of energy and water efficient fixtures to achieve a more sustainable water and carbon footprint. Thus the key aims of this paper are to use high resolution, ...
Using evidenced-based data to optimise water-energy-GHG nexus efficiency programs for residential developments in Queensland, Australia 1
Edoardo Bertone1, Cara D. Beal1,3, Rodney A. Stewart2 Smart Water Research Centre, Griffith University, Qld, Australia, 2Centre for Infrastructure Engineering and Management, Griffith University, Qld, Australia 3 Corresponding Author, Smart Water Research Centre, Griffith University, Qld, Australia
Keywords: water end uses, micro-components, climate change, energy-efficient technology, carbon footprint, water and energy demand management, intervention strategies
Introduction It is becoming increasingly accepted that the simultaneous management of water and energy efficiency is essential in addressing future management climate change adaptation strategies. The conflict between water use and associated energy consumption dilemma is often referred to as the water/energy nexus. Managing such interconnected resources has significant implications on the savings (or production) of greenhouse gas emissions (GHG) (Kenway et al. 2011, Clarke et al. 2009). Thus, it follows that accurate knowledge on domestic energy and water uses can be used to predict carbon emissions and climate change impacts from the urban water cycle (Fidar et al. 2010). Nevertheless, there is a lack of measured data on simultaneous water and energy consumption from residential end uses such as shower, washing machines and taps. This is especially important in states such as Queensland, Australia where all new developments require the installation of energy and water efficient fixtures to achieve a more sustainable water and carbon footprint. Thus the key aims of this paper are to use high resolution, empirical water and energy data to explore water and energy efficient strategies that can improve the
environmental and economic sustainability of new residential developments. Methods There were two major components to the methods: (1) determining water, energy and GHG emissions from measured water end uses; (2) and calculating the optimal combination of intervention solutions (e.g. cost effective energy-efficient options) to reduce GHG emissions from water end uses. End use data acquisition The water end use data for this study was generated from the South East Queensland Residential End Use Study (n=252) (SEQREUS) using smart meters that measured flow to a resolution of 72 pulses/Litre (L) or a pulse every 0.014 L. The smart meters were connected to data loggers that wirelessly transmitted the data weekly to a central computer. This data was then disaggregated into end uses using trace flow analysis software (Trace Wizard™). Further discussion on the research methods is provided in Beal et al. (2011). The energy end use data was obtained from a small pilot study sample which metered the electricity usage of the hot water system (HWS) as well as its hot water end uses (i.e. hot water going to shower). The heating electricity and distribution of hot water
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enabled the heating energy of individual water end uses to be determined (i.e. energy of morning shower by Adult A). In addition, water use diaries that were filled out for each home in the SEQREUS also assisted in providing valuable information on water use patterns and often provided additional estimates on the proportion of hot and cold water tap usage. Finally, published values on hot water end uses and energy usage were used to confirm the data from the trial study. A water use audit had been undertaken for each home in the SEQREUS, where the model and make of every water use appliance and fixture was recorded along with the water and energy efficient star ratings. Using this information, the energy demand from each water use appliance was determined using published values in the literature or from manufacturers’ datasheets. While this approach may be potentially skewed by biased reporting of the energy usage, it was sufficient to give at least some indication of energy demand from the appliances. Calculation of GHG emissions were performed using published values produced by the Queensland electricity grid of 0.089 kilograms of carbon dioxide equivalents (kg CO2e/kWh) (Australian Government 2010). A value 0.04 kg CO2e/kWh was used for solar HWS (Perry et al. 2008).
HWS or low flow shower heads). Percentage savings from the base case scenario (worst case scenario of no efficient strategies) were calculated when comparing to a range of sequentially applied water and energy efficiency intervention strategies (e.g. solar HWS can achieve 43% reduction in energy). Results and discussion Average annual water and energy consumption breakdowns across residential end uses is shown in Figure 1. Shower, clothes washer and tap usage comprised the bulk of the water consumption (69% combined) (Fig 1a). This represents a total of 33 kilolitres per person per year (kL/p/y) for shower, tap and clothes washer (CW). Energy consumption of all the water appliances and fixtures (i.e. shower, taps, clothes and dish washers) was determined (Fig. 1b).
Optimising water and energy efficient strategies A number of scenarios were devised to determine the impact on GHG emission reductions from various water and energy efficient technologies (Table 1). The data from each scenario was based on the average consumption calculated from SEQREUS homes that met existing sets of classification conditions (e.g. a cluster of homes with solar Page 2 of 5
Fig. 1. Average annual end use breakdowns for (a) water consumption (kL/p/d) and (b) energy consumption (kWh/p/d).
Average energy consumption (kWh/p/y)
The major energy end use was shower (61%) and tap (27%). Clothes washers comprised only 4% (54 kWh/p/y) of the total energy consumption, which was less than dishwashers (DW) at 7% or 82 kWh/p/y. (Fig 1b). The energy associated with heating water is typically the major influence on household energy use (Kenway et al. 2010, Fidar et al. 2010) and this is consistent with results from this study. Hot water end uses comprised a total of 1,232 kilowatt hours per person per year (kWh/p/y).The two commonly installed HWS (i.e. electric and solar) were examined to see how different heating systems influenced the energy consumption on showers and taps (Fig. 2). Results demonstrate that solar HWS require substantially less grid energy than conventional electric systems. This is also consistent with other findings (Tsilingiridis and Martinopoulos 2010, Perry et al. 2008, Crawford et al. 2003).
A number of energy efficient intervention scenarios were modelled to quantify reductions in GHG emissions compared with ‘business as usual’ base case scenarios (worst case). The nine interventions that were explored are shown in Table 1 together with the estimated savings (%) to water and energy consumption. The results demonstrate that converting from a conventional electric HWS to a solar HWS can reduce energy consumption by at least 42% (Table 1). Results from other studies suggest that this may be a conservative estimation with reductions of up to 60% (Kenway et al. 2008), however there are many factors that influence the efficacy of solar HWS which must be considered when comparing energy reductions and subsequent GHG emissions savings. These include climate, type and location of solar cells and storage systems, and method of booster (gas or electric). Table. 1. Summary of estimated savings from various intervention strategies Intervention scenario
Clothes washer front load + cold tap only
Solar (electric boosted)
Fig. 2. Comparisons of energy demand from electric and solar hot water systems.
Conversion to solar hot water system
Percentage of total savings1
Shower reduced to average of 38 C˚ Shower reduced to average of 35 C˚ Tap aerators
Shower monitoring system
Efficient shower heads
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≥4 water star rated clothes washer
as compared to a base case home with no water or energy efficient technology
In terms of water and energy savings, the installation of a water efficient (low flow) shower head is very effective (Table 1). This technology is also cheap, relatively easy to install and usually readily available for consumers. Other studies have shown the substantial reductions to total household water and energy use from low flow shower heads (Beal et al. 2011, Willis et al. 2010, Mayer et al. 2004). Data presented in Fig. 3 further demonstrates the impact that solar HWS can have on the overall GHG generation (measured as kg CO2e/kWh) resulting from residential hot water consumption. CW Taps Total
Annual GHG emissions [kg CO2/kWh/p/y]
Energy efficient DW
Low flow shower rose
Front load, cold CW
Fig. 3. Impact of various energy efficient intervention scenarios on GHG emissions.
Using the SEQREUS database and available information, calculations show that replacing a conventional electric HWS with a solar (electric boosted) HWS, the annual GHG emissions can potentially decrease from an average of 845 to 150 kg CO2e/kWh/p/y. However, this is a slightly simplistic argument, particularly in regard to economic savings – replacing an old electric with a new solar HWS can be expensive. Calculated payback periods for solar HWS and low flow shower heads were estimated at 9.6 years and 1.1 years, respectively (data not shown). This aligns well with other reported values by where a payback period for water efficient shower devices is between 1 to 1.5 years (Willis et al, 2010) compared to installing a solar HWS which may be around 10 years (Crawford et al. 2003). Conclusions Using a data registry of high resolution water end uses from 252 households as a base, and energy data from a pilot study yielding energy data and hot water end use data from HWS, it was shown that replacing an electric HWS with a solar HWS can achieve up to 42% reduction in GHG emissions. Low flow shower heads can reduce water and energy consumption (via reducing HW demand) by 11% and 22%, respectively. Understanding the linkages between residential water and energy consumption can inform design optimisation and improve the sustainability of future urban planning. Limitations of the study relate to the energy consumption values used for generating carbon emission estimates; only a small pilot sample of HWS was instrumented (water and electricity use). Moreover, theoretical and not empirical appliance energy use data was used (although this is
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presently common practice). Ideally, all water appliance or fixture energy consumption and HWS end uses would be based on a representative sample of field collected empirical data. This is a primary aim of a forthcoming research project using 150 homes which will be monitored for energy and water end use consumption. References Australian Government (2010). National Greenhouse Accounts (NGA) Factors, prepared by the Department of Climate Change and Energy Efficiency, July 2010. Beal. C, Stewart, RA., Huang, TT., Rey, E. (2011). Applying smart metering technology to disaggregate residential water end uses in South East Queensland. Journal of the Australian Water Association, 38 (1), 80-84.
carbon footprint of locally integrated energy sectors. Energy 33(10), 1489-1497. Tsilingiridis, G. and Martinopoulos, G. (2010) Thirty years of domestic solar hot water systems use in Greece - energy and environmental benefits - future perspectives. Renewable Energy 35(2), 490-497. Willis, R.M., Stewart, R.A., Panuwatwanich, K., Jones, S., Kyriakides, A. (2010) Alarming visual display monitors affecting shower end use water and energy conservation in Australian residential households - Resources, Conservation and Recycling 54, 1117–1127 Acknowledgments The authors would like to acknowledge the Urban Water Security research Alliance for funding the SEQREUS of which much of this data was based. Disclosures The authors have nothing to disclose.
Clarke, A., Grant, N. and Thornton, J. (2009). Quantifying the energy and carbon effects of water savings, Full technical report for Environment Agency and Energy Savings Trust prepared by Elemental Solutions, April 2009, UK. Crawford, R.H., Treloar, G.J., Ilozor, B.D. and Love, P.E.D. (2003) Comparative greenhouse emissions analysis of domestic solar hot water systems. Building Research and Information 31(1), 34-47. Fidar, A., Memon, F. and Butler, D. (2010). Environmental implications of water efficient microcomponents in residential buildings. Science of the Total Environment, 408, 5828-5835. Kenway, S.J., Lant, P., Preistly, T., Daniels, P., (2011) The connection between water and energy in cities. Water Science and Technology, 63, 1983-1990. Mayer, P., DeOreo, W., Towler, E., Martien, L. and Lewis, D. (2004) Tampa Water Department Residential water conservation study. The impacts of high efficiency plumbing fixture retrofits in single family homes, Tampa Water Department and The United States Environmental Protection Agency. Perry, S., KLemes, J. and Bulatov, I. (2008) Integrating waste and renewable energy to reduce the
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