Nothing about the classic Bavarian structure, rainbow-hued flower boxes, giant cuckoo clock, or towering stone viaduct indicate that the historic is anything more than a traditional space. Located in the Breitnau region of the upper Black Forest, the complex is not just a standard hotel catering to visitors wanting to explore the history and natural beauty of the region. Hofgut Sternen is a marvel of energy self sufficiency.
Tucked behind a handful of doors in the bowels of one of the seven buildings on the property is the hotel’s beating heart and a masterpiece of sustainable engineering. Pipes and exhaust ducts snake along walls and through ceilings, power stations and digital readouts hum, and the complex system powered by water and heat provides 100 percent of the power for the property without pulling a single kilowatt from the local grid.
But energy self-sufficiency isn’t new to the historic 500-year-old hotel (Marie Antoinette once posted up there for a few nights). On the contrary, the compound originally relied upon two dozen water mills along the gorge rivers to power its operations, which included saws, rope mills, and spoon forges (the area was once known as Löffeltal or “Spoon Valley” for the ladle production that occurred there).
It was that history that inspired the Drubba family, currently in its second generation of ownership, to look to water for power once more. “Hydropower has always been used as an energy source [on the property]–and that is what we wanted to do,” says Stefan Hilgers, general manager at Hofgut Sternen.
A goal the team has seen accomplished thanks to an extensive and high-tech interconnected system designed in 2010 that powers and heats the entire property, including 107 guest rooms, the glass blowing studio, and the largest cuckoo clock in the region.
What lies beneath
Of course, none of this is evident as visitors meander around the property, marvel at artists hard at work in the glassblowing studio, peruse the aisles of hand-carved cuckoo clocks, or hike up and down the verdant and shady Ravenna Gorge. On the contrary, it’s only if you sign up for a tour of the on-site power plant that you are led to what looks like an employees-only area, the type of place you’d expect to see workers in jumpsuits coming and going, that you realize what power lies below the surface.
But once the doors are open, all manner of scientific wonder snakes its way through the rooms and narrow corridors, a carefully curated mish-mash of pipes and power stations. At least, to the untrained eye it’s a mish-mash. To Thomas Drubba, hotel owner and occasional tour guide, it’s a perfectly orchestrated balance of give and take, power and pause. It is here that all the wonder of sustainable energy science takes place.
Water and heat become power
It all starts with water. But not with the flowing Revenna or Höllenbach rivers these days.
The property technically still has rights to use the rivers flowing through the gorge, but conservation efforts no longer permit it. So during the design process an alternate solution was presented: the nearby Hinterzarten wastewater treatment plant, which is located higher up the hill.
It’s a delightfully circular system: Hofgut Sternen pumps their wastewater up to the sewage plant, which gets treated, then flows back down via gravity. At this point the water temperature is about 12 degrees Celsius (about 54 degrees Fahrenheit). It passes through a heat pump of sorts, which siphons six degrees of heat to provide 42 kw of electricity or heat for the hotel, and simultaneously cools the water by six degrees so it can be returned to the environment at an appropriate temperature for plants and wildlife.
The process fills two 7,000-liter heat storage tanks, which supplies energy and heat for the whole property. Each building also has a smaller hot water heater pump powered by the large central one.
In the winter, a wood chip power plant—fueled by the leftovers of the woodcutting industry—fills in the gaps. It burns at a low temp, the steam it produces is filtered, and that steam is captured and used to produce energy.
Then there is a spring water catchment system that utilizes the cool water that flows from the surrounding hills to pre-cool things like drinks and air-condition two studios on the property. It functions similarly to a refrigerator: cold spring water is passed through slats and air forced through them cools the room to a comfortable 68 degrees Fahrenheit (20 degrees Celsius).
Even the building itself, including the glassblowing studio, feeds into the power network. “Exhaust air is collected throughout the buildings (restaurant, kitchen, shop, offices), channeled down here and provides us with 54 KW of electricity (or heat)—more than our hydroelectric plant,” says Hilgers. That warm air, once the energy it provides has been captured, is cooled through the heat pump system and sent back out to the environment cooler, another responsible process.
As for other operations, all of the clean water for the bathrooms and kitchen is from a nearby spring. It’s warmed by the same water used for heating the rooms instead of traditional water heaters. “It’s very energy-saving,” Hilgers says. Once that water goes down the drain, it’s pumped backup to the treatment plant and the whole process starts again.
What goes around comes around
It may sound like a complicated and convoluted string of operations, but owner Drubba explains it all with a twinkle in his eye: It’s a whole system of mixed processes that make sense. Indeed, every step has been meticulously crafted for maximum efficiency to not only offer a sustainable place to rest and explore, but to protect the surrounding Black Forest, successfully returning to its renewable roots.
Source : Popular Science