Passive House + renewables - the perfect NZEB

Since the ratification of the Energy Performance of Buildings Directive, the 28 member states have been working to develop their own definitions of Nearly Zero Energy Buildings, which will be required as of 2020. The Passive House Standard already offers a highly efficient and economically viable solution that can be effectively combined with renewable energy.

In the current debate about the introduction of so-called Nearly Zero Energy Buildings, reference is made to a range of energy efficient construction concepts: Passive Houses, green buildings, solar houses or sustainable buildings, to name just a few. All these concepts are fundamentally convincing in their own way, as proven by the large number of exemplary projects around the world. With its clearly defined standard and general applicability, Passive House stands out from other concepts.

Passive House - the perfect NZEB

Based on consistent compliance with several performance related criteria, the Passive House Standard has proved itself in practice in building types ranging from houses to schools, supermarkets, offices and apartment buildings. In addition to its high efficiency requirements, this standard is also impressive with regard to its excellent cost-benefit ratios when taking into account the lower overall energy costs. The potential use of renewable energy further reduces the already low CO2 emissions. Passive House thus fulfils the requirements of the EU Energy Performance of Buildings Directive in every possible respect, thereby forming the ideal basis for Nearly Zero Energy Buildings.

An overall energy performance standard, the Passive House Standard is not limited to any specific construction design or building type. Any experienced architect can design a Passive House building in line with his or her own creativity. What matters is the quality of the details. As a result, the building owner will have an energy efficient building that is both cost-effective and comfortable.

Heat that is not lost in the first place does not have to be actively supplied. This is the key principle of the Passive House Standard and is mainly achieved by means of a well-insulated building envelope. "Passive" sources such as the sun shining through the windows, as well as internal heat sources such as heat from people and appliances, suffice to heat the indoor space. Added to this is a ventilation system in which heat is recovered from the extracted air.

In this way, a Passive House consumes about 90% less heating energy than a conventional building and more than 75% in comparison to an average European new build. This standard thus makes a significant contribution to the energy revolution and to climate protection. A Passive House is also an attractive investment for building owners: extra costs incurred in the construction phase are amortised after a few years due to saved energy costs. Even after this time, heating and cooling bills will be a tenth of what they are in "normal" buildings. Passive House occupants are thus less dependent on future energy price developments.

The first Passive House was built in 1990 in Darmstadt (Germany). Systematic measurement of this pilot building’s consumption data provided evidence that the previously calculated energy savings were achieved in practice. Different types of buildings based on the Passive House principle where then built in the framework of further research projects, ranging from schools and offices to swimming pools and supermarkets, all built to the Passive House Standard. The following years also showed that this standard is not only applicable and successful in Central Europe, but also in all other climate zones throughout the world.

Five key factors

The general applicability of the Passive House Standard has led to a huge increase in its dissemination internationally in recent years. Of course, the exact implementation details depend greatly on the respective project and location. The technical challenges that must be mastered in the case of a supermarket with energy-intensive refrigeration systems are completely different to those of a conference building that is only used occasionally, but that is full when in use. A home in Northern Scandinavia must be planned differently to a home in the Mediterranean. The fundamental principles of the standard, however, remain the same regardless of whether these are applied to new builds or energy efficient retrofits in accordance with the so-called EnerPHit Standard. The five key factors for consideration in all cases are:

1) An optimal level of thermal insulation. This provides for excellent thermal protection of the building envelope and is essential to achieve high levels of energy efficiency, as most of the heat in conventional buildings is lost through the exterior walls, roof and floor. This principle is reversed in the summer and in warmer climatic zones: alongside external shading elements and energy efficient household appliances, thermal insulation ensures that heat remains outside, keeping the inside pleasantly cool.

2) Thermally insulated window frames with high quality glazing. Such windows, typically with triple-glazing, “trap” the sun’s heat during the cold winter months. South-facing windows in particular direct more solar energy into the house than the heat they release towards the outside. During the warmer months, the sun is positioned higher in the sky so that less heat is trapped. Still, external shading is important to prevent any overheating.

3) Thermal bridge free construction. Heat will travel from a heated space towards the cooler outside, following the path of least resistance. Thermal bridges are weak points in a structure that allow more energy to pass through than might be expected. Avoiding thermal bridges in building design is thus a great way to avoid unnecessary heat loss. Careful planning, especially for connections between building components, intermediate ceilings, and foundations, is essential.

4) An airtight building envelope. An airtight envelope that encloses the whole interior space prevents energy loss, moisture-related structural damage, and draughts. To achieve this, Passive Houses are designed with an uninterrupted and continuous airtight layer; special attention must be paid to junctions and connection details.

5) Ventilation with heat recovery. Heat recovery ventilation ensures a plentiful and consistent supply of fresh, clean, dust and pollen free air while reducing energy losses. Up to 90% of the heat from the extracted air can be recovered via heat exchange. These systems are usually very quiet and easy to operate.

Thermal comfort

Passive House is not just an energy-saving standard; a central component of the concept is the high level of thermal comfort. Throughout the building, indoor temperatures remain constant and comfortable year-round, even without floor heating or radiators near the windows.

Passive House design

While the concept behind the Passive House Standard may be straightforward, great care must be taken during design and construction to achieve the desired results. Each Passive House project should be guided by an experienced expert right from the design phase. The Passive House Planning Package (PHPP), long internationally established as the premier design tool for Passive Houses and other energy efficient buildings, enables experts to accurately predict the effects of design changes on annual heating demand and other important characteristic values.

Quality assurance through certification

Passive House certification further ensures both high quality and that the designed energy performance is delivered in practice. Certification is either carried out by the Passive House Institute itself, or by an internationally accredited Building Certifier. Through certification you can be sure that the delivered energy performance and quality is as promised.

Integration of renewables

Passive House can be combined with all kind of renewables. To mention only a few: PV and solar panels for domestic hot water, heat pumps with soil heat exchanger or ground water, all kind of biomass boilers, connection with district heating based on renewable energy, etc., the technology is completely independent from the kind of energy supply. In the last version of the PHPP (Passive House Planning Package special attention has been put on the integration of renewables. Also in the new Passive House classes (Classic, Plus and Premium) the supply with energy from renewable sources are key element. Clearly focussing on 'energy efficiency first' and then use renewables Passive House makes the Energiewende possible.