Improving the thermal performance of dwellings for carbon positive and healthy homes

Understand the local climate, design for it and build to perform
23 Jun 2019

Energy consumption in the building sector is significant as people are spending a considerable amount of time indoors. The share of the residential sector’s energy consumption is around 11% of the total energy consumed in Australia to fulfil household energy requirements. The largest share of that energy consumption is used to maintain indoor thermal comfort. In future, energy demand for maintaining thermal comfort within a dwelling, particularly for space cooling, will be higher due to global warming (and localised urban heat island effects) if the building design and construction methods are not appropriated to address this requirement urgently.

Decarbonising Australian dwellings would require a significant reduction or elimination of energy consumption for space conditioning. The Australian Government has taken initiatives to improve thermal performance of the building shell through the National Construction Code (NCC). However, the actual energy performance (at post-occupancy stage) of dwellings is often higher than the estimated energy consumption at the design stage. Among many factors which influence space heating and cooling energy consumption in dwellings, the impact of changing climatic conditions cannot be ignored.

This study maintains that understanding the local climate is the significant step in developing energy efficient design and construction methods to address the growing energy needs in a dwelling. This study provides a guideline for improving thermal performance of the dwellings while ensuring that a healthy indoor environmental condition is maintained. Taking a case study of Richmond in NSW, the study will first analyse local climatic conditions (understand the local climate), then it will recommend strategies for a suitable design for that climate (design for the local climate) and finally it will discuss building compliance issues that are important for an energy efficient building (build to perform).

The first part of the study, understand the local climate, highlights the changing climatic conditions. It demonstrates that by comparing the current NatHERS weather file with the future climate scenario for 2030 based on the CSIRO Mk3.5 model. The model takes an A1B (medium CO2 emissions peaking around 2030) of the Intergovernmental Panel for Climate Change (IPCC)’s Special Report on Emissions Scenarios (SRES) with an assumption of a moderate rate of global warming. Climate data is presented in a simplified graphical form which will help inform built environmental professionals about the future climate outlook.

The second part of the study, design for the local climate, outlines adaptive design strategies that would suit future climatic conditions. Future climate scenarios suggest a longer warm period with increased (heat) discomfort conditions and a shorter cool period in Richmond. AccuRate, a NatHERS accredited software, is used to simulate the thermal performance of a dwelling using the current NatHERS weather file and also the future climate scenario. The results of the simulation demonstrate a significant rise in the cooling load and a drop in the heating load. An optimised design for 2030 is developed by upgrading to energy efficient construction systems. However, the high performing design for 2030 does not comply with the current BASIX heating threshold when modelled in the current NatHERS weather file. This highlights the need to revise current legislation to encourage a better design that suits the future climate context.

The third part, build to perform, discusses design and construction issues which are often ignored or get less priority at the design or construction stages. These issues, however, significantly influence overall thermal comfort condtions in dwellings. The issues covered in this part are related to building assemblies, building airtightness, insulation installations, air-conditioning ducting and ventilation in the dwellings.

This study presents an adaptive approach for designing and constructing an energy efficient dwelling with a healthy indoor environment that responds to future climatic conditions embraced by the medium CO2 emissions scenario.

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