Passive house

Introduction

A Passive house (German: Passivhaus) is a rigorous, voluntary standard for energy efficiency in a building, reducing its ecological footprint. It results in ultra-low energy buildings that require little energy for space heating or cooling. The concept was developed by Dr. Wolfgang Feist and Bo Adamson in Germany in the early 1990s. The Passive House standard is not confined to residential properties; several office buildings, schools, kindergartens, and supermarkets have also been constructed to meet the standard.

Principles of Passive House Design

Thermal Insulation

One of the core principles of a Passive House is superior thermal insulation. High levels of insulation are used to reduce heat loss through the building envelope. This includes walls, roofs, and floors. The insulation materials typically have a low thermal conductivity, ensuring minimal heat transfer. The insulation thickness can range from 20 cm to 40 cm, depending on the climate.

High-Performance Windows

Windows in a Passive House are typically triple-glazed and filled with inert gases such as argon or krypton to improve thermal performance. The frames are also insulated and designed to minimize thermal bridging. The windows are strategically placed to maximize solar gain during the winter while minimizing overheating during the summer.

Airtight Construction

Airtightness is crucial in a Passive House to prevent uncontrolled air leakage, which can lead to energy loss and moisture problems. The building envelope is meticulously sealed, and an airtightness test (blower door test) is conducted to ensure compliance with the standard. The air change rate must be less than 0.6 air changes per hour at 50 Pascals pressure difference.

Mechanical Ventilation with Heat Recovery

A Passive House employs a mechanical ventilation system with heat recovery (MVHR) to maintain indoor air quality while minimizing energy loss. The MVHR system extracts stale air from wet rooms (kitchens, bathrooms) and supplies fresh air to living spaces. The heat exchanger within the MVHR unit transfers heat from the outgoing air to the incoming air, achieving efficiencies of 75-95%.

Thermal Bridge-Free Design

Thermal bridges are areas in the building envelope where heat flow is significantly higher than in the surrounding areas. In a Passive House, thermal bridges are minimized through careful design and construction practices. This includes the use of thermal breaks in structural elements and the elimination of gaps in insulation.

Energy Performance and Certification

A building must meet specific criteria to be certified as a Passive House. These criteria include:

A maximum annual heating demand of 15 kWh/m².
A maximum annual cooling demand of 15 kWh/m².
A maximum primary energy demand of 120 kWh/m².
Airtightness with a maximum of 0.6 air changes per hour at 50 Pascals.

The certification process involves detailed energy modeling using the Passive House Planning Package (PHPP) and on-site verification.

Benefits of Passive House

Energy Efficiency

Passive Houses consume up to 90% less heating and cooling energy than conventional buildings. This significant reduction in energy consumption translates to lower utility bills and a reduced carbon footprint.

Comfort

The superior insulation, airtightness, and ventilation systems in a Passive House create a comfortable indoor environment. The temperature remains consistent throughout the building, and there are no drafts or cold spots.

Indoor Air Quality

The MVHR system ensures a constant supply of fresh air, improving indoor air quality. This is particularly beneficial for individuals with respiratory conditions or allergies.

Durability

The high-quality construction and materials used in Passive Houses contribute to their durability. The buildings are designed to last longer and require less maintenance over time.

Challenges and Considerations

Initial Costs

The initial construction costs of a Passive House can be higher than those of conventional buildings due to the need for specialized materials and construction techniques. However, these costs are often offset by the long-term energy savings.

Design and Planning

Designing a Passive House requires careful planning and attention to detail. Architects and builders must be familiar with the principles of passive design and the specific requirements of the Passive House standard.

Climate Considerations

The design and performance of a Passive House can be influenced by the local climate. In colder climates, additional insulation and higher-performance windows may be required. In warmer climates, shading and ventilation strategies are crucial to prevent overheating.

Case Studies

Residential Buildings

One notable example of a Passive House is the Bahnstadt district in Heidelberg, Germany. This large-scale development includes residential, commercial, and educational buildings, all constructed to the Passive House standard. The project demonstrates the feasibility of applying the Passive House principles on a community-wide scale.

Educational Buildings

The Montgomery Primary School in Exeter, UK, is the first Passive House-certified school in the country. The building features high levels of insulation, triple-glazed windows, and an MVHR system. The school has achieved significant energy savings and provides a comfortable learning environment for students.

Future of Passive House

The Passive House standard is continually evolving to address new challenges and incorporate advancements in building technology. Future developments may include:

Integration with renewable energy sources such as solar panels and wind turbines.
Enhanced materials and construction techniques to further improve energy efficiency.
Expansion of the standard to include retrofitting existing buildings.

References

Feist, Wolfgang. "Passive House Planning Package (PHPP)." Passive House Institute, 2015.
Adamson, Bo. "The History of Passive House." International Passive House Association, 2010.
"Montgomery Primary School Case Study." Passive House Trust, 2012.