Enlarge this picture Team Boston member Clay Larsen installs a rainwater-capturing sculpture that will deliver water to a fish pond during the U.S. Department of Energy Solar Decathlon 2009 on the National Mall in Washington, D.C., Oct. 06, 2009. (Credit: Stefano Paltera/U.S. Department of Energy Solar Decathlon.)

The fourth Solar Decathlon took place on the lawn of the National Mall in Washington just a couple weeks ago. As I was gathering information to write an article on this year’s contest, it struck me how very few of the solar homes used solar radiant heating systems.

Out of 20 teams, seven had radiant heating and/or cooling systems (six under-floor and one ceiling application). Compare this to the first contest in 2002, where five homes used radiant under-floor heating.

Several homes used geothermal or ground-source heat pump systems to heat and cool the houses, although geothermal had to be simulated since teams couldn’t drill 500-foot holes in the National Mall ground.

Each team is challenged to design, build and operate the most attractive and efficient solar-powered house. The overall winner of this year’s contest was Team Germany from Darmstadt, Germany — the team’s second victory after winning the 2007 competition. The University of Illinois took second place and Team California (Santa Clara University and California College of the Arts) took third place.

Interesting Elements

Enlarge this picture Visitor Clara Duffy touches a passive-heating water wall made of recycled plastic water bottles in the University of Arizona's solar-powered house during the U.S. Department of Energy Solar Decathlon on the National Mall in Washington, D.C., Oct. 17, 2009. (Credit: Stefano Paltera/U.S. Department of Energy Solar Decathlon.)

You don’t heat too much about radiant cooling, but Team California (also winner of the Architecture contest) decided to incorporate it in its Refract House. The team used a solar thermal absorption chiller to supply the radiant cooling panels; waste heat from the chiller preheats water for the solar hot water system.

Radiant in-ceiling water pipes for heating and cooling are part of the University of Puerto Rico’s house. The system is designed to operate at slightly cooler than the ambient temp to avoid condensation.

The University of Minnesota team’s house uses solar hot water for domestic water and radiant under-floor heat, but the solar water heating system is used in the summer to recharge a desiccant system that efficiently pulls moisture out of the home’s air to maintain humidity and comfort levels. Iowa State’s Interlock House had a similar system.

Rainwater collection was integrated into Team Boston’s (Boston Architectural College and Tufts University) Curio.House, the University of Wisconsin-Milwaukee’s Meltwater house and the University of Puerto Rico’s home.

Virginia Tech incorporated a rainwater collection system and a grey water filtering system. The roof is sloped to collect rainwater that is filtered for potable water, while grey water is goes through a series of bio-filters in the surrounding landscape where it is cleaned for nonpotable use.

The University of Illinois at Urbana-Champaign won the hot water contest with its hot water system heat exchanger. The “shower tests” requires systems to deliver 15 gallons of hot water in 10 minutes or less.

Penn State installed water bags to provide thermal mass, absorbing heat through the day and releasing it at night. The bags were not filled until the house got to its site to reduce fuel use.

The “water wall” at the University of Arizona’s SEED[pod] home helps reduce heating and cooling needs. One of the passive energy and comfort strategies used in the house, the vacuum-formed clear plastic water wall acts as a “heat sink” by deterring heat from entering the house during the day and releasing it slowly after the sun goes down.
It sure is an innovative way to keep plastic water bottles out of the landfill…