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Thursday 17. August 2017 16:29Age: 1 year

Conversion instead of replacement – for the energy transition

+ + + Successful integration, architecturally perfect, with outstanding energy values – herein lies the enormous potential of solar energy.

They were celebrating mid-May at Stettbachstrasse 43 in Zürich-Schwamendingen: the reason? Following a substantial conversion, a multi-tenant home – a 1970s energy guzzler – became a plus-energy building with the distinction of being the first Swiss Minergie-A (registered quality label for new and refurbished low-energy-consumption buildings) renewal thanks to solar architecture. And the solar architect who made it all possible was Beat Kämpfen in collaboration with other pioneers in the energy world, not least Ernst Schweizer AG, Metallbau in Hedingen.


A pilot project – accurate, forward-looking and cost-effective: the 1970s architecture was as it were almost totally transported into today's world – only even better. An energy consumption of 30,000 litres of heating oil a year was transformed into an energy surplus. The conversion used no more than about 25 per cent of the grey energy that would have been required to replace the building with a new one of equal size.


And besides the photovoltaics on the roof, it’s the new façade more than anything, which people are talking about. Blending aesthetically into the total picture, it produces heat for hot water and heating rather than electricity, and is wholly cost-effective in terms of renovating a façade.


Beat Kämpfen – Solar Pioneer

Architect Beat Kämpfen had already addressed the issue of façade collectors when converting the residential and commercial building on Limmattalstrasse in Zurich back in 2001.In this case 52 square metres of solar collectors support the wood heating system. The PV canopies shading the windows not only provide protection from the heat in summer but also let the sun reach far into the building in the winter. Many projects by the Kämpfen architect’s firm have followed since, and many of these have won solar awards.


The latest example is now the comprehensive renovation of the multi-tenant home at Stettbachstrasse 43 in Zürich-Schwamendingen. The starting point for the ingenious energy concept was not only the albeit large but closed façade surfaces in full sun but also a disused ventilation shaft for exhaust air in the middle of the building. It was into this that a 19-metre-high solar storage tank was sunk on 26 October 2016: the heart of the new energy centre. Now that the conversion is finished, the building is one of the lighthouse projects in terms of implementing Switzerland’s Energy Strategy 2050.

The background considerations

Coming from the solar collectors on the façades, solar thermal energy has persuasive advantages: in summer, when the sun is high and the heating does not have to be operated at the same time, the yield is higher than in winter when the heating and the domestic hot water systems have to be in operation at the same time. On the other hand, during the winter months when the sun is low in the sky, it shines more directly onto the façade collectors and their desired effect greater as a result, meaning that both the hot water and the heating system can be operated at the same time without any problems. If solar thermal energy is only used to heat domestic water, installing collectors on the roof is not a problem. However, if it has to be used to support the heating system, then, clearly, the right place for it is on or in front of the façade. For an obvious reason: the solar thermal energy is still far more effective than photovoltaics. Moreover, solar thermal energy is gaining new significance when regenerating the heat extracted from the ground by a combination of geothermal probes and heat pumps.


More than just an alternative

Providing a building with sufficient hot water requires a relatively large surface on façade collectors. Therefore, it is important that the owners and residents like them. “There are now many options instead of just black or dark blue solar collectors”, according to Maik Brünig from Ernst Schweizer AG which shares responsibility for the façade with Austrian subsidiary DOMA Solartechnik GmbH. “Bronze, blue, yellow – anything’s possible. ”Hence, more and more options for using collectors as part of the design as well are open to the architects. Although using a lighter colour for the attractive, individual appearance comes at the expense of losing a few per cent of the yield, when integrated into the façade, the collectors can soon recoup some of this loss themselves. In winter, they reduce the transmission heat loss from the walls, thereby contributing to the building’s heat insulation. And another thing – they also protect the building's façade from the effects of the weather.


Ernst Schweizer AG’s contribution to the energy revolution

Ernst Schweizer AG in Hedingen, launched these innovative solar collectors, which have since become extremely popular on the local market, together with Austrian subsidiary DOMA. The expertise that lies behind them is immense – the advantages are huge: the DOMA Flex large wood surface collector is a powerful, highly effective collector. The aluminium absorbers are equipped with a highly selective Microtherm® coating and laser-welded copper pipes, which guarantee optimum output values. Moreover, flexibility is writ large. Whether it is an in-roof or façade collector, in whatever size or form, the DOMA Flex large wood surface collector can be produced and delivered exactly as required in an extremely short time. Not only are over 25 standard sizes made, but also special sizes to suit individual needs. The project on Stettbachstrasse is a good example. 


It shows the successful family owned business Ernst Schweizer AG putting its company philosophy to the test once more. Known for sustainable corporate management, innovative and durable products, low-energy and low-emission manufacturing processes, recyclable materials and a wide range of energy-saving, energy-efficient products, the collaboration between the company and DOMA Solartechnik GmbH is one in which two strong partners have found each other. 


Conversion: starting position and aims

The multi-tenant home housing 48 studio apartments at Stettbachstrasse 43 was built in 1970.A common room and adjoining rooms occupy the ground floor. Although not even 50 years old, in energy terms, the building comes from another time. The concrete construction typical of the times had a system of thermal bridges and no more than minimal insulation. Its energy consumption totalled 30,000 litres of heating oil a year. Structural measures hitherto were limited to maintenance work; the energy consumption was correspondingly high. Hence the building contractor’s decision to carry out a fundamental structural, renewal of the energy system, and, in doing so, to consider ecological aspects. This meant making a decision to ‘buck the trend’ for demolishing buildings built between the years 1940 and 1970 on account of too comfortable a living space, a poor energy balance and the potential to compress.


Reduced energy consumption: measures

Despite a 22 per cent increase in the living space at the same time, the energy consumption was reduced from around 300,000 kWh/a to around 90,000 kWh/a. This means a reduction by a factor of four per square metre of living space. It was made possible by means of solar thermal energy: arranged on the east, south and west façades are 180 m2 of solar collectors. This means the usable solar energy is relatively evenly distributed over the year. The solar collectors are covered with an innovative bronze-coloured glass, which can change to a lighter shade, developed by the Swissinso company and the ETH Lausanne (EPFL) (supplied by Ernst Schweizer AG and its subsidiary DOMA).It is these that characterise the architectural appearance. These types of glass open up new design options to architects, since both colour and format of the coloured glass can be produced in large ranges. Also, stricter quality control measures ensure the solar collectors function perfectly throughout their entire service life – a contribution to the energy revolution, which building owners find easy to make and, in terms of a façade renovation that needed doing anyway, is wholly predictable.


A PV system with a 35.7-kWp output was installed horizontally on the roof. This is expected to produce 33,900 kWh/a. This is enough to operate the heat pump and the ventilation systems, as well as cope with the general electricity demand. The installation of a small battery aims to achieve as a high a domestic consumption as possible. With a surplus of 2,500 kWh per year the energy balance for the building services is positive.


There are concrete troughs above the ground floor to provide green spaces around the building. The plan is to plant trailing juniper bushes here. In addition, climbing hop plants are planted on the large wall surfaces on the east and west façades. Hence, the renovated building provides not only a living space for all the tenants, but also a good habitat for insects and birds, which contributes to a pleasant urban climate.


All in all, a lighthouse project for an architecture that respects the environment has been created. And it was made possible not only by an innovative architect with a network like Ernst Schweizer AG, which seeks and ultimately implements pioneering solutions, but also by a building contractor who takes the needs of a sustainable future seriously.


Media contact

Michael Breuer, Head of Communications

Ernst Schweizer AG, Metallbau
Bahnhofplatz 11
8908 Hedingen, Switzerland

Tel.:     +41 44 763 61 11
Tel. (direct):     +41 44 763 63 59




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Key to pictures: Stettbachstrasse 43 in Zürich-Schwamendingen with the DOMA bronze-coloured, large wood surface collector from Schweizer, © kämpfen für architektur ag

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