Energy Retrofits Protecting the Cultural Heritage in Heidelberg

The old city-center of Heidelberg together with the famous castle of Heidelberg forms a stunning example of medieval and baroque architecture and is the most-visited historical site in the Baden-Württemberg state. The municipal administration is putting great effort into conserving historical city streets and buildings for tourists and visitors, but also into preserving the identity of Heidelberg itself.

Naturally, all buildings consume energy, in Heidelberg primarily for heating. This is why, aside from protecting the cultural heritage, the municipal administration aims to significantly reduce the energy consumption of all public buildings, including those in the historical city centre.

The Palais Graimberg

The Palais Graimberg is located right below the castle of Heidelberg and hosts the offices of the First Deputy Mayor and the Mayor for Environment, Citizen Services and Integration, as well as the City Planning office.

As a result of the energy retrofit, the energy consumption for space heating has been reduced by 50%, from approx. 200 kWh/m² per year down to approx. 90 kWh/m² annually. The measures used to bring down the energy demand needed to be both extensive and invisible, as a standard outer-wall insulation would damage the historical value of the building.

Therefore, the architects, together with the municipal Department for Energy, developed a set of bespoke measures, including: insulation of the top-floor ceiling and the roof without removing the historic brick cover; new tailor-made windows fitted perfectly to the historic appearance, keeping the heat inside of the building.

Instead of adding an external wall insulation, an internal insulation formed of a 5cm-thick layer of cellular concrete was installed, which resulted in halving the heat transfer coefficient for 80% of all walls. This had the highest impact on reducing the heat demand. The replacement of all piping for heat distribution and the renewal of all electrical installations completed the retrofit with additional energy demand reduction.

Three years after the energy retrofit was completed, the measured energy demand for heating of the Palais Graimberg is well below 90 kWh/m², demonstrating the success of the adopted measures. In addition to energy demand reduction, all leaking pipes were replaced, resulting overall the space being transformed into a high-value office space for the administrative staff, as well as offering some of the most representative rooms for high-level meetings available in the city.

The Klingenteichhalle

In 1896, the Heidelberger Gymnastics Club (still existent) employed the architect Wilhelm Mai to construct a new training center for its members. More than 100 years later, this sports hall, the Klingenteichhalle, is still used by many athletes. In 2013, the city administration decided to refurbish the sports hall, as some installations (heating, showers, lighting, etc.) were not safe to use any more and the heating demand had increased significantly.

The architects were facing the same challenges as with retrofitting the Palais Graimberg. An external insulation would destroy the 100-year-old brick-facade, not to mention the beautiful church-like windows. The heat transfer coefficient of these old single-glass windows was 5.0 W/ m²K with much potential for improvement. The new timber-frame windows that were installed during the retrofit were designed as a perfect copy of the old windows, but with a heat transfer coefficient of only 1.0 W/m²K. Together with the internal insulation, the insulation of the top-floor ceiling and the roof and some minor insulation works in other areas, the quality of the building envelope improved significantly. In addition, a ventilation system with heat recuperation further decreased the energy demand and helped to reduce the risks of moisture damage, for instance in the showers area.

The calculations made by the architects assumed that with these measures in place, the heating energy demand would drop to 110 kWh/m² per year – this represents a 50% reduction compared to previous demand. The replacement of an old natural-gas boiler by a combination of a state of the art natural gas-condensation boiler and a wood-pellet boiler further improved the greenhouse gas emissions balance of the overall system. To project was completed with efficient LED-lamps installed instead of traditional light bulbs.