Germany’s building sector produces a third of the country’s total greenhouse gas (GHG) emissions and contributes 40 percent to the total national energy consumption. Therefore, cutting the sector’s emission output has become a key focus within Germany’s mission to achieve carbon neutrality by 2050. Plus-energy buildings present a solution towards fighting climate change as they annually produce more energy than they consume. Furthermore, these innovative buildings enable surplus energy, which has been generated on-site but is not immediately needed by the building itself, to be fed back into the grid or saved through energy-storage technology. This increases the building’s energy independence. Whilst it is debatable whether such buildings will become the norm in the construction arena, they could still increase the marketability of several technological solutions.

Path towards plus-energy buildings and districts in Germany 

Over recent years, German standards for low-energy buildings have greatly evolved. For instance, the “Passive House” has a maximum primary energy demand of 120 kWh/m2 per year (including all household appliances). The thermal performance of the building envelope is maximized and its thermal balance optimized, while ventilation heat losses are reduced through high airtightness and integrated heat recovery systems. Similarly, the net-zero energy building (NZEB) has a primary energy demand of nearly 0 or 0 kWh/m2 per year, with renewable energy sources covering the remaining demand. In fact, this standard will become mandatory among public buildings by 2019 and private buildings by 2021 across the EU under the intergovernmental body’s climate strategy. 

Germany’s first definitions of the Plus-Energy Standard were published in 2011 by the then Federal Ministry of Transport, Building and Urban Development. Since then, these definitions have gradually evolved. In general, the following applies to all plus-energy buildings: both the annual primary energy demand as well as the end-of- year energy demand must be less than 0 kWh/m2 per year. These buildings also stand out in their assessment of the calculation method which is required by the Energy Saving Ordinance (EnEV) – Germany’s regulation on energy performance of buildings. While under EnEV, the guiding audit parameter is primarily the building footprint, for a plus-energy building the complete building plot is acknowledged. Hence, energy generated from sources that are not directly located within the building but on site (e.g. geothermal energy systems or wind turbines) are considered.

Technology supporting the Plus-energy Standard 

Plus-energy buildings acknowledge climatic conditions which critically reduce their energy consumption. Significant amounts of energy generated by heating and cooling systems are conserved through design and construction measures. Thus, compact building design, roofs supporting the installation of PV- or solar thermal systems, and the optimization of passive solar gains through facades and windows facing south should be considered. Dedicated floor plan layouts also contribute to passive energy savings. By minimizing the surface area of walls between rooms with less and those with higher heat demand, transmission heat losses are enormously reduced. Sufficient spaces for building services should similarly be factored into the equation. The building services should also be located strategically to enable short pipe routings which minimize heat losses. 

Cutting-edge technology further cuts the plus-energy building’s energy demand. Examples include energyefficient household appliances, establishment of lowtemperature heating systems, as well as short operation times for heating and ventilation. Additional measures include heat recovery from ventilation, wastewater and efficient room lighting.

Financial incentives and subsidies 

Plus-energy buildings are more expensive to construct than conventional buildings because of their higher technical specifications which must comply with the minimum requirements of EnEV. Presently, no existing program specifically supports the construction of these buildings. However, this area is evolving. In 2011, the federal government introduced the “Efficiency House Plus” program to fund R&D relevant to plus-energy buildings. This program has enabled 37 individual residential projects across Germany – all aiming for the Plus-Energy Standard – to gain financial assistance. 

Germany’s state-owned development bank, the KfW, also offers financial subsidies, such as loans and grants, for constructing new buildings or renewing existing ones which satisfy certain criteria. Buildings are divided into various categories dubbed the “Efficiency House Standards”. The KfW’s Efficiency House Standards are based on a building’s yearly primary energy demand and transmission heat losses. Hence, the “KfW Efficiency House 40” describes a building only consuming 40 percent of the minimum energy limits predefined by EnEV. KfW’s efficiency house categories include KfW 40, KfW 40 Plus, KfW 55 for new constructions, and KfW 55, KfW 70, KfW 85, KfW 100 and KfW 115 for refurbishments. If a project is eligible for a subsidy, the KfW then offers a low-interest loan with a repayment allowance.

The KfW 40 Plus category is the KfW’s most ambitious efficiency standard and offers the highest subsidy amount for private residential buildings. The “plus” category has increased requirements, also including energy storage and building technology. Still, the definitions and standards outlined by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) on the plus-energy building exceed the KfW’s requirements by far. Nonetheless, owners aiming for financial assistance can combine KfW subsidies. 

Furthermore, subnational governments and subnational development banks offer subsidy schemes. For instance, a Berlin program supports energy refurbishments of residential buildings, while Hessen also subsidizes energy efficiency in rental housing construction and renovations. Such subnational schemes not only prioritize environmental factors but also regional aspects. The EU runs dedicated programs targeting the energy performance of buildings. In addition, several commercial banks (e.g. UmweltBank, GLS-Bank, EthikBank) offer low-interest loans targeted at sustainable construction. Such “green banks” supposedly favor investments which are environmentally and ethically sustainable.

Emerging trends 

The plus-energy building concept presents new perspectives on energy supply for urban neighborhood development. This applies to large scale projects in new settlements or existing districts. Working on a larger scale means initial construction costs can be lowered because of economies of scale. Furthermore, surplus energy generated by plus-energy buildings holds vast potential for neighborhoods and districts. Opting to implement on scale also means an entire area can be supplied with decentralized forms of energy, whereas individual buildings can support each other with excess energy.

Energy supply in plus-energy districts can be organized in decentralized, intelligent micro grids. Micro grids in small towns or neighborhoods face fluctuation in their supply and demand for electricity. This occurs when electricity is produced by several renewable energy sources and can affect network stability. To address this problem, an intelligent network management system is required that balances supply and demand. Such a system should also consider weather conditions affecting energy production and demand, additional decentralized battery storage facilities, and intelligent metering systems. 

Feeding energy back into the grid leads to financial benefits for building owners and occupants as a result of a feed-in remunerations scheme which is regulated in Germany by the EEG-Levy. Thus, towns, neighborhoods and individual building owners may profit from this scheme, especially if such enhanced energy efficiency measures reduce their own energy use. In other words, the less energy a building or district requires, the more excess energy can be resold and the sooner initial construction costs of the building, district or infrastructure project can be amortized. 

Furthermore, active and passive technical measures increase energy efficiency and reduce carbon emissions of a plus-energy building during its operational phase. Nonetheless, official frameworks of highly energy-efficient constructions barely consider the embodied energy within a building, nor its full life cycle in their calculation methods. Yet when it comes to technologically advanced constructions, the production, transportation and recycling of materials can reduce large proportions of the total energy performance, in contrast to the energy used for operational purposes. 

The embodied energy of a new building can be reduced by extensive integration of sustainable construction materials recycled at the end of the life cycle. Germany estimates the life cycle of most new buildings at 50 years. Hence, materials which require low amounts of primary energy in their production should be prioritized. Reducing the transportation distances can further cut the embodied energy. 

The certification system of the German Sustainable Building Council (known in German by the abbreviation “DGNB”) considers the embodied energy and recognizes the primary energy demand of construction materials. Regarding the future energy performance calculations required by legal standards, DGNB proposed using CO2 emissions as the target value in the assessment instead of primary energy demand. The “Building Energy Act” (in German “Gebäudeenergiegesetz”, “GEG” in short) is currently in development. The DGNB suggested that rather than comparing the respective building with a reference model, assessment should be carried out with absolute limits on CO2 -emissions of a building. The proposal also includes the integration of a CO2 tax, if target values are not met by a project developer. The current GEG draft law incorporates the mandatory declaration of CO2 emissions in the “Energy Performance Certificate” (“Energieausweis”). The main requirements for the energy efficiency of new buildings in the GEG draft law regard the annual primary energy demand. However, there is ongoing discussion regarding both the utilization of CO2 emissions as a target value and the implementation of absolute limits on CO2 emissions. Hence, these two factors should be officially adopted for new buildings by 2023. The current draft law includes an innovation clause that acknowledges energy performance assessments using absolute limits on CO2 emissions instead of the primary energy demand as the key performance indicator.

Conclusion 

Plus-energy buildings remain on an experimental stage, as this standard has not yet been extensively implemented. Full integration of the standard remains rather cost-intensive, yet the promise of financial incentives and subsidies in the area could provide some relief. Broad dissemination and marketability of technologies would require further financial incentives or dedicated support programs. Tax concessions for private developers could increase attractiveness. Reducing complexity and providing a one-stop solution for plus-energy subsidy programs would further lower barriers. Nonetheless, as ambitious concepts like the plus-energy building gain momentum, the energy performance during operation remains the guiding principle of current and planned legislation. Indeed, only voluntary certification schemes include a life cycle approach. For mandatory standards a paradigm shift would be required. Such an approach would not only include emissions from production and logistics of construction materials, but would also include potential for recycling, after the operational phase of the respective building ends. This would strengthen the likelihood of attaining a carbon-neutral building sector.

Article Resource：Econet Monitor Special Green Building