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How Passivhaus Design Reduces Your Carbon Footprint

In recent years, there has been a heightened emphasis on the importance of sustainable living. One of the leading innovations in this area is the Passivhaus design – a rigorous, voluntary standard for energy efficiency in buildings. Passivhaus standards, originating from Germany, are more than just energy-efficient buildings. They represent a holistic approach to sustainable living, designed to drastically cut energy consumption and thereby reduce our carbon footprint. So, how does the Passivhaus design contribute to reducing your carbon footprint? Let’s delve into its core principles.

Embodied carbon in construction

Embodied carbon refers to the greenhouse gas emissions associated with the extraction, manufacture, transportation, and installation of building materials, as well as end-of-life emissions. It encapsulates the carbon footprint of materials from ‘cradle to gate’. As the construction industry seeks sustainable solutions, there’s a growing emphasis on reducing embodied carbon by selecting low-carbon materials, optimising structural designs, reusing existing structures, and considering the entire lifecycle of materials, including recycling or repurposing.

Operational carbon in construction

Operational carbon pertains to the emissions produced during the use phase of a building, primarily from energy used for heating, cooling, lighting, and other systems. This aspect of carbon emissions has traditionally been the focus of energy efficiency and sustainability efforts in construction. By incorporating energy-efficient designs, renewable energy sources, and advanced building management systems, the construction industry aims to minimise operational carbon. Therefore, reducing the overall environmental impact of buildings over their lifespan.

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Space heating and cooling energy demand

One of the hallmarks of the Passivhaus standard is its stringent requirement for space heating and cooling energy demand. For heating, the energy demand must not exceed 15 kWh per square meter of net living space annually or a peak demand of 10 W per square meter. This essentially means that the house retains heat more effectively during colder periods, reducing the need for active heating systems and therefore, energy consumption.

In areas where temperatures soar, the cooling requirements are equally rigorous. The space cooling energy demand is designed to be on par with the heating demands, but with an added provision to handle dehumidification. This ensures that even in warmer climates, the house remains cool without excessive use of energy-intensive air conditioning systems. By setting such strict parameters, the Passivhaus design minimises the need for external heating and cooling sources. In turn, carbon emissions are significantly reduced.

Renewable Primary Energy Demand (PER)

The PER represents a pivotal element of the Passivhaus design. This metric defines the total energy, from renewable sources, consumed in the house for various applications including heating, hot water, and general domestic electricity. The upper limit for this consumption is set at 60 kWh per square metre of treated floor area each year.

What makes this principle particularly significant is its advocacy for a shift from non-renewable, often carbon-intensive energy sources to more sustainable, renewable alternatives. By establishing a clear limit on energy use and focusing on renewables, the Passivhaus design encourages advancements in green technology, such as solar panels, wind turbines, or ground-source heat pumps, integrating them into everyday domestic living. This not only cuts down carbon emissions but also sets the stage for a future less reliant on fossil fuels.

Airtightness for Passivhaus

Airtightness is a pivotal component in the Passivhaus methodology. It ensures that homes prevent unwanted air leakages, which could lead to energy losses. The standard is set at a maximum of 0.6 air changes per hour at 50 Pascals pressure (ACH50), verified through rigorous on-site pressure tests in both pressurised and depressurised states.

This rigorous level of airtightness serves multiple purposes:

  • Thermal Efficiency: By limiting unintended air exchange, homes retain warmth during cold spells and maintain coolness in hotter periods. Overall, this reduces reliance on heating and cooling systems.
  • Consistent Indoor Climate: Airtightness ensures a stable indoor environment, preventing draughts and sudden temperature changes which can be uncomfortable for inhabitants.
  • Protecting Building Integrity: An airtight building minimises moisture ingress. Moisture ingress can lead to mould growth, structural damage, and reduced lifespan of building materials.
  • Economic Savings: Over time, the energy savings from airtight buildings can translate into significant financial benefits for homeowners.

Thermal comfort for Passivhaus

Arguably, one of the most vital principles of the Passivhaus design is ensuring Thermal Comfort. This goes beyond simply maintaining a pleasant temperature; it’s about creating a consistently comfortable living environment throughout the year.

  • Temperature Stability: For residents, this means that no more than 10% of hours in a year should see temperatures exceeding 25°C. This is achieved through a blend of efficient insulation, strategic ventilation, and optimal use of passive solar gains.
  • Human-Centric Approach: Thermal comfort is not just about numbers; it’s about how occupants feel. By keeping temperatures stable, residents are less likely to experience discomfort. Thus, the need for manual adjustments or over-reliance on heating or cooling systems is reduced.
  • Summer Comfort: While much emphasis is placed on keeping homes warm in winter, Passivhaus also ensures that dwellings remain comfortable during hot spells. Through a combination of shading, ventilation strategies, and thermal mass, homes can stay cool even during peak summer.
  • Holistic Well-being: Continuous thermal comfort contributes to better sleep, improved mood, and overall well-being. A stable indoor climate means fewer fluctuations, reduced draughts, and an all-around healthier living environment.
Passive solar gain as a part of thermal comfort

Leveraging natural sunlight is at the heart of the Passivhaus design. This is where Orientation and Passive Solar Gain play pivotal roles.

  • Strategic Orientation: Buildings are oriented to maximise exposure to the sun during colder months. This ensures that living spaces benefit from natural warmth. In contrast, during summer, this orientation, combined with shading solutions, helps in avoiding overheating.
  • Window Placement and Design: Passivhaus homes typically incorporate large, south-facing windows (in the Northern Hemisphere; north-facing in the Southern Hemisphere) to absorb maximum solar energy. Moreover, these windows are often triple-glazed with high-quality frames to both capture and retain heat efficiently.
  • Thermal Mass: Within the building’s structure, materials with good thermal mass (like concrete or brick) are often used. These materials can store heat from the sun during the day. Consequently, they release it during the cooler nights, thus stabilising indoor temperatures.
  • Natural Light: Beyond thermal benefits, optimising natural sunlight reduces the need for artificial lighting, further cutting down energy consumption.
  • Shading Solutions: Overhangs, external blinds, and vegetation can be strategically positioned to block high summer sun, ensuring homes stay cool even during peak temperatures.
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