What is Passive house

Passivhaus or Passive House is an international building standard leader in energy efficiency and indoor comfort. A certified Passive House building guarantees highly efficient buildings with excellent indoor air quality. Passive House was born in Europe in the 1990s, and it has been updated to include essential guidelines for its development in warm climates. The existing number of examples already built and validated by post-occupancy evaluation monitoring, provides a minimum demand for cooling in summer with no overheating.

A Passive House building is one that can guarantee thermal comfort by supplying the energy needed for heating and cooling only through the ventilation system. Therefore, a Passive House building does not require any conventional heating or cooling (although its implementation is fully compatible with traditional construction systems).

The end-use energy demand for heating and cooling systems, DHW (domestic hot water), lighting and electricity should not exceed 120 kWh/m2a.

The Passive House is based on five essential criteria or principals:

  • High level of insulation of the thermal envelope: The space heating energy demand shall not exceed 15kWh/m2 in all climates.
  • High thermally efficient windows and doors: Ug < 0.8W/(m2K)
  • Optimisation of thermal bridges: 0.01W/(mK)
  • High level of airtightness of the thermal envelope: maximum n50 value of 0.6/h (*)
  • Mechanical ventilation system with heat recovery η≥ 75%

Special attention should be given to warm climates in summer by establishing additional solar control strategies.

(*) The air permeability of the building is measured onsite by carrying out a non-destructive test known as the “Blower door” or pressurisation test, where the air flow due to leakage and construction defects is measured under a pressure difference of 50 Pa (approximately equivalent to 30 km/h wind). This value cannot exceed 0.6 h-1 (60% exchange of air volume between the inside and outside at that pressure difference)

Other passive strategies must be applied to these five requirements. The most important ones are related with the solar design principles, such as orientation, thermal inertial of the building materials, shading and solar protection, wind direction, the urban and natural environment or the compacity of the building.

The energy demand during the use of a building is divided into energy demand for heating and cooling, DHW demand, consumption of other electrical energy (without heating or cooling) and additional auxiliary electricity used.

Within this global energy demand, heating and cooling energy demand can be the one with a tremendous environmental impact. Therefore, it is the one with the most significant potential energy savings and the highest potential of reducing carbon emissions into the atmosphere.

The additional investment to complete a Passivhaus certified project can be around 10% – 15% more than an equivalent construction carried out under the minimum building quality standards (CTE in Spain). However, in the medium and long term, it represents a positive investment where the energy savings may be pay off between 8 and 12 years. The long-term net yield is usually between 5 – 8%, depending on the evolution of energy prices.

Passive House in warm climates

It is estimated that in urban areas we spend between 80% and 90% of our live indoors. According to the WHO, 20% of buildings from these countries suffer from the so called “Sick Building Syndrome” (SBS), caused by poor indoor air quality and poor ventilation,

The Passive Houese standard establishes the following parameters to develop a boundary condition regardless of the climatic zone. In the case of Passivhaus Spain (warm-temperate and temperate-cold climates according to areas), an improvement of 60% could be achieved over to the consumption of a new dwelling.

Winter temperatures in warmer climates are milder than in Central Europe (cold climates), so supplying the little heating demand is relatively simple. When exposed to high temperatures, the Passive House standard must be complemented by strategies to dissipate heat: use of the bypass in the heat recovery system, geothermal energy, ground air source exchangers, heat pumps (integrated or not in the ventilation system), or even cooling floors and ceilings.