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Project

Germany's Solar Decathlon 2009 SurPLUS House

Credits: ©2009 Technische Universität Darmstadt

At the 2009 Solar Decathlon, Team Germany from Technische Universität Darmstadt started with a "focus on the façade," creating a house that is essentially a two-story cube. The surface is covered with solar cells: an 11.1-kW photovoltaic (PV) system made of 40 single-crystal silicon panels on the roof and about 250 thin-film copper indium gallium diselenide (CIGS) panels on the sides that are expected to produce an incredible 200% of the energy needed by the house. The CIGS component is slightly less efficient than the silicon but will perform better in cloudy weather. The façade's highly insulating, custom vacuum insulation panels plus phase-change material in the drywall maintain comfortable temperatures. Automated louver-covered windows block unwanted solar heat.

 

Germany Solar Decathlon 2009 Deck

Students from Lycee Rochambeau French International School write a report outside Team Germany's solar-powered house during the U.S. Department of Energy Solar Decathlon on the National Mall in Washington, D.C., Tuesday, Oct. 13, 2009. ©2009 Stefano Paltera/U.S. Department of Energy Solar De

The Team
The team is relatively small with only 24 students, mostly architects. But team member Sardika Meyer relates how many others took part. "Even my boyfriend, all the families and friends got involved," she says. "We had so much support; it was really incredible." Team Germany finished first in Solar Decathlon 2007, and the 2009 team has relied on members of the 2007 team for guidance.

The House
The Team Germany philosophy was to "push the envelope with as many new technologies as possible." In particular, the house was designed to maximize PV production and use of the net-metering connection to the electric utility grid on the National Mall. The result is a two-story, cube-shaped building with PV panels on the roof and sides and a single multifunctional living area on the inside. Described by the team as an aesthetic solar design, the house has a bed and other furniture and appliances that fold away or serve multiple purposes.

The Technology
The extensive PV panel deployment is the most notable feature of the Team Germany house, but other technologies include:


• Custom-made vacuum insulation structural panels


• Phase-change material in both walls (paraffin) and ceiling (salt hydrate)


• Automated louver-covered windows


• A boiler integrated into the heat pump system that allows the system to provide domestic hot water as well as heating and cooling.

House Highlights
• A two-story cube shape that provides maximum dimensions and surface area


• A surface area that is almost totally covered with PV panels—single-crystal silicon on the roof, thin-film copper indium gallium diselenide on the sides


• An expected production of twice the electricity needed


• A single multifunctional space inside

Passive Technologies
The engineering of the surPLUShome begins with the idea for the interior design as a single room. This increases the capacity of thermal mass in the space as well as it reduces the necessities for natural and mechanical ventilation or the energy demands for lighting. We adjusted the area of windows and their energy transmission of solar radiation in an early stage of planning. Other parameter was the thermal mass which we increased by latent storage in plasterboards. And we installed a natural ventilation system which allows cross ventilation for high reliability of operation.

To reduce the Transmission heat losses, all opaque walls have a u-value of 0.077 W/m²K in the standard assembly which is about 3 times better than the actual requirements in Germany. The 5 cm thin vacuum insulation panel (VIP) equals a standard insulation of 40 cm. to reduce heat bridges, the VIP layer is mounted continuously all over the building envelope. The building features as well a high insulation in glazing. The triple glazing has a u-value under 0.8 W/m²K.

To reduce the heat losses by air, the building shell is constructed airtight and we analyzed the performance of the shell during construction with a Blower-Door-Test. Overall, these passive measurements of the surPLUShome result in a heat energy demand of 14.9 kW/m²a. Therefore it is a Passive House.

Active Technologies
The building envelope is optimized for energy production, using different kinds of photovoltaic technologies: on the roof high-efficiency monocrystalline photovoltaic (efficiency 18%) is installed, while thin film photovoltaic is applied on the facade. These cells provide extraordinary possibilities of architectural integration, which is one important aim of the energy concept. To provide a more filigree visual expression of the photoactive facade we used CIGS modules with an efficiency of 11 % and a very uncommon proportion of 30 by 120 cm. The façade is therefore able to have cladding and louvers made with the same element. Therefore the facade is able to regulate daylight, solar gains (heating) and cooling demands. It also includes blinds and visors.

Functionality
The surPLUShome features highly efficient appliances in the kitchen as well as for housekeeping. For example we use a dryer with heat pump technology which reduces its energy demand by 30%. All these appliances make it easy and safe to use energy but more important is the building automation as it makes it easy to live efficiently in the house.

The main idea of our building automation system is to provide the inhabitant with information about the current building status and an intuitive control over the buildings equipment as for air conditioning and for energy setup according to the inhabitants needs. This integration of all relevant building elements leads to a more efficient way to use energy and a new lifestyle. Consequently all the multimedia is integrated as well.

We installed a European Installation Bus (EIB) to connect all actors and sensors in the building. And to keep the expenditure for installation in Washington, D.C. low, we integrated small space controllers, which control the actors locally in every building module of the surPLUShome. Only an EIB wire and power cable has to be connected to every module to start operation – it’s really plug-and-play.

To stay close with our design concept we minimized the space used for technical equipment to increase the usable space. So the multifunctional body for example serves as a distributive element for piping and wiring. From there everything spreads through the raised floor level to its destination. It also contains the kitchen and bath, and serves as a staircase up to the 2nd story. With this step we minimized the required space for building service equipment down to 0.7m².

Low – Ex – Technologies
The keyword “LowEx” is formed by a German research initiative, which was founded in the year 2005 in order to bring people together who work on innovations in terms heating and cooling technologies. Exergy –the useful part of energy – allows differing between high quality energies (like current) and low quality energies (like heat). The aim is to reduce “high quality” energy consumption and to use energies more effectively. In building, all controllable technologies generating a “not necessary use” of energy and all technologies using local heat sources have to be counted towards LowEx.

Active Shading
To lower the heating and cooling demands of the surPLUShome the shading influences the solar heat gains of the building. There are two different types of shading systems with different kind of advantages. An exterior louver system (fc-factor = 0.02) integrating the photovoltaic modules of the facade to produce extra energy. The second type is the jalousie-system (fc-factor = 0.08) which is integrated in-between the glass layers to provide accessible openings as for the case of emergency. Both systems are integrated in the building automation and can be set according to the interior needs as well as to external influences (e.g. the sun angle).

Active PCM-System
Every material is capable to accumulate thermal energy and to deliver it again. A phase change material (PCM) is a substance with a high heat of fusion. Thermal energy is absorbed or released when the material changes from solid to liquid and vice versa.

The surPLUShome activates the heat of fusion by using phase change materials and in the cooling ceiling (salt-hydrate). The PCM system has a day-mode, when the interior air circulates through the ceiling and decreases it´s temperature and a night mode, when the cool exterior air blows through the ceiling and discharges the PCM. The PCM can be regulated as a result of being separated from the interior room and controlled by the built in fans. Ventilation flaps allow operating the system with either interior or exterior air. The capacity of the system is equivalent to the energy demand for one day of cooling. We calculated a coefficient of performance of 9 to 15 regarding the ambient temperature.

Heat Pump with Heat Recovery and Water Tank
Due to the German Passive House standard and the resulting small loads the conditioning of the surPLUShome operates by air only. The center of our HVAC is a reversible heat pump which is able to heat and cool the space as one unit. The air source heat pump integrates ventilation compliance, a heat recovery with a coefficient of more than 80%, dehumidification in cooling case and a two layer hot water tank with a volume of 180l. In case of air cooling the as well produced heat is stored in the the hot water tank if possible to increase the exergetic value of operation. The tank also has an electrical immersion heater, whether the capacity of the heat pump is not high enough.


Resources

Solar Decathlon 2009 Team Germany’s Website

Solar Decathlon