Energy modelling is vital to designing sustainable buildings that consume less energy and contribute less to carbon emissions.
In Australia, Passive Houses are becoming a popular energy modelling solution among architects, builders, and owner-builders to achieve long-term sustainability goals and the collective goal of Net Zero Carbon Emissions by 2050.
However, after the updates of the Australian National Construction Code (NCC) in 2022, the Nathers energy rating scheme must also be considered when constructing new residential buildings.
While both Passive House and NatHERS aim to achieve energy efficiency, there are significant differences. Let’s take a look at these approaches and explore their differences.
What is Passive House Certification?
Developed in Germany in the early 1990s, it’s now widely used in Australia and Europe. This standard is based on sound design principles and calculates the building’s energy performance based on its actual energy consumption data. It aims to construct buildings with minimal energy requirements and maintain comfortable indoor temperatures without conventional heating or cooling systems.
Since the Passive House standard takes a ‘fabric first approach, it has been proven to significantly reduce a building’s energy consumption and contribution to carbon emissions. The Passive House certification process is rigorous and requires attention to all the vital details in the building’s design and construction phase. The certification process involves the following set of performance criteria:
Maximum space heating and cooling demand: The maximum annual energy demand for space heating and cooling can be 15 kWh/m2.
- Maximum primary energy demand: The maximum annual primary energy demand for a building can be 120 kWh/m2.
- Maximum window performance: The windows installed in a building should be designed to minimise heat loss and maximise solar gain.
- Maximum thermal bridging: Thermal bridging occurs due to a break in the building’s insulation layer, allowing heat to escape. You should minimise thermal bridging to achieve Passive House certification.
- Maximum air leakage: The building envelope should be designed to minimise air leakage, with the rate not exceeding 0.6 air changes per hour at 50 Pascals.
- Minimum ventilation: Buildings should have a mechanical ventilation system that can provide fresh air while recovering heat from the outgoing air.
What is NatHERS?
Nathers (Nationwide House Energy Rating Scheme) is an energy rating system developed by the Australian government to measure, understand, and communicate residential buildings’ energy efficiency.
The assessors accredited for NatHERS use computer simulations to determine the building’s energy efficiency based on the following factors:
- Building orientation: The building’s orientation affects the amount of sunlight it receives, impacting its energy consumption.
- Materials: The materials that a builder uses to construct the building affect its thermal performance and energy consumption.
- Glazing: The type of size of windows installed in a building affects the amount of sunlight and heat it receives.
- Insulation: Insulation helps in significantly reducing energy consumption by reducing heat loss and gain through the building envelope.
- Ventilation: Natural ventilation reduces energy consumption by reducing the burden on mechanical cooling and ventilation systems.
- Shading: Adequate shading by using devices like blinds, awnings, and shutters in a building can reduce heat gain and improve energy efficiency.
NatHERS Assessment entails rating the residential buildings on a scale of 0 to 10 stars, with a high rating signifying a more energy-efficient building. If your building achieves a 7-star rating or higher, it will be eligible for government incentives like rebates and grants.
The Australian government initially designed the NathERS scheme to drive innovation, make Australian homes more comfortable and energy efficient, and keep energy costs low.
What are the Key Differences Between Passive House Certification and NatHERS?
Although both Passive House certification and NatHERS aim to promote energy-efficient buildings, these two schemes have some critical differences.
Performance vs. Perspective-based
The primary difference between Passive House certification and NatHERS is the approach to calculating a building’s energy performance. Passive House certification is a performance-based method that has a relatively stricter set of performance criteria. To calculate their energy efficiency, buildings must meet strict limits on air leakage, energy consumption, thermal bridging, window performance, and other factors.
On the other hand, NatHERS is a perspective-based approach that uses a set of standard assumptions and formulas to estimate a building’s energy performance based on many factors. These factors include building orientation, materials, glazing, ventilation, insulation, shading, etc.
Certification process
Passive House certification is based on a rigorous design and construction process, focusing on quality control and attention to detail. Tests and simulations are performed during the certification process to ensure the building meets Passive House performance criteria.
In contrast, NatHers is a standardized rating system that can be applied to many residential building types and designs. Assessors use computer simulations to calculate the building’s energy efficiency, and the NatHERS Certificate specifies the rating based on a standardized set of assumptions and inputs.
Focus Area
The main focus area of Passive House certification is to improve the building’s energy efficiency and reduce carbon emissions. Its certification criteria are designed to reduce energy consumption and promote renewable energy sources.
On the other hand, NatHERS is a broader rating system focusing primarily on energy efficiency. It also considers other factors such as waste management, materials selection, building design and location, and water efficiency.
Cost
It can be more expensive to construct Passive House buildings than conventional buildings because they require high detail and quality control to meet the certification criteria. However, the plus point is Passive House buildings are designed to be highly energy-efficient and, thus, can help you save on energy costs.
In contrast, NatHERS is a more cost-effective rating system that assessors can apply to a wide range of residential buildings. Although NatHERS ratings might not be as stringent as Passive House certification, they still help design and construct energy-efficient buildings.
Concluding Words
Passive House certification and the NatHERS energy rating scheme in Australia are deployed to promote an energy-efficient and sustainable built environment, with buildings contributing to fewer greenhouse gas emissions.
Choosing between Passive House certification and NatHERS Assessment depends on the building project. Passive House design is a more calculated and documented approach, leading to more energy-efficient buildings with higher market values. In contrast, the NatHERS energy rating scheme is cost-effective for constructing energy-efficient buildings.