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Stuttgart-Sonnenberg: Reduction of CO2 Emissions in a Nursing Home

Istaknut Je Slučaj 2009 Highlighted Case
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A retirement apartment building built in Stuttgart-Sonnenberg in 1965 is a good example of what can be achieved when a major renovation is combined with an energy efficient retrofit concept developed by a holistic design team. The modernisation of the building services by including bathrooms in the residents' rooms meant altering parts of the building's structure. Coupling these modernisation measures with energy efficient retrofit measures meant that the occupant comfort could be increased while dramatically reducing the energy costs. The primary energy use of the building could be reduced from 522 kWh/m²a to 180 kWh/m²a, which means by about two thirds, through high performance insulation of the building envelope, a combined heat and power unit plus a gas condensing boiler for peak load.

The seven story main building of the retirement home was built in 1965 with originally 116 beds. It also incorporates a kindergarten. In 1974 a further building was added as a nursing home with 55 beds. To this second building no renovations were carried out. Parallel to the renovation of the original main building new offices, a dining room and an entrance foyer on the ground floor were added. Due to originally being built as retirement apartments the main building had only limited usage as a nursing home. A disadvantage of the layout of the main building was that the rooms were separated by long corridors into three zones and a small somewhat dark common room squeezed in between elevators and the stairwell.

The east and west facades were constructed using an insulated light wooden wall with a U-value of 0.66 W/m²K. The north and south facades were constructed from a layer of hollow clay bricks and concrete. The U-value being 1.4 W/m²K. The windows were double glazing in wooden framing. On the roof of the 6th story there are several mobile telephone antennas with switchboxes installed that were not thermally separated from the concrete roof. The connections for the steel fittings were simply driven through the roof insulation. Another thermal bridge was the concrete supports for the balconies. The paint on the east and west facade’s wooden paneling had peeled of in many places due to weathering. Corrosion problems were visible in the concrete construction of the balconies. In the building were no moisture and mildew problems evident. This was due to high room temperatures and long window opening times in the winter.

The heat supply was through two gas boilers with a combined capacity of 1862 kW and an efficiency of 84%. Both gas boilers were controlled by a switch box with components installed in 1965. However the system was manually switched and controlled by the caretaker. The pressure was maintained using two regular membrane pressure drums. The heating was distributed to the following groups - Domestic hot water, Tower east with Kindergarten, Tower west with Kindergarten, Nursing home (1974), Ventilation 6th storey, Ventilation kitchen and corridors. The kitchen and dining room have a modern 2-level supply and exhaust ventilation system with heat recovery installed in 1997. For the inner lying corridors in the tower there was an air supply ventilation system connected to the heat supply. However it was not in use but the heating circulation was left on to protect against frost. For the inner lying WCs and bathrooms (also for those apartments that had) are two central ventilation systems. Apart from the kitchen all other ventilation systems were in a poor state. The lighting also was not state of art. In corridors, offices, and common areas were long florescent lights with normal switches. There was no automatic regulating of the time switched on. In the apartments there were regular light bulbs in lamps mostly bought by the occupants themselves. In the cafeteria, dining room, foyer and gallery rooms the light bulbs have been replaced with compact florescent lights in the 90’s.

The retrofit concept was developed by analysing various energy saving measures and combining them to a cost-potential curve in order to find the most profitable ones to be realised.

Features of the retrofit

1) Balconies incorporated into the apartments

2) Highly insulated walls and 3-pane low-E coated windows

3) Solar air collectors

4) Improved insulation of the roof

5) New heat generating system

6) Daylight controlled lighting system

On the east and west facades the balconies were incorporated into the living space which meant a new facade. A light wooden construction was able to be used with 20 cm mineral wool insulation. To ensure enough daylight for the often bed ridden occupants and the common rooms 2/3 of exterior wall area is transparent and 1/3 opaque. In total 50 m² of air collectors are also incorporated into both facades. All windows were replaced. The U-value of the new windows is 0.8 W/m²K. The north and south facades were insulated with 20 cm polystyrene. The roof was insulated with 22 cm polyurethane with lambda=0.3 W/(mK). The cellar ceiling and walls between heated and unheated rooms were insulated. Due to ceilings with or without installation piping insulation thickness and material varied.

The heating system was completely rebuilt. A combined heat and power station with a heating output of 100 kW and 50 kW electric power output is the heart of the system. A condensing gas boiler (310 kW) was installed to cover the rest of the requirements. A second low temperature gas boiler (310 kW) was installed to cover particularly high demand periods. For the two main heat sources there are also installed exhaust gas heat exchangers. There is a central distribution system with six separate circulation systems. Included are DHW, tower east, tower west, the later built nursing home, kitchen with dining room and the new foyer with offices. In the east and west tower there are 10 separate circuits for supplying the heat to the separate rooms over one another. The radiators in the apartments were connected to window status sensors (sudden temperature drops) so that when the windows were opened for a short time the heating switched of.

The supply air is secured either through slits built into the windows or in some rooms over an air collector beside the window. The exhaust air from bathrooms and WCs that lie on top of each other are connected and result in a total 9 separate exhaust systems. Normally 15 m³/h air is exhausted but it is increased to 30 m³/h when the bathroom is in use. During the renovation all lighting systems were renewed with low energy lights. All the lights in the occupant’s room are manually switched. In corridors and common rooms are a mixture of permanently on security lights, lights manually switched and lights connected to a light detector. In the common rooms on the west side over the normal windows were also windows with light redirection glazing installed so even when the blinds are down daylight comes into the room without glare effects. In the apartments an air exhaust is installed.

The heating energy demand of the building before the retrofit accumulated to 191 kWh/m²a whereas the first three heating periods after the renovation were measured to 56.2 kWh/m²a, 54.4 kWh/m²a and 40.9 kWh/m²a. The electric power consumption for lighting in the occupants rooms was approximately 3.0 kWh/m²a. Due to the daylighting sensors in the corridors, in the second and third measurement periods there was a saving of 4.3 kWh/m²a and 2.4 kWh/m²a electric power respectively. However in the common rooms no savings could be determined. The total electricity consumption in the renovated tower, new extension and kitchen combined was on average 60 kWh/m²a. Power for the pumps and fans lay by 4 kWh/m²a. Electric power generated by the power station was in average over the three periods 51.8 kWh/m²a.

The primary energy consumption after the retrofit is with 185 kWh/m²a 65 % less than before the retrofit (522 kWh/m²a) and therewith significantly better than the original saving target of 50 %.

Acronym of the case

Nursing Home Stuttgart Sonnenberg

Author(s) information


Heike Erhorn-Kluttig


Fraunhofer Institute for Building Physics



Johann Reiss, Michael Beckert


Fraunhofer Institute for Building Physics


Lessons learnt

Despite a higher inner surface temperature through better insulation and exhaust air over the bathrooms the set room temperature was difficult to maintain due to long periods of open windows in most rooms. This meant that the separate room control system was not very effective. The well day lighted west orientated common rooms were a positive and are used often by the occupants. The setting of the room temperatures on the central control unit in the nurses’ room is not self-explanatory. It took a while despite manuals and demonstrations before the care givers were able to operate them. The lighting that was controlled by a light sensor showed in some areas that significant saving in electricity could be achieved despite some lights being on day and night for safety reasons. The integration of the balconies in the living space and the inclusion of bathrooms also proved to be a plus with the occupants not even missing the balconies. Rooms with a continuous fresh air supply over the air collectors had a much better air quality than those rooms with only passive ventilation in slits over the windows and the air exhaust fans in the bathroom. Planned transparent insulation could not be incorporated on the south facade as the product was removed from the market at that time. However the conventional insulation proved much cheaper and planning wise easier to incorporate. The heavy triple paned glass windows a problem for the occupants to open and close properly and they not helped by the high positioning of the handles. The total primary energy usage was reduced by nearly two thirds.

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Start date - End date

nedjelja, 1 July, 2001 to utorak, 30 September, 2003

Operational date

srijeda, 1 October, 2003


In total 30 of the occupants and 15 of the care givers took part in a user evaluation. A third of the occupants lived in the house before the renovation took place. 83% of the occupants found the room temperature in winter comfortable but only 43% in summer. 83% of the occupants were also happy that the room temperature was automatically controlled with each room able to be separately controlled. Most of the occupants are happy with the air quality but feel it is necessary to ventilate over the window. CO2 measurements in the rooms confirmed this. 87% of the occupants find it an advantage to have the bathroom in the apartments and the sound from the fan was not noticeable. General points from some of the occupants were that the rooms are too small for wheelchair users and the window handles are too high, also generally the windows are difficult to open and properly close.

Relevant tools



Görres, J., Erhorn-Kluttig, H., Reiß, J., de Boer, J., Erhorn, H., König, A., Kühnle, P.: Erarbeitung und Realisierung eines modellhaften Sanierungskonzepts für ein Alten- und Pflegeheim in Stuttgart-Sonnenberg. Abschlussbericht. Landeshauptstadt Stuttgart, Amt für Umweltschutz (2008).
Görres, J., Klenk U., Erhorn, H., Kluttig, H. und König, A.: Sanierung des Altenpflegeheims Stuttgart-Sonnenberg aus energetischer und architektonischer Sicht. Gesundheitsingenieur, 3 (2004), S. 134-141.

Source of funding

Funding description

The retrofit of the nursing home Stuttgart Sonnenberg received co-funding by the national German programme EnSan (energy efficient retrofit of buildings). EnSan is a programme by the Federal Ministry of Economy and Technology (BMWi) and is managed by Projektträger Jülich (PTJ).

Economic effect

The investment costs for the energy related measures at the building envelope amounted to 2.7 Mio Euros, the costs for the building service system replacement to 1.3 Mio Euros with planning costs of about 900000 Euros.