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commentLearning to Live on Alternative Energy
Three landmark projects show us how to integrate renewable-energy strategies into architecture, without compromising design
The roof consists of a 7.8-kilowatt array of 40 photovoltaic modules provided by Sunpower, as well as exterior canopies consisting of 2 kilowatts worth of translucent thin-film photovoltaics provided by Sunways and sandwiched between plates of glass. The canopies cover porches that counted toward the house’s square-footage allotment, but also provided a buffer for ventilation. Schott amorphous silicon photovoltaic cells, generating 2 kilowatts at peak load, clad the louvers, which were designed with automatically actuated controls that would track the sun to increase output throughout the day. Gehrung says these actuators were so difficult to design and install that she doubts the team would use them again.
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The PV system feeds four separate electrical bus systems for lighting, mechanical systems, entertainment, and controls. The team could document energy production and consumption, as well as indoor air temperature, humidity, and carbon dioxide values through the controls. They used more software programs, such as the Transient Systems Simulation Program (TRNSYS), for analyzing the reversible heat-pump system and the rooftop solar water heaters that helped the project meet its energy goals.
Although each Decathlon project relies on solar photovoltaics for electricity, Gehrung emphasizes her team’s energy-efficiency strategies as the primary motivation for design. Germany’s “Passivhaus” program, which is similar to the U.S. Environmental Protection Agency’s Energy Star rating program, inspired the team to design for local conditions, which in Washington meant a hot and humid subtropical climate. The 19 Darmstadt team members originally wanted to design an all-glass house. Site analysis (the longer sides of the house would face north and south once installed on the mall) indicated the need for less exposure, in order to minimize heat gain without restricting daylighting opportunities. The east and west facades are solid panels finished on the interior with gypboard embedded with phase-change materials (PCMs) that increase the insulation values while providing thermal mass. In this case, the PCMs are paraffin microcapsules called Micronal, manufactured by BASF. Once the temperature of the house reaches around 74 degrees F, the capsules melt and absorb the energy, helping to cool the non-air-conditioned house. In the evenings, the capsules harden to release stored heat. “Sometimes this worked too well,” says Gehrung. “We had so many visitors and we let them stay in the house too long, so we never had enough time to cool the building the way we wanted.”
For a German team designing an American house, some things got lost in translation. For example, the team scored low on the hot-water challenge, since the German showerhead limited the temperature to below the American requirement of 104 degrees F. “In the end, our energy-efficiency strategies helped us win,” says Gehrung, who won’t be involved in Darmstadt’s 2009 entry. “And it was a lot of fun.” Russell Fortmeyer
