealed that SWHs appeared less prone to Legionella outbreaks, and water efficient front load washing machines are likely to cause an increase in the energy intensity of hot water supply services. For Objective 2, it was found that the coefficient of performance and the hot water storage tank capacity are the factors that most influence the energy consumption of ASHPWHs across different cities in Australia. Objective 3 findings indicate that the dust accumulation level on collectors is a key site-specific parameter for the energy performance and level of service of SWHs, outplaying several technical specification parameters (e.g. solar collector area and efficiency). The key findings of Objective 4 show that the optimisation of investments in renewable energy and energy efficiency can lead to a 48% reduction in the required funds for carbon mitigation targets. The overall PhD research project finding demonstrates the importance of comprehensive multi-parametric analyses to achieve energy efficiency and level of service requirements for residential hot water services.