Net zero greenhouse gas emission residential building concepts for warm climates

Abstract

Combating climate change and reducing the environmental impacts of human activities is the most urgent and challenging science and policy issue of the current time. Over 32% of global energy use and nearly 40% of global greenhouse gas emissions (GHG) can be attributed to building construction, maintenance, and service. These emissions may potentially increase three-fold by 2060 due to the rapid population growth and increased access to adequate housing, electricity, and improved facilities for the billions of people in developing economies. The dominant share of these GHG emission-intensive activities will occur in Asia, Africa, and Latin America, all of which have humid subtropical and tropical climates. Consequently, there is an urgent need to address environmental impacts related to the rapid growth of the residential construction sector in these climates. The goal of this thesis is to advance the development of sustainable, low GHG emission design strategies and residential building concepts, particularly those aimed at emerging countries covered by humid subtropical and tropical climates at the policy and design level.

The work presented in this thesis first focuses on improving the transparency and credibility of the net-zero GHG emission building definition and principles, whose implementation in the building design and national building policy is recognised as one of the most promising strategies for decarbonisation of the construction sector globally. The key methodological factors from selected international building standards and schemes were first identified and analysed and then organised and categorised into transparent and easy-to-understand frameworks. The results of the analysis determined that regulation type, system boundaries for both operational and embodied life cycle related GHG emission, approach (static vs dynamic) to the “time” aspect and the possibilities of GHG emission compensation are the most critical issues that should be focused on before creating a country-specific (net) zero GHG emission building framework.

The second research activity investigated the influence of climate conditions, electricity grid mix, and the level of energy efficiency requirements present in the local binding building regulations in Sydney, Atlanta, Shanghai, and New Delhi (all located in humid subtropical climate) firstly on the life cycle GHG emission balance, and secondly on the consequent feasibility of achieving the net-zero GHG emission performance target with a case single-family building powered by grid-connected, on-site PV energy system. The results indicate that high-level energy-efficiency requirements present in the mandatory building standards in Sydney and Atlanta enable low energy operation and to achieve the net-zero GHG emission performance target with the analysed case building.

On the building design level, a systematic literature review was performed to identify the current state of the life cycle GHG emission profile of residential buildings in humid subtropical and tropical climates, as well as identify effective design strategies to reduce both embodied and operational GHG emissions and existing research gaps.

The results demonstrated that residential buildings with net-zero energy or low-energy performances could reduce the total life cycle GHG emission by 50–80% compared to the most common conventional energy performance of residential buildings, characterised by low energy efficiency. The design strategy connected with the implementation of renewable energy sources in the form of on-site photovoltaic systems was found to provide the highest reduction in total and operational life cycle GHG emissions, whereas the design strategy related to the use of timber-based materials led to the highest reduction in terms of embodied GHG emissions. Some identified research gaps relate to the lack of holistic life cycle assessment and design strategies for decreasing the environmental impact associated with prefabricated housing units and multifamily buildings in humid subtropical and tropical climates. The identified research gaps were covered in this thesis through the case study research based on the extensive use of building performance simulations (BPS) and life cycle assessments (LCA) with the support of global sensitivity analysis and multi-objective optimisation methods.

The case study research was based on a prefabricated housing unit with a conditioned floor area of 21m2 produced, located, and tested in Shanghai, China, and evaluated the correlation between energy use, indoor environmental quality, and the economics of various energy efficiency strategies in achieving net-zero energy and cost-effective off-grid operation. The design strategies related to relaxed cooling and heating temperature setpoints outside the building occupancy hours, increased thermal insulation thickness, upgrade to triple layer glazing, and implementation of a hybrid ventilation system were found to provide the most significant energy use savings.

The previous research was further developed by comparing different energy efficiency design concepts, including conventional, low-energy, zero-energy, and off-grid design scenarios, and considered the life cycle environmental impacts and the initial investment cost associated with exploring the possible environmental hotspots and trade-offs related to the increased energy efficiency and energy system complexity of the prefabricated housing module.

The life cycle environmental impacts were the lowest for the zero-energy design, with an 86% reduction of GHG emissions compared to the conventional one. The off-grid design presented substantially higher environmental impacts in all investigated categories (by an average of 59%) than the zero-energy design.

Finally, the thesis presents the results of a multifamily building case study located in three warm climate zones in India. The study illustrates the potential and the added value of using innovative approaches combining building performance simulation, life cycle assessment, and life cycle cost analysis with global sensitivity analysis and multi-objective optimisation. The findings of this research identified the most sensitive design parameters influencing life cycle GHG emissions and thermal comfort level, and the most promising design strategies to reduce the life cycle GHG emissions and cost in multifamily buildings located in humid subtropical and tropical climates. It was found that the apartment floor area, equipment loads, windows-to-floor ratio, mechanical ventilation airflow and cooling set-point temperature were the most influential design parameters for the life cycle GHG emissions in the multifamily building design located in each of the investigated warm climate locations. The design strategies, on the other hand, focused on increasing the space efficiency of the building apartments, minimising the area of windows and the solar heat gain coefficient, implementing the hybrid cooling system with the use of ceiling fans and maximising energy generation from the on-site PV system. Implementation of these design strategies provided the best life cycle performance including GHG emissions and life cycle cost.

The main contribution of this thesis is the holistic and combined analysis based on the life cycle approach of residential buildings in humid subtropical and tropical climates at the policy and building design level, which has revealed critical variables and offers practical recommendations and concepts towards the successful mitigation of the effects of climate change in the residential construction sector.