August 13th, 2020
by Christian Matt | Matthias Schuler
This example of a German therapy center including residential accommodation shows how an intelligent concept is capable of cleverly joining ecology and economy. Furthermore, the combined biofuel and cogeneration unit of the neighboring farmer makes even the heating largely autonomous.
he architectural office of Michel, Wolf and Partners (Stuttgart, Germany) has developed a complex of buildings in cooperation with Transsolar Energietechnik GmbH (Stuttgart) featuring an exceptional energy concept. It emerged from an old mansion in the Bergheim district to the northwest of Stuttgart. The plan was to renovate this villa so that it would accommodate a therapeutic institution for a group of just under 40 handicapped people. For accommodating the group residents and for other apartments, a new building was attached to the villa, built by the Dea – conry Stetten. This religious institution wanted a building that would have low energy costs, use renewable energy sources, and still provide high living standards for its residents.
The new extension is a long, three-story, low-rise building whose generous windows provide a notion of transparency. These large windows fulfill two important tasks in our energy concept. On the one hand, they provide high – quality daylight for all the rooms of the new building, thus saving on artificial light and electrical energy. On the other hand, lots of sunlight enters the rooms in winter. This solar benefit additionally lowers energy consumption because heating can be reduced.
The fixed budget for the large low-energy home would provide a feasible solution only if we followed a holistic approach. From the start, all disciplines were included, i. e., structural work, electrical planning, as well as heating, ventilation, and sanitation. For example, the new building rests on a concrete channel instead of individual posts. Half of the channel serves as an earth duct, while the other half provides for technical infrastructure such as waste water, water for domestic use, and ventilation.
The earth duct beneath the building serves as a heat exchanger with the surrounding earth; it supplies the interior with fresh air. In winter, it pre-warms the air naturally before it is brought into the building via a ventilation system. The ventilation equipment provides sufficient fresh air supply to the residents at all times. At the same time, it is equipped with an efficient heat recovery system that greatly reduces the energy consumption compared to a window- ventilated building (Figure 1). Due to very effective thermal insulation and high-quality double-glazed windows in both the new building as well as in the old villa, the buildings lose very little heat in winter, and thus, their demand for heating energy drops.
In summer, thermal insulation and the outside sunshade keep the building cool. However, residents are required to play an active role. Our comfort concept asks them to open the windows themselves during night time in order to cool the massive concrete ceilings and walls through this night air flushing. In addition, the earth duct allows the ground to pre-cool the fresh air before it enters the building on hot summer days.
The Heat Supply
Another distinctive feature is the building’s heat supply: it has no heating unit. Instead, it is connected to the neighboring farm via a local heating pipeline. The farmer living there has installed a biogas system with a cogeneration plant. He runs an agricultural business with approximately 100 cows whose liquid manure delivers part of the fuel’. The remainder comes from organic waste of the sort that collects on a farm. From this, the biogas system produces methane gas (Figure 2). The downstream cogeneration plant generates sustainable electricity and heat from this methane gas.
However, the farmer was initially afraid of the investment costs, amounting to a good quarter of a million Euros, that would be necessary for such a system, in spite of his considerable personal contribution to its construction. Nevertheless, the Deaconry Stetten was able to convince him, since they as operators of the therapeutic institution guaranteed that they would buy the heat they needed from him on a long-term basis. This provides a reliable source of income to the farmer for amortization of his investment costs. It is supplemented with two additional guaranteed sources of income, thus making the project cost-effective. The farmer can feed the surplus electricity from the cogeneration unit into the grid and sell it; and since this electricity is renewable’, it is additionally subsidized in Germany via
the so-called Renewable Energy Sources Act (see also the introductory chapter in this book).
The biogas system features two further secondary benefits. First, it refines liquid manure to high-grade fertilizer that the farmer can distribute on his fields throughout the year. Second, the utilization of methane gas in the biogas system prevents this gas, generally produced by cows, from escaping into the atmosphere as is usually the case in agriculture. Methane is a particularly dangerous greenhouse gas, 20 to 30 times more potent than carbon dioxide.
However, the cogeneration plantt produces more heat than the Deaconry building needs for heating and hot water, particularly during the summer, even though the farmer also uses the heat to cover his private needs. This is due to the high insulation standards in the new residence and the renovated villa. Therefore, the farmer is looking for additional customers that could use the heat locally. In order to be able to guarantee the delivery of heat on winter days, the boiler in his farmhouse was supplemented with an oil reserve so that it can serve as a backup system.
Apart from investment and operating costs, the CO2 balance of the possible solutions was very important for finding the best concept. After the energy consumption for heating and hot water had been reduced by means of the
The local network heating concept with a biogas installation.
THE CO2 BALANCE
The annual greenhouse gas emission balances, expressed in equivalent tons of avoided CO2 emissions, for various spaceheating concepts. The 21-ton contribution shown at the left corresponds to the methane which is not released by the farm from the manure produced, due to the biogas installation.
low-energy concept, the heat required for the therapy center amounted to 161 megawatt hours per year (MWh/a), or, relative to the floor area, 55.5 kWh/m2/a. Here, even after renovating, the consumption of heating energy in the old building is twice as high as in the new building.
For assessing potential greenhouse gas emissions, all supply variants such as biogas, wood pellets, and also natural gas or oil were investigated in terms of their CO2 emissions (Figure 3). Biogas was by far the best alternative; moreover, it even features a negative CO2 potential, i. e., it releases less greenhouse gas as compared to the case that the therapy center had not been built at all. As mentioned, this startling result is due to the fact that without the biogas system, the farmer’s livestock would release methane into the atmosphere, which now is not the case. This reduces methane emissions noticeably, and corresponds to savings of 21 tons of CO2 per year. In the most unfavorable case of an oil heating unit, 57 tons of CO2 per year would be emitted in addition.
The concept that was implemented thus now saves 78 tons of CO2 per year, compared to a conventional building. This clearly shows how effectively such a sustainable neighborhood solution can protect the environment and simultaneously provide an autonomous energy supply. It is a good example of how problems are better solved in cooperation than alone.
The experience of three years of operation has demonstrated that the local heat supply from the biogas installation functions without problems. The heating costs are notably lower than with conventional systems, since they are independent of fossil energy sources (oil, electric power, natural gas).
The example of a therapy building for approximately 40 residents shows the advantages of an intelligent overall concept. The complex comprises an old, renovated villa and an energy-efficient new building. Large windows combined with good insulation use solar heat in winter and reduce electricity-consuming artificial lighting. Via an earth duct, the ventilation system beneath the new building pre-warms the fresh air in winter and cools it in summer. A neighboring farmer provides heating and hot water. He built a biogas system with a cogeneration unit that converts the liquid manure of his cows and other organic wastes into sustainable electricity. The farmer feeds his surplus electricity into the power grid. This concept reduces the total greenhouse gas emissions of the building complex including the farmhouse tremendously. Thanks to subsidies, it has already become economically attractive in Germany.
About the Authors
Christian Matt, born in 1962, studied mechanical engineering at the Institute for Thermodynamics of the University of Stuttgart and wrote his Diplom (Masters) thesis on a solar-thermally operated ventilation system. Since 1996, he has been with Transsolar and has been a project leader there since 2002.
Matthias Schuler, born in 1958, studied mechanical engineering at the University of Stuttgart with a focus on technologies for rational energy use. In 1992, he founded the firm Transsolar in Stuttgart and has been its General Manager since then. He has taught at the Biberach University of Applied Sciences and the University of Stuttgart; After seven years as guest professor, since 2008 he has been Adjunct Professor of Experimental Technologies at the Graduate School of Design, Harvard University, Cambridge MA, USA.
Christian Matt, Transsolar Energietechnik GmbH, Curiestr. 2, 70563 Stuttgart, Germany. matt@ transsolar. com www. transsolar. com
Building Thermography Examined Closely