Rosenstein Quarter in Stuttgart

Modern residential quarter with innovative energy system from Viessmann

Siedlungswerk GmbH Wohnungs- und Stäädtebau is implementing the development and construction of 500 apartments in the Rosenstein Quarter in Stuttgart, which will be supplied with heating, cooling and electricity by a multi mode energy system from Viessmann.

The first construction phase on the site of former pharmaceutical company Haidle & Maier, known as the "Schmidtgen-Areal" in the new district of Stuttgart-Rosenstein, was completed in 2017. The building plot on Nordbahnhofstraßße and Eckartstraßße covers an area of approx. 8600  m². Here, 125 residential units with a total living space of around 11,400 m² were built to KfW Efficiency House 55 standard.

The area, which is in the immediate vicinity of the S21 main line station, is located directly next to the park-like Pragfriedhof and close to the new European Quarter and the "Rosenstein development area", which was previously the site of the now vacated railtrack areas. From there, it's a short walk to the Schlossgarten. The light railway stops at the complex and takes residents directly to Schlossplatz, right in the urban centre of the state capital, in a matter of minutes.

The architectural competition held in spring 2012 for the first part of the development was won by Ackermann+Raff from Stuttgart and Tüübingen. Directly adjoining to the south, on the former Staiger site (on the corner of Nordbahnhofstraßße and Friedhofstraßße), was the location for Siedlungswerk's second construction phase. This was implemented by the winner of a second architectural competition, KBK Architekten GmbH Belz Lutz from Stuttgart, with construction starting in 2018.

Perfectly coordinated energy concept

The residential buildings of the Rosenstein Quarter were constructed to Efficiency House 55 standard (EnEV 2014) in accordance with the funding guidelines of the KfW Bank. They are designed for a primary energy demand of between 27.4 and 31.5 kWh/m2 of heated area per year. To achieve these values, the client and energy planners opted for a forward-looking heating, cooling and electricity concept with perfectly matched components from Viessmann; a concept that was able to combine a favourable energy balance with reduced use of fossil fuels and minimal CO2 emissions.  

In this modern residential quarter, the principle of sector coupling is pursued: in addition to an ice energy store as the primary energy source for heating and cooling, a large heat pump, a gas condensing boiler, a combined heat and power (CHP) unit and a photovoltaic system supply the building complex with heating, cooling and electricity. Urban living without owning a car is altogether possible here, with residents using a car-sharing scheme with electric vehicles. The electricity needed to charge the electric cars is generated by the CHP unit and photovoltaic modules directly in the residential complex itself.

Highly efficient interaction of all components

The heating centre is located in the basement of the residential complex, with a Vitobloc EM 50/81 CHP unit at its core. The CHP unit works according to the principle of cogeneration: a long-life, natural gas-powered engine generates heat and power in a coupled process. This involves converting mechanical energy into electricity to be used as the drive energy for the Vitocal 350-G heat pump for heating and cooling. The thermal energy, on the other hand, is absorbed via a Vitotrans 200 heat exchanger coupled to the CHP unit and is used for space heating or DHW heating.

During peak loads, such as on cold winter days, the system is supported by a modern Vitocrossal 300 gas condensing boiler with an output of 605 kW. The perfect interaction of all components makes it possible for the required heating energy and some of the electrical energy to be obtained directly from within the residential complex itself. This reduces both energy costs and dependency on public power supply utilities.

Innovative ice energy store system

An ice energy store with Viessmann technology was installed in the ground at the southern end of the site of the first construction phase for the residential complex. The concrete block, measuring approx. 17 metres long, 9 metres wide and 6 metres deep, is filled with around 800  m³ of water and serves as a long term energy store for the heat pump: during the heating season, the pump extracts energy from the ice store until the water inside is mostly frozen. It utilises the crystallisation energy that is released when water freezes into ice. This process provides the same amount of energy that is needed to heat one litre of water from 0 °C to 80 °C. The energy generated in this way is fed into the underfloor heating of the residential buildings during the heating season.

In regeneration mode, the ice is thawed again. This change of physical state can be repeated as often as required and the technology is virtually maintenance-free. At the end of the heating season, ice is selectively formed which is then available as a cooling source for keeping the building cool on hot days. In summer, the lower outdoor temperatures at night can be used to cool the water in the store or the building itself via solar air absorbers.

Viessmann ice energy store systems do not require a permit and can even be used in water protection areas. The use of crystallisation energy and the combination of three energy sources –– ambient air, solar radiation and the ground –– are a guarantee of high efficiency.

Intelligent energy source management

Intelligent energy source management ensures the reliable, efficient interaction of ice energy store, solar air absorbers and heat pump. This means that all relevant system data is continuously evaluated. The results form the basis of a reporting system that is created by a team of experts and passed on to the operator. The performance figures of the heat pump can be optimised by taking individual requirements into account, for example. The outcome is the lowest possible consumption of electrical energy and a correspondingly attractive seasonal performance factor.

By putting the recommended actions into practice, the system's potential can be fully exploited, allowing savings to be made on running costs.

Free solar energy through solar thermal systems and photovoltaics

The solar air absorbers are installed on the flat roofs of four of the seven buildings from the first construction phase. In the summer, the system, which measures 351 square metres, feeds the solar energy it obtains into the frozen ice store to defrost it, so that it is regenerated ready for the heating season. Regeneration always takes place when the absorber is warmer than the ice store, so it is possible even on a mild winter's day.

The solar air absorbers are open, unglazed collectors. They utilise heat from the ambient air as well as sunlight for regenerating the ice store, and as a direct heat source for the heat pump. Unglazed solar air absorbers are especially suitable for the ice energy store system because they provide it with energy even when the air temperature is low and there is no solar radiation. The absorbers use free environmental energy continuously –– both from the ambient air at night as well as from solar radiation in the daytime.

Two further flat roof areas are used to generate electrical energy with the help of a 408 square metre photovoltaic system. Using solar energy in this way can save around 260 tonnes of CO2 per year. This is the equivalent of driving two million kilometres by car in a year.

The photovoltaic system also supplies electricity for the building's ventilation system, lifts and lighting, as well as the electric car pool.  

Innovative mobility concept

After housing, mobility is another basic human need. This is why Siedlungswerk has developed an individual mobility concept for the new residential quarter as part of the "LivingLab BWe mobil" Electric Mobility Showcase research partnership of the Federal Republic of Germany.

The availability of an electric vehicle sharing scheme directly at the place of residence opens up new mobility options and is an environmentally responsible alternative to owning a car. The electricity generated in the residential complex is first stored in the battery system and then supplied to household consumers as needed, or is used to charge the electric vehicles. This has a positive effect on both the energy balance and CO2 emissions. After all, electric vehicles not only reduce noise levels, they also lower pollutant emissions.  

The innovative mobility concept as an essential component of urban living has met with a consistently positive response and attracted attention across Germany. This has made it possible to create new collaborative arrangements and demonstrate how electromobility can be a meaningful component of an efficient overall energy concept.