ENERGY EFFICIENCY IN BUILDINGS
Europe is leading the way, it’s time the rest of the world caught up!
In light of the growing issue of global warming, a movement towards renewable energy sources and a goal to decrease CO2 emissions, the construction industry needs to better realise its responsibility to play its part. The building sector is responsible for around 30% of total final energy use around the world, therefore the potential for a significant reduction in CO2 is real. In Australia, we suggest there is a need for the government to legislate more strongly in order that the growth in energy efficient buildings grow at an acceptable rate. The Green Star certification is only a voluntary rating system developed by a non-profit industry association (the Green Building Council of Australia (GBCA)), to promote sustainability in the building environment.
According to the GBCA the Green Star certified commercial buildings use 66% less electricity, produce 62% fewer greenhouse gas emissions, use 51% less potable water than an average Australian building. They also recycle over 90% of their construction and demolition waste. Green Star certified buildings similarly exhibit lower operating costs and a higher return on investment4. The government is beginning to take more of an initiative. The Australian Building Code Board (ABCB) has been requested by the Council of Australian Governments to consider changes to the 2019 issue of the National Construction Code (NCC). The changes increased the stringency of energy efficiency provisions for commercial buildings, with further improvements to the NCC for 2022, focusing on residential buildings.
In NSW, a sustainability index BASIX was introduced in 2004 to regulate energy efficiency of residential buildings. However, it is known to being vague, containing many loopholes and deficiencies. It is time that BASIX became more significant to match movement in the commercial sector.
The current definition of energy efficiency by the NCC states:
“Energy efficiency is the prudent, or smart, use of energy resulting from regulatory requirements and voluntary choices in comparison to the amount of energy that would otherwise have been consumed. (…) The desired outcome is using less energy for heating, cooling, ventilation, lighting and other domestic services whilst maintaining expected standards in these areas.”
In simple terms, being energy efficient means using less energy to achieve the same outcomes1.
Classification of Energy Efficient Buildings
There are several types of energy efficient buildings listed in order of their energy usage3:
- Low Energy Buildings: Any building characterised by energy efficient design. The estimated annual energy use is 45-80 kWh/m2.
- Passive Buildings: A building where it’s thermal comfort can be achieved solely by post-heating or post-cooling of the fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air2. The estimated annual energy use is up to 15 kWh/m2.
- Net-Zero Energy Building: Meaning that annually the amount of energy used by the building equals the renewable energy it produces.
- Plus Energy Building: A building that produces more energy than it consumes.
Elements Contributing to Thermal Performance
One of the main contributors to the energy efficiency of a building is the thermal performance of the façade and roof.
Minimising energy loss through the building envelope will have an immense impact on the performance of the building. Particular consideration should be given to:
- The thermal resistance/properties of the materials used.
- Design of joints to minimise thermal bridging.
- Use of high-performance windows in terms of thermal insulation and solar heat gain.
- The inclusion of ‘thermal mass’ in the design of buildings to balance its internal temperature.
Thermal Performance of Traditional vs Modern Facades
Currently, for economic reasons, façade design in high-rise buildings is moving away from traditional materials such as brick and concrete and moving towards lightweight systems such as aluminium cladding.
The weight of a double brick wall is approximately 4-5 kN/m2, while a typical curtain wall system weight is 0.6 kN/m2. This significant weight reduction provides significant cost savings for the main structure and is the reason why the industry is continuing to use more and more lightweight, modern cladding systems.
Although, when considering the thermal performance of the materials, the thermal resistance (a measure of a material’s ability to resist the conductive flow of heat) shows the significant differences between traditional and modern cladding, as seen in the table below:
|R-Value (typical) m2K/W
|Double Brick Wall
|0.5 – 1
|Single pane glass
|0.16 – 0.3
|0.5 – 0.76
|0.05 – 0.1
The weight reduction between traditional and modern cladding systems and the resulting ease of construction, reduces the cost of construction significantly. However, the dramatic differences in thermal performance, as shown above, mean that modern facades need to be designed for energy efficiency to ensure they remain the cheaper option long term.
An array of options is available to improve the thermal performance of modern facades and curtain walls. The glazed areas of a façade can be improved with methods such as, applying low energy coatings or using insulated glass units. The aluminium frames in curtain walls can be designed to be thermally improved by introducing thermal breaks – low thermal conductivity plastics placed in the frame to supress/interrupt the flow of heat.
To determine exactly which energy efficient solutions will be appropriate for any given project, a thermal analysis should be conducted, including optical modelling of the vision glass.
Thermal analysis is therefore highly important for the future of the building industry, particularly due to the increasing use of modern facades in combination with the increasing stringency being applied for building energy efficiency.
Rickard Engineering is one of the few companies that provides thermal analysis design in Australia.
- A more stringent, obligatory energy efficiency regulations need to be introduced for all building types. Currently ‘requirements’ are far too easy to meet and product no positive gain for the environment and building efficiency.
- Energy efficiency regulations need to be the same in all States of Australia. The current system creates confusion, errors and inconsistency for interstate projects.
- Renewable energy sources are a major untapped resource in Australia and need to be utilised.
- Increasing the understanding of thermal analysis and sustainable design is pivotal for the construction industry, particularly with the increased use of modern cladding systems with inherent thermal deficiencies.
- Global warming is a real and immediate issue, which cannot be ignored. However, any and all efforts on behalf of Australia within in the building industry will be in vain if the USA, China and India do not acknowledge the global warming issues and take immediate action. The world’s environment is dying at an alarming rate and will be irreversible if significant action is not taken.
1 Energy efficiency definition by Australian Department of Environment and Energy
2 ISO 7730
3 Approximate energy consumption based on EU’s Energy Performance of Buildings Directive.