Technische Universitat (TU) Darmstadt, Darmstadt, Germany, won first place for its innovative oak louvered home.  (Photos courtesy of Kaye Evans-Lutterodt/Solar Decathlon.)

WASHINGTON - With green building demand increasing, along with the costs of current energy bills, many new energy efficient technologies and applications are hitting the market quickly. At times, however, it can be difficult to balance energy efficiency and savings with usability and practicality. Solar power is one technology that has been around for some time, but its widespread use and application has been hindered. In spite of renewable energy’s slow adoption, however, the U.S. Department of Energy’s (DOE’s) Office of Energy Efficiency and Renewable Energy hosted the 2007 Solar Decathlon at the National Mall, Oct. 12-20. Together with its National Renewable Energy Laboratory (NREL), the American Institute of Architects (AIA), the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), the National Association of Home Builders (NAHB), the U.S. Green Building Council (USGBC), British Petroleum (BP), and Sprint, the DOE chose 20 teams, from around the world, to compete for top honors in this third bi-annual solar housing competition. The event is an international collegiate showdown where student teams compete to design, build, and operate highly energy-efficient, completely solar-powered houses that provide for all the home energy needs of a typical family.


According to the DOE, the three primary purposes of this competition are to educate student participants about the benefits of renewable energy and to challenge them to think in new ways about energy and how it affects everyday life; to raise awareness among the general public about renewable energy and energy efficiency, and what technologies are available to help consumers reduce their usage; and to help move solar energy technologies into the marketplace faster.

Another important outcome of the competition is the research that is yielded from each individual team’s work, experiments, and trials and errors. It is the DOE’s aim to have developed a solar-powered home with a whole house, consistent energy cost of $0.10/kWh by the year 2015.

Second place winner, University of Maryland, College Park, Md., experimented with a liquid desiccant waterfall to help control the humidity in its house.


Each team spends almost two years building a home and preparing for the competition. Once the approximately 800-square-foot homes are built, transported to the National Mall, and set up, there are 10 contests that each compete in to earn points. The architecture category examines a house’s strength, suitability, and appropriateness of materials; its ease of entry, usage, and navigation; and the unusual use of ordinary materials or the use of extraordinary materials. The engineering competition examines the building envelope, indoor environmental control, and mechanical, electrical, and plumbing systems. It also subjects the house to an energy analysis. The market viability contest evaluates whether the house has market appeal and is suited for everyday living. It also examines how easily the house can be built to accommodate a variety of potential homeowners. The communications contest requires teams to communicate the technical aspects of each home, as well as their experiences within the home, to a wide audience through the use of Websites and public tours. The comfort zone contest challenges the teams to maintain a steady, uniform, comfortable temperature and humidity. Full points are awarded for maintaining a 72°F/22°C to 76°F/24.4°C temperature and a 40 to 50 percent relative humidity measurement. There are also the appliances, hot water, lighting, energy balance, and getting around contests. Each is designed specifically to mimic daily real world demands and to test the homes’ ability to meet these demands.

Taking third place, Santa Clara University, Santa Clara, Calif., employed multiple sensors and a data logger to control the environment in its home.


This year’s winners are: first place, Technische Universitat (TU) Darmstadt, Darmstadt, Germany; second place, University of Maryland, College Park, Md.; and third place, Santa Clara University, Santa Clara, Calif. 

TU Darmstadt’s house is a modular domicile that is completely surrounded by timber shutters. The unit consists of three layers. The outer layer is oak louvered frames, which just as with the roof, are equipped with photovoltaic components. It generates electricity and provides protection from overheating. The second layer is the thermal envelope, consisting of highly efficient windows and walls. The third layer is the core in the center of the living space. The team also used four different bus systems, each different by its function, to control multiple systems within the house. The measured values of temperature, humidity, CO2, and current consumption are controlled using EIB, Mod-Bus, and M-Bus systems.

“A solar house is often misunderstood as a house with less comfort,” said a member of the German team. “Our intention was to create a house with a maximum of comfort.”

The University of Maryland house incorporated a backup tankless hot water heater, a liquid desiccant waterfall, an energy recovery ventilator, ductless cooling, and radiant floor heat to ensure the domestic comfort of its occupants.

“For optimal energy efficiency, it is desirable to minimize air leaks through the exterior walls of the house,” noted a Maryland team member. “Good IAQ, however, requires adequate ventilation with outside air. An energy recovery ventilator allows us to maintain superior air quality in the house while minimizing energy losses.”

Santa Clara’s house boasts an “untethered” capability with its photovoltaic panels, high-efficiency inverters, and large battery bank. It also has an integrated controls system that senses indoor and outdoor conditions in order to optimize energy-efficiency and ease of living. There are approximately 30 sensors that collect ambient data on light, temperature, humidity, and CO2. This information is compiled into a data logger, which then communicates with a control point where the information is analyzed and transmitted into a graphic based computer program.

“The controls system can adjust the HVAC system, the electric lighting levels, the electro-chromatic window film, and almost all appliances,” said team Santa Clara. “However, since nobody wants a house that is too smart, the system seamlessly integrates with a full manual override.”


Considering that the energy efficiency and comfort of a home are centered largely on its building envelope and HVAC system, many members of the HVACR industry involved themselves in this year’s decathlon. ASHRAE was a title sponsor of the competition. The association provided standards, as well as guidance through its handbook series, educational programs, research program, and special publications.

“ASHRAE is dedicated to providing more than just minimum energy standards,” said the association. “We are working with the DOE, the AIA, the Illuminating Engineering Society of North America (IESNA), and the USGBC to publish a new Advanced Energy Design Guide series that provides a simple approach for contractors and designers to create advanced energy savings.”

Honeywell, a supporting sponsor, offered participants its non-ozone-depleting blowing agent used in foam insulation, as well as touchscreen programmable thermostats, and other comfort controls and technologies. The company also provided shirts, jackets, and accessories for organizers, volunteers, students, and other personnel who participated in the event.

The International Code Council (ICC), CertainTeed Corp., and Owens Corning were all contributing sponsors. The ICC discounted 22 copies of the complete collection of 2006 International Codes on CD. CertainTeed Corp. sponsored a lunch during the decathlon, and Owens Corning sponsored the printing of the “Energy Savers” booklet that was distributed to the public visitors.

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Publication date:11/12/2007