Heating and Cooling an Up-Scale Hotel with Geothermal Energy in Bonn Germany

By Nancy Nies and Paul Gipe


When we think of geothermal energy we immediately have visions of Old Faithful Geyser or the modernistic geothermal power plants of Iceland. But our view doesn’t have to be so limited.

Hot springs have been used to warm aching muscles and bubbling mud baths have been used to cure arthritic joints since before recorded history.

The Romans used geothermal heat wherever they could find it. In cold, damp Britain they built their heated thermal baths, the Aquae Sulis, at, where else, but Bath in Somerset England.

Germany too has a long spa tradition left by the Roman occupation south of the Limes Germanicus.

So it is not too surprising that in Germany’s development of its renewable resources, entrepreneurs would turn to geothermal energy as well as the wind turbines and solar panels now so common.

In the former German capital of Bonn, the up-scale hotel Kameha Grand is both heated and cooled by geothermal heat using a ground-source heat pump.

The site of a former cement plant, the grounds were converted to a hotel and business complex following an architectural competition seeking innovative development of energy efficiency measures. The winner proposed using the unconventional heating and cooling system deriving its energy from groundwater beneath the site near the Rhine.

The six wells in three pairs provide the source water from a depth of 28 m for heating and cooling 80,000 square meters of building area in the €4.5 million development of the hotel complex

On summer days, heat from the building is captured and exchanged with the cooler groundwater. In winter, the process is reversed, and a heat pump is used to warm the buildings.

As a consequence, the hotel doesn’t use air conditioning in the traditional sense and the system only cools the rooms to 18 C (64 F). This is more than sufficient for Europeans, but the hotel staff notes that some American tourists have complained that they can’t lower the temperature further.

During a tour of the geothermal heating system in July 2012, the tour guide suggested that they may simply tell American tourists in advance about the limits of the “climatization” and warn them that if they need it colder than 18 C they need to find another hotel.

The modernistic building uses a dramatic glass façade. While fashionable, the curtain wall heats up the buildings.

The system has been operating has been operating for 2-1/2 years.

Another surprise for North Americans expecting that such an innovative project would be part of some grand government program, the geothermal system was funded privately without subsidies. The owner of the system sells heat and cooling to the building owners.

The system uses internal storage tanks and gas-fired heaters to raise the water temperature for domestic uses and during cold weather.

During the winter, the source temperature of 18 C is heated to 50 C for use in the buildings heating system via a electrically-driven heat pump. The heat pump uses 530,000 kWh annually. Because the heat pump operates on the Carnot cycle, the system generates 2,655,000 kWh of heat.

In the summer, some of the ground water is drawn in at 16 C and use directly. Some stored cold water at 6 C is used with the heat pump to provide additional cooling water. The pumps consume 96,000 kWh for summer cooling.

The system provides 100% of the cooling for the hotel, and 70% of the heating. The project is expected to save 1,700,000 kWh per year over that from a conventional system.

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