The Heliotrope is an environmentally friendly house designed by the German architect Rolf Disch who also designed the Sonnenschiff (Sun Ship). Three such houses exist in Germany, the first experimental version having been built in 1994 as the architect's home in Freiburg im Breisgau, while the other two are used as exhibition buildings for the Hansgrohe company in Offenburg and a dentist's lab in Hilpoltstein in Bavaria. The most important characteristic of this house is its low consumption due to its ability to rotate according to the sun's position as well as its solar energy production thanks to roof-mounted photovoltaic panels.
The house is designed to face the sun with its triple-pane windows (U = 0.5) during the heating months of the year and turn its highly insulated back (U = 0.12) to the sun during the warmer months when heating isn't necessary. This significantly reduces heating and cooling requirements for the building throughout the year which are provided for by a heat pump, while hot water is provided by vacuum-tube solar panels.
Photovoltaic solar panels with a rated power of 6.6 kW on its roof provide five to six times more energy than the building uses, making the building energy positive (Plusenergiehaus). To further improve energy production, the panels also rotate independently from the building to follow the sun, while being able to adapt its orientation in case of strong winds.
In order to limit water usage, a gray water circuit (for washing dishes and clothes) is used which collects rainwater. Waste water is purified in a cascade plant pool. Natural waste and dweller excrement is dry composted.
One of the main attractions of the house, apart from its low energy needs is its rotating view. As the building turns according to the sun's position, the view changes creating a special experience for dwellers.
The roof deck includes a sun and viewing deck, as well as a garden terrace. The solar panels can be used for sun or rain protection while on the roof terrace.
All floors are accessible from the spiral staircase reducing surface loss through hallways and corridors.
Further potential for this building design includes plans that were drawn up for a possible Heliotrope Hotel. This project currently has no customers but was designed to show that the revolving design can easily be scaled up. The plans for a rotating hotel have surfaced on several occasions although the financing has not yet been available for its actualization.