Author: Ralf Bermich , This article is the paper presented at the 20 International Passive House Conference 2016 in Darmstadt, Germany.

The freight train and switch yard station in Heidelberg was no longer needed when logistical concepts for freight transport changed and it was officially closed in 1997. The US Army had also recently abandoned large areas nearby when they moved their European headquarters away from Heidelberg.

In 2001, an urban planning competition was held, and the proposal from Trojan + Trojan of Darmstadt won the first prize. The concept, which picked up on the geometric structure of the railway lines in designing streets, buildings and greenery, served as the basis for the new Heidelberg-Bahnstadt district covering 116 hectares.

Several years of negotiations and joint planning with the real estate subsidiary of Deutsche Bahn failed to get the development of the new district going. In 2007, dynamic development finally began when the Entwicklungsgesellschaft Heidelberg (EGH) was founded by Sparkasse Heidelberg, the city’s own housing association (Gesellschaft für Grund- und Hausbesitz), and the real estate subsidiary of the Landesbank Baden-Württemberg. EGH purchased the former railway plot and became the development agency and contracting party of the city in the urban development contract for the Bahnstadt. Heidelberg city council’s resolution to develop the Bahnstadt gave the city comprehensive creative scope for development as defined in the German Federal Building Code.

In 2008, urban planning competitions were held for the ‘Wohnen an der Promenade’ residential area along with the special use & science area ‘Campus II’, where dormitories, educational facilities and research-intensive companies were to be located. These two areas constitute the core of the first construction phase at the Bahnstadt (Figure 1); a residents' survey was carried out here, and the results are presented below. Construction of the first residential projects began in 2011, and the first plot was finished in 2012. Marketing of the residential units was very dynamic right from the start. Buyers had very positive views of the Passive House Standard and other sustainability concepts in the Bahnstadt, which were decisive for many of the buyers.

Figure 1: Basic plan for Heidelberg-Bahnstadt. The outlined area shows the residential buildings from the first construction phase, where the survey was carried out (map from the city of Heidelberg based on a draft from Trojan + Trojan)

As an area to be redeveloped and because of its central location, the Bahnstadt is an excellent location for sustainable urban development. In accordance with the city of Heidelberg’s climate protection and sustainability goals, professional concepts for various environmental aspects were worked out.

Because of its proximity to the central train station, the Bahnstadt offers good potential for the use of local and long-distance public transport. Two tram lines will connect Bahnstadt to the rest of the city, and a bike path along the promenade where the freight train line used to be will link the Bahnstadt to adjacent districts without any intersections. A bicycle bridge over the train tracks is planned for connecting to the university and clinic grounds ‘Neuenheimer Feld’. Soil management minimised the amount of soil that needed to be transferred.

Extensive greenery on 66 % of the total roof area simultaneously protects nature, improves the urban climate by means of evaporative cooling and temperature buffering, and the amount of rainwater that enters drainage systems is reduced due to the retention of rainwater. The remaining amount of water that drains off the roofs seeps into the groundwater via special seepage systems (French drain) with biologically active soil layers.

Together with the engineering office ebök, an energy concept was developed for the Bahnstadt [ebök 2007]. Various building standards and heat supply variants for the building structures as envisaged in the master plan were assessed in terms of CO2 emissions and costs to be used as a basis for decisions. On this basis, Heidelberg’s city council decided to make the Passive House Standard compulsory for the entire district, which would also be supplied with district heat from renewable energy. To encourage the sensible use of electricity, a power-saving concept was also worked out [Stadt Heidelberg 2012].

The energy concept was specified as a development goal for the Bahnstadt and was made binding using other legal and contractual instruments. Intensive PR work and sophisticated quality assurance in the planning and construction phases were decisive for compliance with the Passive House standard. The legal instruments and the quality assurance were presented in detail at the 2013 International Passive House Conference [Bermich 2013] [Persch 2013]. The first assessments of heat consumption in the Bahnstadt projects confirmed the successful implementation of the Passive House standard and were presented in detail at the 20th International Passive House Conference by Peper and Persch, as published in the article [Peper 2016]. Here's the link to the corresponding article on Passipedia: Monitoring energy consumption in the new district Bahnstadt in Heidelberg .

In the first quarter of 2015, Heidelberg’s Office of Environmental Protection, Commerce and Energy conducted a survey of all 1,500 households in the Bahnstadt at the time. The households received the questionnaire in the mail, and the survey was also made public in a local newspaper and on the Bahnstadt’s website. The 25 questions were estimated to take ten minutes to answer. Within the deadline of three weeks, 245 questionnaires were returned, equivalent to a response rate of 16.3 %.

When asked about why they chose a Passive House home, 22 % of those surveyed said they did so “out of personal conviction / for sustainability reasons”, which is a very high value for an energy/environmental criterion (Figure 2). Reports from Sparkasse Heidelberg Immobilien also indicate that the Passive House standard was one of the most important criteria in sales and rental discussions. It can be assumed that the energy standard, which is an important image factor for the Bahnstadt, also played a role in the other answers.

Figure 2: Question: Why did you choose a Passive House home? 50% I wanted to live in the Bahnstadt district, 22% for reasons of sustainability, 1% positive experience from friends/neighbours, 27% other reasons

Figures 3 and 4 show answers to the question about satisfaction with living in a Passive House building. On average, 76 % of residents are satisfied or very satisfied, which is a positive result.

Figure 3: Question: On a scale of 1 (dissatisfied) to 10 (satisfied), how would you rate living in a Passive House building

Figure 4: Question: On a scale of 1 (very dissatisfied) to 10 (very satisfied), how would you rate living in a Passive House building

The question about satisfaction combined with information about special features of the Passive House homes reveals that residents who were informed in advance were much more satisfied (Figure 5). This finding shows how important it is to inform buyers and tenants.

Figure 5: Average satisfaction relative to instructions relating to the special features of Passive House homes – question: Were you familiarised with the Passive House features when you moved into your home

Figure 6: Ease of use of the ventilation system (237 answers)

In the past, we were often confronted with concerns that ventilation systems would be too complicated for residents. The answer to the question of whether using the ventilation unit was easy or complicated shows a clear result (Figure 6).

The question about temperatures and air quality in the winter also revealed great satisfaction (Figure 7). Keep in mind that all of the residential buildings from the first construction phase in Bahnstadt have static heaters, generally radiators and some convectors.

Indoor temperatures in the summer were a negative point for 55 % of the residents (Figure 8). The hot summers of the past few years, when Heidelberg experienced tropical nights and overnight cooling was not possible, were one reason. Greater expectations regarding comfort due to air-conditioned workplaces and vehicles probably also led to this result.

But regardless of whether the assessment of temperature as too high was a specific result for the Passive House standard or whether other construction standards face the same, if not more, criticism, there is a need to take greater account of the summer climate in residential buildings in the future.

Figure 7: How do you rate room temperature (top, 238 answers) and indoor air quality (bottom, 241 answers) in the winter

Figure 8: How do you perceive room temperature in the summer (215 answers)

[Bermich 2013] Bermich, R.: Urban development with the Passive House Standard – Heidelberg’s new Bahnstadt district grows dynamically. In: Proceedings of the 17th International Passive House Conference 2013 in Frankfurt, Passive House Institute, Darmstadt, 2013.

[ebök 2007] Baugebiet Bahnstadt in Heidelberg – Städtebauliches Energie- und Wärmeversorgungskonzept, Ingenieurbüro für Energieberatung, Haustechnik und ökologische Konzepte ebök, Tübingen, November, 2007.

[Peper 2016] Peper, S.; Persch, R.: Monitoring energy consumption in the new district Bahnstadt in Heidelberg. In: Proceedings of the 20th International Passive House Conference 2016 in Darmstadt, Passive House Institute, Darmstadt, 2016.

[Persch 2013] Persch, R.: Quality management system Heidelberg’s Bahnstadt Passive House district. In: Proceedings of the 17th International Passive House Conference 2013 in Frankfurt, Passive House Institute, Darmstadt, 2013.

[Stadt Heidelberg 2012] Stromsparkonzept Bahnstadt, Fachliche Erarbeitung ebök, Tübingen, Herausgeber: Stadt Heidelberg, Amt für Umweltschutz, Gewerbeaufsicht und Energie, Heidelberg, 2012.

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