If you ask Carol Marra and Ken Yeh, a married couple of architects, where they put the heating and cooling machinery in their house in the Blue Mountains of Australia, a moment of confused silence may follow. And then a burst of laughter.
The 1,600-square-foot residence in the village of Leura, about 90 minutes west of Sydney, has no HVAC system to speak of. When temperatures drop in winter, the couple turn on a Dyson portable electric heater. When temperatures rise in the muggy, buggy summers, “We open a window,” Ms. Marra, 49, said.
Like many energy-efficient buildings, this one is physically oriented to make the most of ambient sunlight. But it is also thermally regulated by a secret sauce. Tucked between joists above the ceilings are packs of BioPCM, an engineered wax that melts as it absorbs heat when the interiors are sultry, and solidifies, releasing warmth, as the rooms turn cold. The low-tech, inexpensive wax is just one example of how the couple, who moved from the United States to Australia in 2002, squeeze efficiency and beauty out of materials and innovations.
Born in Malaysia, Mr. Keh, 53, was a competitive swimmer who was lured to the University of Texas at Austin by the size of its pool. He met Ms. Marra, an Argentine émigré raised in Texas, at the university’s school of architecture. After several years working in Seattle, they found themselves vacationing in Sydney a few months before the 2000 Summer Olympics. The tidied-up host city had never looked better, and they decided to settle there.
