Passive House

What is a Passive House?

“A Passive House is a building, for which thermal comfort (ISO 7730) can be achieved solely by post-heating or post-cooling of the fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air.” the exact definition according to the German Institute of Passive Building. The term “Passive house” derives from the German term “Passivhaus”.

A passive house or building is a sustainable construction standard for affordable, high quality buildings offering comfortable and healthy living conditions. It is a building standard that simultaneously offers high energy efficiency, comfort and savings, while at the same time having a very low ecological footprint.

Where does the passive house standard rest upon?

Comfortable and healthy living

The idea rests on designing a building which will maintain a comfortable and healthy interior environment across all seasons of the year, without excess energy consumption. The excellent quality of indoor air, free from pollen and dust particles; the maintenance of desirable levels of humidity and the mild and comfortable indoor temperature across all seasons, are the key features for pleasant and healthy living inside the areas of your house.

The building, which rests on the principles of bioclimatic design, physics and the specifications for energy performance, is constructed in a manner that utilizes solar energy during cold months while protecting the building against heat during the hot ones. Thermal comfort is maximized by taking passive measures, such as insulation, passive use of solar power, internal heat sources, canopies, natural night air conditioning, complemented by high energy efficiency and low energy consumption systems, such as mechanical ventilation fitted with heat recovery.

Environmentally Friendly

Passive buildings have a low environmental footprint, since they utilize extremely low primary energy, due to their minimal energy requirements for heating or cooling, thus leaving sufficient energy resources for all future generations. The additional energy required for their construction (embodied energy) is negligible compared to the energy that they will save later on.

Money saving

Save money by minimizing energy requirements for heating and cooling up to 90% and by decreasing the needs for electricity (primary use of energy) for domestic hot water as well as for all home appliances. The operating expenses for a passive house are minimal, thus expediting the time needed for the recuperation of your initial investment.

The five principles for passive buildings:

The criteria for a passive house are attained by means of careful and smart design and the implementation of the five principles for passive houses: insulation, energy efficient frames and glass panels, air conditioning with heat recovery, the airtightness of the construction and the lack of heat bridges.

All nontransparent structural elements of the building’s exterior enclosure must be very well insulated. A properly insulated building enclosure will keep heat inside the building in winter, while blocking it in the summer. The building’s insulation must have a thermal conductivity (R-) value ≤0,1 W/(mK), while the goal for the enclosure’s U-value is to range from 0,10 to 0,25 W/(m²K).

Building’s airtightness
Uncontrolled outflow (leakage) via openings must be less than 0.6 of the building’s total volume per hour, tested when the building is at 50 pascals of pressure differential (both under pressure and decompression).

Lack of heat bridges
The design and construction of the building’s enclosure aims to minimize heat bridges, thus ensuring a high level of quality and comfort in its interior, in parallel averting damages caused by humidity, while reinforcing the building’s energy performance.

Energy efficient frames and glass panels
The frames’ profiles must be well insulated and fitted with low reflection multi-pane glass panels, argon or other gas-filled to decrease thermal conductivity. In most warm climates, glass panels must have a maximum U-value of 0,80 W / (m²K), an overall frame value, Uw < 1,00 W/(m²K) and total solar solar transmittance g-values (amount of incident solar radiation in the room) around 50%.

Ventilation with heat recovery
Efficient ventilation with heat recovery is key, offering a good interior air quality and energy saving. In passive buildings, at least 75% of the heat from the outflowing air is transferred back to the fresh air, using a heat exchanger. Mechanical ventilation heat recovery systems offer clean air, free from dust and pollen, control humidity and offer maximum energy efficiency due to heat recovery, which may reach 90%.

What are the criteria a building must meet to be considered passive?

A certified building must satisfy the following construction standards, which translate to increased energy savings, good interior air quality and lower operating costs.

  • Energy demands for heating should not exceed 15kWh per net living space square meters (processed floor surface) per year or 10 W per square meter of thermal load. In climates where additional cooling is required during hot months, energy requirements for the cooling of the spaces roughly correspond to the heating ones (15 kWh/m² per net living space per year or 10 W per square meter of cooling load, with additional compensation for dehumification.
  • The total energy utilized for all home applications (heating, hot water supply and electricity consumption) must not exceed 60 kWh per square meter of processed floor area on an annual basis for the Classic category of Passive buildings.
  • With respect to airtightness, the maximum air change rate is limited to n50 = 0,6 air changes per hour at 50 Pascals pressure differential (ACH50), as will be verified by an on-site pressure test (under decompression (discharge) as well as under pressure). The passive house is designed in such a manner so as for most of the external air exchange to be performed using heat recovery ventilation provided by an air-to-air heat exchanger in order to minimize loss of heat (or gain, depending on the climate), so as to avoid uncontrolled air outflow. Even with clear outdoor air, buildings will benefit from mechanical ventilation since it ensures a steady flow of clean air in the interior, preventing problems such as dampness and mildew or radon.
  • Thermal comfort must be satisfied in all living areas both during winter and summer, while temperatures will exceed 25oC for no more than 10% of all hours in a year.

Was is Passive House Certification?

“This building is certified as a passive building” means that, besides the fact that this building has been designed and erected pursuant to the passive house standard, it has also successfully undergone the certification process.

Certification is awarded following a series of comprehensive tests carried out on the building by the network of collaborating bodies and accredited certifiers; tests that are aimed to demonstrate the correct application of the principles of the passive house.

The final and definitive criteria for the certification of passive buildings and passive systems (construction materials) are established by the Passive House Institute in Darmstadt, Germany, under the directorship and guidance of Dr. Wolfgang Feist.

Can I upgrade my building in compliance with the Passive House standard?

Certain parts of the structure will be difficult to change. Foundations, framing, cabling and plumbing installations all constitute core elements of the house.

There are several upgrades and changes that will render a house more energy efficient, offering healthier conditions while also being more durable. By upgrading the windows and the heating/cooling equipment, installing more insulation on the nontransparent structural elements and sealing air outflows (leakages), installing ventilation equipment and utilizing paints with low VOC your house can greatly approximate the Passive House Standard (VOC is an abbreviation for Volatile Organic Compound which are chemicals containing environmentally harmful solvents that evaporate into the atmosphere after the application of dyes or other finishes).

The use of passive house criteria in the renovation of existing buildings leads to extensive improvements with respect to thermal comfort, saving on resources, absence of structural defects and climate protection. A large number of projects have attained a decrease in heat demands up to 90%.

The Passive House Institute (PHI) has developed the EnerPHit standard for this type of buildings, in order to certify the energy modernization of the house using passive components. This requires to either ensure that the maximum demand for heat will be at 25 kWh / (m²a) or, alternatively, the consistent use of passive house systems, in compliance with the PHI certification requirements. Demand for heat is calculated using the Passive House Planning Package (PHPP) as is the quality of thermal protection offered.