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Net zero-energy buildings as built reality

The number of net zero-energy or energy-plus buildings worldwide is increasing. It all started off with initial experimental projects that were often conceived as small, energy-independent buildings with no connections to energy grids of any kind. The origins of (net) zero-energy and energy-plus buildings can be traced back to the early 1990s. Since around the year 2000, the number of constructed projects has been rising steadily. These projects now generally involve buildings based on the passive house concept or the Minergie standard. They achieve a neutral or positive energy balance with the aid of cogeneration or solar energy systems. The projects include residential, office and industrial buildings. The first refurbishment projects with the aim of achieving a neutral energy balance began to appear from around 2007 onwards.

We present three projects from Germany here:

  1. A pioneering project: The energy-plus housing estate “Solarsiedlung am Schlierberg” in Freiburg
  2. Climate-neutral kindergarten “Die Sprösslinge” in Monheim
  3. Company headquarters in Berlin with positive energy balance

1. A pioneering project: The energy-plus housing estate “Solarsiedlung am Schlierberg” in Freiburg

The solar housing development “Am Schlierberg” in Freiburg is one of the first energy-plus housing estates in the world. The large surface area of the solar power roofs is particularly striking, and this feature is a significant positive factor in the energy balance. However, the success of this project is essentially based on the systematic implementation of the passive house construction method. An additional factor is the connection to the wood-fired local heating network of Vauban, a nearby district that was planned as a model of sustainable development.

Rolf Disch, the architect and initiator of this project, wanted to achieve even more than the potential offered by the passive house concept that was already popular at the time. Naturally, the development was to be built in an energy-saving manner and supplied using renewable energy sources. However, the buildings were also to provide more energy than that consumed by the buildings and their residents. Rolf Disch coined the term “energy-plus building” here.

The finance concept is an important component of this residential estate, which was built between 2000 and 2006. After all, the solar roofs that are common to all of the terraced houses were to be installed even in cases where one home-buyer was not able to provide the necessary capital for this feature. A number of solar funds – i.e. specific, closed-end property investment funds – provide the necessary finance in such cases. Special agreements were drawn up to clarify the various ownership arrangements for the roofs and buildings.

Concept behind this residential development

Fifty terraced houses are laid out in ten rows of varying sizes, all deliberately facing south, on this 11,000-m² site. The building heights and separation distances between the terraced rows were optimised here in such a way that the sun also shines into the homes in the winter and that the roof surfaces are largely free of shading. These principles combined with the dense layout of the buildings lead to a very uniform overall appearance. However, the homogeneity of the development is counteracted by the different colours of the buildings and the slight angular offsetting of the individual terraced rows.

Architecture

The floor plans of the terraced houses follow the conventional solar house concept: the main living rooms are south-facing, the internal access areas are located in the middle of the buildings, and the so-called service zone – i.e. the kitchen, bathrooms and building services equipment – is north-facing. The buildings have a very compact cubic structure, are designed according to the passive house concept, and include mechanical ventilation with heat recovery and systematic optimal use of daylight.

Energy balance

A solar power system with a total capacity of 400 kilowatts supplies enough electricity to meet the total energy consumption of the residential estate in the annual balance and to feed excess electricity into the electricity grid. The residential estate is also connected to a local heating network that is supplied with heat from a CHP plant. The combined generation of electricity and heat runs on woodchips and natural gas. The primary energy factor for heat thus has a low value of 0.6 and the primary energy requirement for heat is more than balanced by the excess solar power. In this way, a very positive energy balance is achieved on an annual basis.

2. Climate-neutral kindergarten “Die Sprösslinge” in Monheim

Bayer AG had two main aims with this building: This children’s day-care centre in Monheim, close to Leverkusen, should help to improve the work-life balance of company staff while at the same time underlining the company’s commitment in the area of environmental policy. The project was also intended to demonstrate that energy-efficient and environmentally friendly buildings can also be successful from a financial perspective. With this ambitious project, a children’s day-care centre has achieved a positive energy balance for the first time in Germany and has thus more than achieved its stated target of climate neutrality.

An appraisal process was positive in its evaluation of the design by tr.architekten. Further development work on the building, which adheres to the passive house standard, was carried out over the course of the subsequent planning process in line with the “EcoCommercial Building Program” with the aim of achieving a CO2-neutral building. The children’s day-care centre was then constructed in 2009.

The building has optimised thermal insulation, makes systematic use of daylight as a comfort feature, and provides heat using a geothermal heat pump and solar thermal system. The users are impressed: children and kindergarten staff alike are very positive in their evaluation of the overall comfort and indirect daylight. In particular, the thermal comfort is regarded as being very pleasant. This is due in part to the very low amounts of air that enter the rooms in a draught-free manner. Another factor is the presence of large temperature-controlled surfaces that transfer the required heat to the rooms with very low temperature differences.

Architecture

The square building structure in the floor plan also includes a second floor in the northern corner of the building. This second storey only houses certain functional areas for staff. All areas used by the children are located on the ground floor, which has a varied spatial appearance thanks to the differing storey heights used.

Energy balance

As early as November 2010, after 12 months of operation, it was observed that the energy consumption was actually 10 per cent below the planning prediction. The solar power system provided 20 per cent more yield than expected in the same period, which meant that the stated targets of a 100 per cent supply from renewable energy sources and of climate neutrality were easily achieved.

Awards

The building has already received a number of awards, such as the German Federal Ministry of Economics and Technology’s award for “Energy-optimised construction 2009”, the “Auszeichnung guter Bauten (Good buildings) 2010” award from the Association of German Architects and the EU’s “Green Building Award 2011”.

Company headquarters in Berlin with positive energy balance

The headquarters of Solon AG in the Adlershof science and technology campus in Berlin were completed in 2008 and house both administration and production. Solon has committed itself to the principles of sustainable business and the systematic use of renewable energy sources, all of which is not untypical for a company in the solar sector. These principles are also reflected in this striking new building. It uses traditional construction materials and features mechanical ventilation, vacuum insulation, high-tech communication technologies, and heating, cooling and electricity from cogeneration and solar power systems.

It was the client’s wish that the entire facility should have high energy efficiency and be as CO2-neutral as possible. However, the energy requirements of the production equipment have not been included in the emissions balance so far. Architects, energy designers and planning specialists worked together closely during the conceptual development stage to investigate the site conditions and the requirements of production and of the various users of the building in detail. At this early stage, the manufacturers of individual systems and components were involved in order to integrate the potential offered by the wooden construction, which is unusual for office and commercial buildings, and by innovative information and communication technologies into the overall concept in an optimal manner.

Particularly noteworthy is the approach taken for quality assurance and optimisation of operations: a comprehensive monitoring concept is integrated into the building automation and allows for optimisation of the building during ongoing operation.

Architecture

The company’s production and administration areas form two parts of the overall facility and are connected by bridges. The production building was essentially built as a large hall in line with the requirements of the production technology, while the office building was designed with a spatial layout that includes five interior courtyards and is covered by a roof that slopes downward to the south. The building ensemble has a straight edge facing the street and a gently curved transition to the neighbouring park.

Energy balance

In order to decouple electricity generation from electricity consumption at the flexible workplaces that are available, so-called e-shuttles are used that were developed specifically for this project. Their battery units are charged at central charging stations and make it possible to work independently of the electricity supply inside or even on top of the building thanks to these mobile units. There is also a solar charging station in the park behind the building for the company’s eight electric scooters. The energy generated by the “Solar Movers” is also included in the energy balance for the building. They are thus also connected with the building's electricity supply network.

A common technical centre supplies the office and production buildings with heat and cold. The waste heat from the CHP plant is used for heating in winter and to run an absorption cooling system in summer. As the CHP plant runs on biogas, the heating provided is included in the balance with a primary energy factor of 0.7. A second electricity supply network for the technical centre also provides backup supply for production operation. A photovoltaik system with a total capacity of 230 kilowatts is installed on the roof of the building. The excess electricity is fed into the public power grid. The solar power system reflects the integrated approach taken in planning: the company’s own photovoltaic systems are installed only on the edge areas of the roof instead of on the entire roof, in contrast with other comparable designs. This allows for the roof to be planted with vegetation and to be used by the companies staff.
The first approximate analysis of the entire facility carried out in 2008 almost two years after commissioning showed that the energy balance is positive. Balancing was carried out in line with the balance boundaries in the German Energy Saving directive, i.e. excluding the equipment that is mainly associated with production.


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Energy-plus housing estate in Freiburg

Click to enlarge picture + energy balance

Characteristic values for the buildings

Reference area NFA 7,890 m²

A/V 0.56 m²/m³

Construction costs, cost group 300/400
1.940 €/m² (2006)

Residential units 59,
Total residents 170

Energy characteristic values (consumption)

Site energy for thermal heat 
10 kWh/m²a

Site energy for hot water  
26 kWh/m²a

Site energy for electricity 
21 kWh/m²a

Total primary energy consumption 
70 kWh/m²a

Primary energy feed-in (electricity) 
142 kWh/m²a

Energy balance
+ 72 kWh/m²a

 

Climate-neutral kindergarten in Monheim

Click to enlarge picture + energy balance

Characteristic values for the buildings

Reference area NFA 969 m²

A/V 0.56 m²/m³

Construction costs, cost group 300/400
2.200 €/m² (2009)

Residential units 1,
Total residents 71

Energy characteristic values (consumption)

Site energy for thermal heat 
16 kWh/m²a

Site energy for hot water  
8 kWh/m²a

Site energy for electricity 
25 kWh/m²a

Total primary energy consumption 
80 kWh/m²a

Primary energy feed-in (electricity) 
116 kWh/m²a

Energy balance
+ 36 kWh/m²a

 

3. Company headquarters in Berlin

Click to enlarge picture + energy balance

Characteristic values for the buildings

Reference area NFA 9.760 m²

A/V 0.32 m²/m³

Construction costs, cost group 300/400
2.200 €/m² (2009)

Residential units 1,
Total residents 350

Energy characteristic values (consumption)

Site energy for thermal heat 
54 kWh/m²a

Site energy for hot water  
2 kWh/m²a

Site energy for electricity 
40 kWh/m²a

Total primary energy consumption 
25 kWh/m²a

Primary energy feed-in (electricity) 
27 kWh/m²a

Energy balance
Positive (initial estimate)

 

Publications

Here you can find some professional articles:

Net zero energy buildings
A consistent definition framework
Energy and Buildings, Elsevier, 13 S.

Zero Energy Building
A review of definitions and calculation methodologies
Energy and Buildings, Elsevier, 9 S., PDF, 399 kB

Criteria for Definition of Net Zero Energy Buildings
Presentation at the Euro Sun 2010 Conference in Graz
Euro Sun, 8 S., PDF, 126 kB

Load Matching and Grid Interaction of Net Zero Energy Buildings
Presentation at the Euro Sun 2010 Conference in Graz
Euro Sun, 8 S., PDF, 836 kB

Net Zero Energy Solar Buildings
An Overview and Analysis on Worldwide Building Projects
Euro Sun, 9 S., PDF, 391 kB

Net Zero Energy Buildings
Calculation Methodologies versus National Building Codes
Euro Sun, 8 S., PDF, 58 kB

From Low-Energy to Net Zero-Energy Buildings
Status and Perspectives
Journal of Green Building, Volume 6, Number 1, 12 S., PDF, 954 kB

Goal: Zero Energy Building
Exemplary Experience Based on the Solar Estate Solarsiedlung Freiburg am Schlierberg, Germany
Journal of Green Building, Volume 4, Number 4, 8 S., PDF, 339 kB

Ziel Null Energie
Erfahrungen am Beispiel der Solarsiedlung Freiburg am Schlierberg
DBZ 1/2009, Bauverlag, 4 S., PDF, 170 kB