Anatomy of a sub-tropical Positive Energy Home (PEH)
Highlights
► Integrated systems approach addresses triple bottom line of sustainability. ► Thermal comfort maximised through providing user options for seasonal variations. ► Energy efficiency and renewable provide household resilience. ► Energy supply strategy for technology optimisation provides energy security and resilience.
Introduction
Energy consumption and greenhouse gas emissions attributable to the built environment globally are significant and growing (Levine et al., 2007). Accounting for roughly half of the building sector’s energy impacts, Australia’s 8.4 million dwellings (2006 census) are responsible for 10% of the nation’s total energy consumption and 13% of greenhouse gas emissions. Total energy demand and greenhouse gas emissions from housing are rising due to growth in the building stock and to lifestyle choices (ASBEC, 2009). Queensland (QLD) is Australia’s most energy intensive state, heavily reliant on fossil fuels, and the residential sector (1.66 million dwellings) accounts for 4.5% of the State’s total energy use, or 7.7% of total electricity consumption (Environment and Resources Committee, 2010). Residential dwellings in Australia, predominantly detached houses, have not historically been constructed with energy efficiency or thermal comfort in mind. For example, despite the relatively benign climate of south-east Queensland, the region has more than 1.6 million refrigerative air-conditioners servicing 1.2 million dwellings (Queensland Government, 2011). The strong growth in reliance on air-conditioning is a major contributor to increases in household energy consumption and greenhouse gas emissions. Average annual energy use per household in Qld is estimated at 7210 kW h (19.75 kW h/hh/day) and greenhouse emissions at 7292 kg CO2e, accounting for 20% of the national residential emissions (Atkinson, 2010).
The buildings sector has the best potential for dramatic emissions reductions, with an iterative integrated design process offering greater benefits than the incremental energy efficiency improvements resulting from an individual device/design solution approach. Estimates of 30–50% reductions in greenhouse emissions, using currently available technologies, have been made (UNEP Sustainable Buildings & Construction Initiative, 2009). In comparison with programs aimed at low energy buildings or green buildings, the zero energy or zero carbon building approach is thought to have the greatest potential for energy and carbon reduction in the building sector (European Council for an Energy Efficient Economy, 2009). In the United States, the Zero Energy Home (ZEH) concept is expected to “begin to diffuse into the market as early as 2012” and “has the potential to reverse the upward trend in new home energy consumption and begins to decrease the energy consumption of the entire US housing stock even as the cumulative number of homes continues to rise” (NAHB Research Centre, 2010). Australia’s National Building Energy Standard-Setting Assessment and Rating Framework currently being formulated for the period 2011–2020, will continue to set increasingly stringent minimum performance standards over time and will incorporate the building envelope, the energy efficiency of key building services and a consideration of how building performance can be maintained through commissioning, operation and maintenance. This may or may not include adopting a ‘zero energy’ target (Senior Officials Group on Energy Efficiency, 2010).
The common definitions of zero energy buildings essentially reflect accounting variations in what is being measured (energy, electricity, carbon emissions or dollars), what energy services and forms are included in the demand (e.g. all electric and gas services) and types and boundaries of the energy supply (e.g. primary or end use energy). All definitions assume significant energy efficiency as a first step (Torcellini and Crawley, 2006, Marszal et al., 2011, Carlisle et al., 2008). Common terminology includes
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Net zero energy home: energy consumption vs energy generation (onsite/source).
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Net energy solar home: onsite generation is solar.
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Net zero energy costs ($ earned from exports vs $ spent on imports).
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Net zero energy emissions/zero carbon home.
The purpose of this paper is to report on initial analysis of a triple bottom line (TBL) sustainability strategy utilised for this zero emissions sub-tropical house and its performance outcomes in its first full year of occupancy. Immediate household and environmental benefits will be quantified, followed by a discussion of key learnings and implications for various industry sectors.
Section snippets
Method
This paper represents part of a broader research program that utilises quantitative and qualitative approaches to better understand both the process of designing and constructing a sustainable house, and the actual performance of such houses, from the perspectives of the end client (the household). This specific case study adopts a qualitative and quantitative approach to identify and analyse the strategies utilised by one family to achieve an energy positive, zero emissions house, and the
Thermal comfort
The house ‘as constructed’ was simulated to achieve 50% better energy efficiency (9 stars – 14.3 MJ/m2/year) than ‘as designed’ (7.5 stars – 31.6 MJ/m2/year), reflecting some construction improvements made during construction (e.g. additional insulation), a refinement in details entered into the modelling software, and improvements made in the modelling capacity of national simulation software. The 9 star rating represents the actual building energy rating, not the adjusted rating allowed under
Discussion
The specific energy goals for the house could be ascribed to the Triple Bottom Line (TBL) of sustainability: economic (energy and water self-sufficiency; resilience; adaptability), environmental (passive solar design; low embodied energy) and social (thermal comfort; universal design). How has the integrated systems approach to the provision of household energy services, driven by the end user in collaboration with the architect, delivered on the triple bottom line?
Conclusion
Measured performance data for this house has shown that it achieves high levels of thermal comfort, a significantly reduced energy demand and an energy supply strategy that enables the home to be net zero emissions for all stationary energy use. The benefits for the household extend beyond environmental considerations of greenhouse gas emissions. The enhanced comfort levels (e.g. 96% of time between 18 and 28 °C; 1% of time >30 °C and 2% of time <18 °C) means that this family does not rely on
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