HENDERSON, Nev. — This experimental dwelling in suburban Las Vegas has all the razzle-dazzle features you’d expect in a show house: a living/dining area with a ceiling that soars 13 feet; an exterior wall that opens to create combined indoor-outdoor space; and a contemporary design with large areas of glass contrasted by earth-tone furnishings. But the gray-skinned, 3,275-square-foot, three-bedroom house in the desert wasn’t designed just to be aesthetically pleasing. The wellness feature is in the walls of Builder Magazine’s KB Home ProjeKt (yes, it’s spelled with a K) so you can’t see it. The house — designed by Manny Gonzalez of KTGY Architecture and Planning in Irvine, Calif., for the 2019 International Builders Show — is equipped with a high-tech system that the manufacturer asserts delivers an impressive level of indoor air quality and water purification and even improves sleep. The system — Darwin by Delos — allows homeowners to enjoy a level of indoor air quality that begins to approach that of hospitals. Darwin is being offered by KB Home in one new development in Irvine on a test-pilot basis. Several luxury-home builders in the United States are installing it. Delos sa...