In recent years, the concept of energy-efficient housing has gained significant traction. The Passive House standard, known for its rigorous energy-saving measures, has been a front-runner in this movement. However, there is an alternative: Active Homes. These are designed to go beyond the passive reduction of energy use instead of generating energy actively through integrated technologies. But can Active Homes truly be an alternative to Passive Houses?
What is a Passive House?
The Passive House (or Passivhaus) standard originated in Germany in the early 1990s, developed by Dr. Wolfgang Feist in collaboration with Bo Adamson, a Swedish professor. Their goal was to create a building design that would drastically reduce the energy required for heating and cooling, thereby making homes more environmentally friendly and less dependent on fossil fuels. The standard has since gained global recognition, particularly in Europe, where energy efficiency regulations have encouraged the adoption of such designs.
Principles of Passive Houses
At the heart of Passive House design are several core principles that work together to create a home that uses minimal energy while maintaining a comfortable indoor environment. These principles include:
Super-Insulation
Passive houses have exceptionally high insulation levels on the walls, roof, and floor. The insulation acts as a thermal barrier, reducing heat loss in the winter and heat gain in the summer. By significantly limiting heat transfer between the inside and outside of the building, super-insulation ensures that the home remains warm in the winter and cool in the summer without the need for conventional heating and cooling systems.
Airtight Construction
An airtight building envelope is a cornerstone of Passive House design. The structure is meticulously sealed to prevent air leaks, which are common sources of heat loss. Airtightness prevents unwanted drafts and heat loss, ensuring that the conditioned air inside the home stays inside. It also helps to avoid moisture problems that can lead to mould and structural damage.
High-Performance Windows and Doors
Windows and doors in a Passive House are typically triple-glazed and feature insulated frames. They are strategically placed to maximise solar gain during the winter while minimising it during the summer. High-performance windows and doors reduce heat loss and contribute to the home’s overall energy efficiency. They also allow for natural light, improving indoor comfort and reducing the need for artificial lighting.
Thermal Bridge-Free Design
Thermal bridges are areas in the building envelope where heat can bypass insulation, such as at junctions between walls, floors, and roofs. Passive House design eliminates or minimises these thermal bridges. Eliminating thermal bridges prevents heat loss and avoids cold spots on walls and floors, which can lead to discomfort and condensation issues.
Mechanical Ventilation with Heat Recovery (MVHR)
A key feature of passive houses is using a mechanical ventilation system that includes heat recovery. This system continuously exchanges stale indoor air with fresh outdoor air while recovering heat from the outgoing air to warm the incoming air. MVHR systems ensure excellent indoor air quality without compromising energy efficiency. By recovering up to 90% of the heat from the exhaust air, these systems drastically reduce the energy needed to maintain a comfortable indoor temperature.
Performance Criteria
A building must meet strict performance criteria to be certified as a Passive House. These criteria are designed to ensure that the building achieves the desired energy efficiency and comfort level. The key metrics include:
- Space Heating Demand: The building’s energy demand for space heating must not exceed 15 kWh per square meter of living space per year. This is equivalent to about 10% of the energy used by a typical building.
- Primary Energy Demand: This includes all energy used for heating, hot water, and domestic electricity, and it must not exceed 120 kWh per square meter of living space per year.
- Airtightness: The building must achieve an airtightness level of no more than 0.6 air changes per hour at 50 Pascals of pressure (ACH50), which is measured by a blower door test.
- Thermal Comfort: The design must ensure that the indoor temperature remains consistent and comfortable year-round, typically between 20°C and 25°C, without excessive reliance on active heating and cooling systems.
The alternative – Active Homes
Active Homes represent a significant evolution in sustainable housing design. Unlike Passive Houses, which focus on reducing energy consumption to the bare minimum, Active Homes aim to reduce energy use and actively produce and manage energy. The goal is to create energy-positive homes, meaning they generate more energy than they consume over a year. This concept is closely aligned with the growing demand for renewable energy solutions and the push towards reducing our carbon footprint.
Features of Active Homes
Active Homes incorporate various advanced technologies and design principles that work together to create a dynamic, energy-efficient living environment. These features include:
Integrated Renewable Energy Systems
Active Homes are equipped with renewable energy systems such as solar photovoltaic (PV) panels, wind turbines, or even geothermal systems. These technologies are designed to harness natural energy sources and convert them into electricity or heating for the home. By generating their own energy, Active Homes can reduce or eliminate reliance on external power sources, making them more resilient to energy price fluctuations and grid outages. Excess energy can be fed back into the grid or stored later.
Energy Storage Solutions
Energy storage is a crucial component of Active Homes. Battery systems, such as those offered by Tesla Powerwall or other similar technologies, store excess energy produced during the day for use during the night or on cloudy days when solar generation is lower. Energy storage ensures the home can maintain a consistent energy supply even when intermittent renewable generation. This increases the home’s energy independence and reduces the need to draw power from the grid.
Smart Home Technology
Smart home systems in Active Homes are designed to optimise energy use. These systems can automatically adjust heating, cooling, lighting, and appliance operations based on real-time data, such as occupancy, weather conditions, and energy prices. By intelligently managing energy use, smart home technology maximises efficiency and reduces waste. For example, the system might delay running high-energy appliances until solar generation peaks or automatically adjust the thermostat based on the weather forecast.
Advanced Building Materials and Techniques
Active Homes often utilise cutting-edge building materials that enhance energy efficiency and durability. These might include phase-change materials (PCMs) that store and release thermal energy or advanced glazing that adjusts its transparency to control solar gain. These materials contribute to the home’s overall energy performance, reducing heating and cooling demands while increasing comfort. They also contribute to the home’s aesthetic and environmental footprint.
Energy Monitoring and Management Systems
Energy monitoring systems track energy generation, consumption, and storage in real time. Homeowners can use this data to make informed decisions about their energy use, such as when to sell excess energy back to the grid. Real-time energy management allows homeowners to gain greater control over their home’s energy balance. They can identify trends, optimise their energy usage patterns, and reduce their overall energy costs.
Advantages of Active Homes
Energy Independence
Active Homes have the potential to operate independently of the grid or even provide energy back to it. This level of autonomy can be particularly valuable in regions where the energy supply is unreliable or where energy costs are high. Over time, energy independence can lead to substantial financial savings and increased resilience to energy market volatility.
Sustainability and Reduced Carbon Footprint
Active Homes significantly reduces its carbon footprint by generating renewable energy. They contribute to the global effort to reduce reliance on fossil fuels and lower greenhouse gas emissions. This aligns with global sustainability goals, such as those outlined in the Paris Agreement, and can help homeowners contribute to a more sustainable future.
Enhanced Comfort and Customisation
The smart systems in Active Homes can be tailored to the occupants’ specific needs and preferences, ensuring optimal comfort while minimising energy use. Customisation options allow homeowners to create an environment that suits their lifestyle while achieving energy efficiency.
Potential for Financial Returns
In some cases, Active Homes can generate more energy than they use, allowing homeowners to sell excess electricity back to the grid, often through feed-in tariffs or other incentive programmes. This can provide a steady income stream and shorten the payback period for the initial investment in renewable technologies.
