A Passivhaus is an extremely low energy building. By creating an highly insulated airtight space and utilising MVHR (Mechanical Ventilation with Heat Recovery) technology to manage the airflow through a building, the energy requirements can be efficiently controlled to deliver an extremely quiet and comfortable living environment whilst needing only a fraction – as little as 8% – of the energy required to power a Victorian house.
As well as being low energy, through controlled ventilation a Passivhaus can create an optimum living environment by regulating temperature, humidity and noise levels which creates unparalleled levels of comfort and tranquillity.
The heat and hot water requirements for the house are supplied by low-energy solutions such as Solar Thermal and MVHR (Mechanical Ventilation Heat Recovery) with any remaining electricity requirements either being taken from the grid or (depending on suitability) technologies such as Photovoltaic or wind turbines.
Insulating a building is only one part of making it energy efficient. The thermal bridges must be closed too. A thermal bridge is where heat conducting materials draw heat out of a building either directly such as via a single uninsulated brick wall, or indirectly for example where a wooden joist touches an external wall through a cavity gap. Other examples include metal ties in cavity walls, and other outside connections to internal structures (for example certain types of balcony). In a new build Passivhaus the majority of thermal bridges are designed out at the manufacturing stage. In a period property retrofit, closing thermal bridges can present a real challenge in terms of engineering and ingenuity.
Other than insulation, this is the single most important factor in achieving Passiv standard. Draughts are the enemy of home energy efficiency so creating an airtight building ‘envelope’ by creating a continuous airtight layer throughout the house (for example installing triple glazed windows and doors) is essential. The airflow can then be actively managed via MVHR. An airtight building is also extremely efficient at keeping noise out.
In creating an airtight building ‘envelope’ to prevent heat escape, unless the airflow is actively managed, the interior of the building would become stagnant and humid (witness the common problem with condensation in properties with double glazing but no proper ventilation) An MVHR system delivers fresh air into a building in a controlled way, and uses the heat from the exiting stale air to heat the incoming fresh air. This not only provides ventilation and captures potentially wasted heat energy but also balances humidity levels and filters out dust particles. All this contributes to an environment of unequalled comfort levels with minimal energy usage.