What is Passivhaus?
Passivhaus is an advanced energy performance and thermal comfort standard for both residential and non residential buildings. The concept was inspired by a long history of vernacular buildings around the world which do not require active heating or cooling yet achieve remarkable standards of thermal comfort. Developed and refined by building physicists during the early 1990s in Germany, it is now the fastest growing energy performance standard in world and can be adapted to almost all types of climates.
A Passivhaus may be defined as ‘a building in which a comfortable internal temperature is achieved solely by heating or cooling the fresh air that is introduced in order to meet the occupants’ ventilation requirements.’ Since it is not possible to introduce a lot of heat to a building via the ventilation system alone Passivhaus buildings need to have a very low heating demand.
Characteristics for passivhaus
To operate with only minimal supplementary heating Passivhaus buildings require the following characteristics:
- Unbroken super insulation
- Virtually thermal bridge free construction
- High quality triple glazed windows. These address the first path via which heat is lost from buildings: conduction of heat through the building fabric.
- Very airtight building envelope. This addresses the second path via which heat is lost from buildings: infiltration and exfiltration of air though gaps in the building envelope, otherwise known as draughts.
- Mechanical Ventilation with Heat Recovery. Which addresses the third way heat is lost from buildings: via the deliberate introduction of fresh air and extraction of stale air for the purpose of ventilation. Most of the issues faced by contractors commissioned to deliver Passivhaus buildings come down to being able to accurately cost and reliably implement these five key characteristics of Passivhaus design.
Passivhaus certification requirements
In order to have a building certified as a Passivhaus the following performance criteria must be met:
Building energy performance
- Specific heating demand≤ 15kWh/m2.yr or Specific peak load ≤ 10 W/m2
- Specific cooling demand ≤ 15kWh/m2.yr
- Primary energy demand ≤ 120kWh/m2.yr
Elemental performance requirements
- Airtightness ≤ 0.6 ACH (n50)
- Window U value ≤ 0.80 W/m2K
- MVHR heat recovery efficiency ≥ 75% *
- MVHR electrical efficiency ≤ 0.45 Wh/m3
*Note: MVHR efficiency must be calculated according to PHI standards not manufacturer’s rating
Passivhaus certification is awarded on the basis of ‘as built’ rather than ‘as designed’ performance, therefore pressure test results, commissioning certificates and a record of the build must be submitted before a certificate can be issued.
Excerpt from “Passivhaus primer: Contractor’s guide. So you’ve been asked to build a Passivhaus?” by BRE.