Passive House the way forward to reduce climate change impacts

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28 October 2021 | 10 min | Article

Changing building design, construction and operation towards a more sustainable future

Building and construction represent almost 40 per cent of all global carbon emissions^[1]. This consists of operational emissions (heating, cooling and lighting) at 28 per cent and a further 11 per cent from embodied carbon – the materials and processes used during construction.

There is growing awareness of the contribution our built environment makes to carbon emissions and the resultant impacts on climate change, which has raised the question of whether we are doing enough to change the way we design and construct our buildings?

The UN Climate Change Conference (COP26) recognises the important role that the built environment plays in our journey towards zero emissions and through the Building to COP26 Coalition^[2], is calling for urgent action.

Many major asset owners have set net zero carbon targets for their portfolios, driven by stakeholder and investor demands. The role of buildings is proving critical in ensuring these targets are met, through improvements to design, material choices, and technology, and the way we monitor and operate our buildings.

The impacts of climate change through extreme weather events are also a challenge for our buildings. To make them more resilient, we need to take a more strategic approach in their design, construction and operation.

To make the major improvement required to design, build and operate climate-resilient, net zero carbon buildings, we need to change what we design, and how we construct and operate our buildings.

Buildings need to be responsive to their local context and to their function, so that they can operate in the most efficient way possible for the benefit of occupants, owners and the environment. They also need to be resilient to the physical impacts of climate change, such as rising temperatures, fire hazards and extreme cold.

One way to achieve a high level of building performance is by designing and constructing to Passivhaus principles and standards.

What is Passivhaus?

Passivhaus^[3] is a voluntary standard for design and construction that provides a well-established template for ultra–low energy buildings that provide high levels of occupant comfort as well as resilience to future climate changes.

Passivhaus is a verifiable methodology that allows designers and builders to work together to address one of the key challenges we face in the construction industry, namely that we are not very good at designing and constructing well-insulated, airtight buildings. It provides a tried and trusted way of controlling the design and construction process to deliver the comfortable, low carbon, healthy buildings that we need for the climate emergency we are facing.

The first Passivhaus was constructed in Darmstadt Germany in 1991 and there are now over 60,000 Passivhaus buildings throughout the world. Despite being developed initially in cold climates, Passivhaus design principles and standards can be applied to buildings in warmer regions, including Asia and the South Pacific.

For instance, Passivhaus designers in New Zealand work across 19 different climate zones^[3], while in Australia, designers need to contend with eight different climate zones, as identified by the National Construction Code. Each climate zone requires different design approaches. The world’s tallest and largest residential Passivhaus certified building at 26 storeys, The House at Cornell Tech in New York, is located in a region where the average temperatures range from minus 5 degrees Celsius in winter to 30 degrees Celsius in summer. The building uses 60-80 per cent less energy than a conventional building, which translates to planting approximately 5,300 new trees.

In Australia^[4] and New Zealand, a Passivhaus building typically uses 90 per cent less energy for heating and cooling compared to buildings constructed to the current NZ and Australian Building Code minimum requirements. Interest in Passivhaus is growing in the Asia-Pacific region with dozens of projects completed to date and many more in the pipeline.

Any type of building can be designed to Passivhaus standards, including multi-residential, hospitals, universities, shopping centres, schools, commercial offices and more. The standard can be applied to both new and existing buildings.

Passivhaus buildings are:

Insulated and airtight – Through the use of double glazed, airtight windows and continuous wall, roof and slab thermal insulation, ‘air leaks’ in and out of the building are minimised. The insulation also improves thermal comfort and reduces the risk of condensation.
Energy efficient – Passivhaus buildings can save up to 90 per cent in energy costs for heating and cooling, when compared to more traditional construction methodologies and systems.
Comfortable – By minimising ‘air leaks’ and using energy sources inside the building such as appliances and body heat, and externally from solar, the heating and cooling of the building is easier.
Well-ventilated – A mechanical heat recovery ventilation system supplies a consistent flow of fresh, filtered air, that also enables heat from building exhaust systems to be captured and re-used. This constant fresh airflow reduces pollutants, mould and condensation and eliminates uneven ‘pockets’ of cold and/or hot air inside the building.

Levels of Passivhaus certification

Passivhaus has three levels of certification for new buildings: Classic, Plus and Premium.

Passivhaus Classic Certification results in buildings that are highly efficient, while ensuring optimal conditions for human wellbeing. It is a proven methodology for designing, building and verifying building performance against detailed criteria for health (managing moisture, avoiding condensation and mould and ensuring an adequate, continuous supply of filtered fresh air), comfort (maintaining stable indoor air and surface temperatures), and energy efficiency (imposing limits on the energy used for heating, cooling, ventilation and appliances).
Passivhaus Plus Certification results in buildings that meet the conventional definition of zero net carbon – they generate as much energy as they use over the course of a year.
Passivhause Premium Certification delivers carbon positive buildings – they meet all the conditions of Passivhaus Classic, that is, they maintain optimal conditions for human comfort and health, but in addition they use even less energy per square meter per year, and generate more renewable energy on site than they consume in a year.

For existing building refurbishments, an EnerPHit certification can be achieved.

Passivhaus associations around the world, including the Australian Passivhaus Association, the Passivhaus Institute New Zealand and the Passivhaus Institute China, provide detailed information about how to access Passivhaus professionals to assist in achieving certification.

Often, Passivhaus projects will also aim to achieve sustainable building ratings, such as those administered by green building councils, under the umbrella of the World Green Building Council, to recognise and reward designing, building and operating greener buildings.

CASE STUDY

The future of social housing is healthy and sustainable

Kāinga Ora is New Zealand’s largest housing developer and provides rental accommodation for some 187,000 New Zealanders.

Ngā Kāinga Anamata (meaning “Homes of the Future” in Te Reo Māori) is one of several initiatives under its Carbon Neutral Housing Programme. Ngā Kāinga Anamata is a sustainability-innovation pilot programme seeking to resolve many underlying problems with New Zealand’s housing sector including construction sector productivity, energy hardship, sick building syndrome, and climate change mitigation.

The programme involves the design of five almost identical three-level walk-up buildings in Glendowie, in inner East Auckland.

Each building is to be constructed using a different building structural system (precast concrete, light timber frame, cross-laminated timber, light gauge steel frame, hybrid light timber and CLT).

Aurecon is delivering building services (mechanical, electrical, hydraulics and fire protection) and facade peer review across all five buildings, as well as energy performance modelling and passivhaus design services. Ngā Kāinga Anamata was selected to feature in the Built Environment Virtual Pavilion at the COP26 UN Climate Conference in Glasgow in November 2021 as one of 17 projects from around the world demonstrating opportunities for sustainability in the built environment.

The key to delivering net zero carbon all-electric buildings cost-effectively is to use the Passivhaus principles and methodology during both design and construction to deliver a continuously insulated airtight envelope (See Figure 1).

Figure 1. Five principles govern Passivhaus

The five Passivhaus principles are:

Thermal insulation: Insulation in walls and ceilings that is appropriate for the climate zone is required to ensure there is sufficient separation between the outdoor and indoor environments.
High performance windows: Windows are the greatest source of heat/cold loss and gain so also need to provide good insulation by being low-emissive double or triple glazed with thermally broken or non-metal frames. Drawing on the principles of passive solar, they should also be orientated to capture winter sun and summer shade and breezes.
Mechanical Heat Recovery Ventilation (MHRV): An MHRV system draws filtered outdoor air into the building and removes stale air to the outside, transferring energy between the two air streams, resulting in a constant flow of fresh, filtered, tempered air. Passivhaus standards consider balanced ventilation systems, sized for the least amount of outside air to meet the needs of the occupants, which further minimises construction and operational costs. This doesn’t mean windows can’t be opened; it just provides the option to not open them on excessively hot, humid, windy days, while still enjoying fresh filtered outdoor air.
Airtightness: ‘Leaky’ buildings through gaps and cracks in the building envelope not only make the indoor environment uncomfortable but also leads to higher energy bills. Creating an airtight envelope ensures that only fresh filtered air is inside the building, below 0.6 air changes per hour (ACH) for new builds or 1.0 ACH for retrofits, to achieve certification.
No thermal bridges: To avoid thermal bridges, which are pathways between the inside and outside of buildings through which heat can move easily, a number of elements need to be considered: is the insultation continuous; are windows and frames enabling heat/cold exchange; are materials being used that are highly conductive (eg metal as opposed to timber). Appropriate thermal breaks can remove the possibility of condensation that can lead to mould and indoor air quality concerns.

Testing, testing: how responding to climate change will make our world quieter

CASE STUDY

The largest Passivhaus-certified building in the southern hemisphere

Large scale-buildings using Passivhaus principles, such as Monash University’s new Woodside Building for Technology and Design, which was engineered by Aurecon, as part of the project team of Grimshaw Architects, Monash and Lendlease, is an excellent example of designing and building with climate change mitigation at its heart.

Monash Woodside is the largest Passivhaus certified building in the southern hemisphere, and the largest Passivhaus certified education building in the world. It’s been designed to be all-electric and net zero carbon in operation and it was delivered for a small premium on a conventional construction budget.

The Woodside building was selected to feature in the Built Environment Virtual Pavilion at the COP26 UN Climate Conference in Glasgow in November 2021 as one of 17 projects from around the world demonstrating opportunities for sustainability in the built environment.

Passivhaus – not an afterthought

Designing to Passivhaus principles needs to occur at the very beginning of the design process and incorporate an integrated approach from all project partners.

Architects, engineers, contractors and sub-consultants need to be committed to achieve the high-performance standards required to reach Passivhaus certification, and advice from a certified Passivhaus designer is required to ensure the building meets all requirements. While this may seem complex, Passivhaus is a simple approach that creates a more stable environment, rather than incorporating more energy intensive means to regulate air quality and temperature.

In the long-term, a Passivhaus building will be more efficient, less expensive to heat and cool, more comfortable for occupants and more resilient to extreme weather events.