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The north side of the renovated school building: The two school wings and the intermediate building frame the northern schoolyard. The five ventilation systems are situated on the roofs.
© BTU Cottbus-Senftenberg
Refurbishment to Passiv House School
Projektinfo 08/2017

Floor plan of Max Steenbeck Secondary School.
© ARGE Steenbeck, Cottbus

School wing B before the renovation: The thermographic image shows the insufficient thermal insulation on the facade.
© GWJ Ingenieurgesellschaft für Bauphysik

Summary: Built-in building services technology
© BINE Informationsdienst
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School: Refurbished from Plattenbau to Passive House

The school building belonging to Max Steenbeck Secondary School in Cottbus was old and the extent of the building damage made it impossible to carry out renovation work during the school's ongoing operation. This meant that the school had to move. To this end, an old system-built “Plattenbau” school with an auditorium and gymnasium had to be first of all comprehensively modernised. The City of Cottbus placed high demands in terms of the energy consumption, comfort and operating costs. After two years of construction, pupils and teachers moved into the renovated building in October 2012. The users praise the very attractive appearance and the pleasant indoor environment.

The old double-wing school building was built in 1974 with precast concrete panels using the “Lightweight Multi-storey Construction-Cottbus” (LGBW-Cottbus) Plattenbau building system. This building type deploying a reinforced concrete frame and wall panel structure was once widely used in the region. Five identical schools can be found in Cottbus alone. This enables the experience gained from this building project to be used for further projects.

The city first of all investigated four possible renovation alternatives in a feasibility study: demolition and new construction, renovation according to the German Energy Savings Ordinance (EnEV), renovation according to the Passive House standard or renovation to become a net energy plus building. Despite higher construction costs compared with standard refurbishment according to EnEV, the study showed that the most economical measure would be modernisation according to the Passive House standard. Taking into account a period of use until 2045, the lower operating costs balance out the higher construction costs. For this reason, the City of Cottbus chose this variant.

The construction measures started in 2010 once the planning phase had been completed. The old building was completely gutted and then renovated according to Passive House criteria. The facade was clad with 30-cm-thick thermal insulation and the windows were furnished with triple glazing. The average U-value of the building envelope is 0.28 W/m2 K.The building also impresses with its excellent air-tightness of n50= 0.32 h–1, a prerequisite for efficient ventilation with heat recovery. A geothermal array warms the supply air for the ventilation system in winter. The school is warmed by district heating produced from cogeneration. In addition, a solar thermal system supports the domestic hot water supply for the sanitary rooms in the gymnasium. The science-oriented, all-day secondary school with a canteen is attended by about 500 students.

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Timetable regulates the ventilation times

Five central ventilation units with a heat recovery system, which are housed on the roof of the school, supply the building with fresh air. An airflow rate of 20 m3/person ensures the basic air change, which is designed for 45-minute lessons. For longer teaching sessions, which are 90 minutes long at Max Steenbeck Secondary School, it may be necessary to briefly open the windows during the lesson. A greater mechanical air exchange is not recommended, as there is not much space for ducts and systems in the renovated property. In addition, this could lead to flow noises, draught phenomena, dry air in winter and greater power consumption.

In rooms without significant pollutant sources, the CO2 content of the indoor air is the standard indicator of the indoor air quality. In other building projects, sensors detect the carbon dioxide concentration and control the ventilation system using the building control system (BCS). Experience has shown, however, that the sensors are susceptible to faults and can give faulty signals to the BCS. As a result, the designers decided to use the timetable as a control element in order to ventilate only the rooms that are used. This saves energy and the ventilation capacity, but makes it necessary to integrate the timetable into the BCS. In the beginning there were problems with the software systems. In the event of unscheduled occupancy, the ventilation can be activated via presence detection buttons in the rooms. Depending on the internal and external temperatures, the supply air is pre-heated or pre-cooled using borehole heat exchangers.

Borehole heat exchangers regulate the temperature of the supply air

24 borehole heat exchangers provide the heat to regulate the supply air for House A, the intermediate building and the auditorium, and to keep the ventilation systems free of ice in winter. The results of the monitoring confirm that the system has been correctly configured. Even after several hours of operation, the temperature of the brine pumped from the ground does not drop below 7 °C in winter and does not rise above 16 °C in summer. The geothermal heat exchangers thus supply 10 % of the heating and cool the supply air in summer. This corresponds to an average of 17 MWh of heating and 16 MWh of cooling energy. On average, the temperature of the supply air is 10 K below the outside temperature on days in midsummer. However, the effect on the classrooms is low since the massive walls and ceilings store much of the heat and the air exchange rate cannot be significantly increased. This results in a temperature drop of 0.5 K compared with rooms that are supplied with uncooled air. Although the total cooling capacity of the supply air does not reach the classrooms, the cooling of the ducts benefits the entire building.

Projektinfo 08/2017:
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Stadtverwaltung Cottbus

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BTU Cottbus

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IREES
Institute for Resource Efficiency and Energy Strategies

Info tip

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BINE-Themeninfo I/2015