The double-winged system-built school with an assembly hall and gymnasium dates back to 1974. The redevelopment project provides a model for other schools, as this type of building is widespread throughout the region. The building was gutted and refurbished in accordance with the passive house standard. Since 2012 it has been the new home of the Max Steenbeck Secondary School in Cottbus. District heating from a cogeneration system supplies the building with heat, and efficient ventilation systems with heat recovery provide hygienic ventilation. The energy concept also includes other innovative approaches: For example, the district heat return system is used to heat part of the school and heat is stored in the ground below the gymnasium.
The Max Steenbeck Secondary School specialises in mathematics, sciences, computer science and technology. The school will move from its previous location into the new building as soon as the renovation work is completed. Located on an 18,800-m² site, the new school is situated directly next to the university campus on the north side of the city centre. The school, which is a system-built school with assembly hall, dates back to 1974. It is based on the last school system to be deployed, which utilised a combined wall and skeleton structure and was still frequently built until 1990. The use of central corridors, which is advantageous in terms of energy use, distinguishes it from the older system-built schools.
The school in Cottbus comprises a double-winged building with an assembly hall and gymnasium. The two three-storey wings, which each have basements, are linked to the assembly hall via a two-storey connection building and have 18 x 48-metre floor areas. The building is badly in need of renovation, particularly in regard to the thermal insulation, building services technology and windows. There are numerous leaks, cracks, concrete spalling and exposed reinforcement bars. The assembly hall and staircases are single-glazed. After 35 years of use, all the materials and building services equipment are fully worn out and to some extent do not work. The building is not wheelchair accessible. The building also fails to comply with fire regulations.
With the accompanying building monitoring, innovative concepts and technologies are being investigated in order to test whether they can be applied and transferred to similar types of schools (see the explanation under “Energy concept”). The use of these concepts is being analysed in regard to technical and economic aspects. The two structurally identical and symmetrical school wings enable innovative components to be installed in direct comparison with conventional versions.
The operation of the building was closely monitored for two years. To this end, the bus system was expanded and 25 heat meters, 73 electricity meters and several water meters were installed so that the energy flows and plant parameters can be recorded and stored in detail at 15-minute intervals. Web-based data retrieval was made possible to produce energy balances and to scientifically monitor building operation. During comfort monitoring, certain room parameters (e.g. indoor air temperature, radiation temperature, air current, air stratification, carbon dioxide content) are measured in different teaching units.
The renovation of the building is aimed at achieving the passive house standard, which corresponds to a maximum heating requirement of 15 kWh/m² p.a. To attain this, it is being stripped back to the structural shell and then thermally insulated with passive house components.
The verification of the passive house standard as part of the passive house project package (PHPP) has showed that the heating requirement is more than 15 kWh/m² p.a. According to the current state of planning, the passive house standard is therefore not achieved. It is therefore being examined how the thermal insulation or system technology needs to be changed in order to nevertheless reach the passive house standard. The building does, however, clearly undercut the “3-litre house” standard in accordance with DIN V 18599, which defines a primary energy requirement of 34 kWh/m² p.a. as the upper limit for the heating, ventilation and auxiliary energy.
The generous central corridor concept with two three-storey school wings is being retained while the entrances are being furnished with additional porches. The previously opened courtyard area beneath the assembly hall is being enclosed and used as the new location for the canteen and library. The corridors are being opened to the windows on the gable ends and thus expanded to form breakout areas. In front of the basement level, an external area is being created for the adjacent music and art rooms. The installation of lifts will make the building accessible for wheelchair users.
District heating from a cogeneration system supplies the building with heat while electricity-efficient ventilation systems with heat recovery ensure hygienic ventilation that is energy efficient.
In terms of the building services technology, various innovative concepts and technologies are being deployed:
- Geothermal heat storage system for utilising surplus solar heat
- Brine geothermal heat exchanger to pre-temper the supply air
- Utilisation of heat from the district heat return pipe
- Small, decentralised, high-efficiency heat pumps
The two structurally identical and symmetrical school wings enable innovative components to be installed in direct comparison with conventional versions. For example, one of the two school wings will receive district heating from the conventional supply flow (70 °C), while in some areas of the other wing the district return flow is used (50 °C). Although this requires larger heating surfaces, the efficiency of the district heating system is improved. In addition, decentralised heating pumps instead of thermostatic valves will be installed on all radiators in this school wing. These will be controlled by means of individual room regulation in accordance with the timetable and thus enable rapid heating as well as other remote control functionalities via the bus system and building control technology. In addition, this eliminates the need for hydraulic balancing with throttle valves, which can be very complicated with larger buildings, causes flow resistance and energy losses and leads to differently warm radiators on each floor.
Geothermal energy is used for the two school wings, the assembly hall, the canteen and the library. 24 brine geothermal heat exchangers every 50 metres enable passive pre-heating of the supply air in winter and cooling in summer. The ventilation with an air volume flow of approximately 20 m³/h per person is regulated using time controls and presence detectors. Ventilation heat losses are minimised by means of heat recovery.
In the area of the gymnasium, it is planned to use part of the floor slab and the ground below it to store surplus heat and low temperature heat from the solar collector. For this purpose a pipe system with three loops is being installed in existing ducts under the floor slab. This will enable surplus heat to be diverted to the ground in summer. In winter, the system will make it possible to reduce transmission heat losses from the floor of the gymnasium. This is because the floor has only been recently renewed, which is why efficient thermal insulation is not possible for economic reasons. Based on dynamic simulation calculations from a comparable project, winter ground temperatures of around 18-20 °C can be expected, which will considerably reduce heat losses via the ground.
The lighting is also being optimised. Although the lights will continue to be switched on manually, automatic switching off at the end of each lesson will prevent unnecessary lighting and the associated use of electricity.
Performance and optimisation
With a primary energy consumption of about 32 kWh/m²a for the school and 30-33 kWh/m²a for the gymnasium, the goal of a 3-litre school was achieved.
In addition to thermal insulation suitable for a passive house, and highly energy-efficient ventilation and building services equipment, the school uses innovative concepts that still had to be tested. For example, the brine geothermal heat exchangers supply about 8 per cent of the school’s heating from geothermal energy by preheating the ventilation plants. In midsummer, pre-cooling with these geothermal heat exchangers can reduce the supply air temperature for the classroom by up to 2 K. The accumulation of surplus heat from the solar collector system heats the soil beneath the floor slab of the gymnasium by about 3 K in winter. This reduces the heat consumption of the gymnasium by 6 MWh per year. By feeding back the district heating return from one part of the school to another part of the school with larger radiator surfaces, over 60 per cent of the heat requirement can be covered there with the return heat. This corresponds to savings of 16 MWh of heat.
One classroom has a heat-storing plaster ceiling (PCM). Due to high ceiling temperatures throughout the entire summer semester and insufficient nightly cooling, the storage capacity of the plaster ceiling cannot be used to its full extent.
The thermal comfort during the usage period is usually in a comfortable range, with PMV values between -0.5 and +0.5. The carbon dioxide content of the indoor air in the investigated rooms during the usage period is 98 per cent less than 1,500 ppm and is therefore acceptable. The minimum air exchange rate of the school’s five central mechanical ventilation plants of 20 m³/h and person is seen as a good compromise between the technical possibilities of renovation and energy costs. In addition, a short manual window ventilation during the breaks and in the middle of a 90-minute double lesson is recommended at full occupancy.
In order to optimise building operation, all switch-on times, target temperatures and pressures of the ventilation plants, as well as the switching criteria for heating and the use of borehole heat exchangers and solar collectors, were thoroughly checked in the first two years of operation.
By lowering the heating threshold temperature to 10 °C, the summertime activation of the heating pumps could be decreased. The heating system has been converted from external temperature control to a reference room control system in order to avoid morning heating operation in summer.
Holiday operation with its deactivation of the ventilation plants and lowering of the heating system had to be defined and programmed first. As a result, the temperature-corrected heating energy consumption in the first half of 2014 was 20 per cent lower than in 2013. It fell again by 7 per cent in the first half of 2015. Further changes related to a later activation of summer night-time ventilation only after 1.00 am, but with increased output. Manual window ventilation takes place on midsummer days between 5.00 am and 7.45 am. In principle, automatic ventilation ends at 5.30 pm. This allowed power consumption to be reduced by about 10 per cent.
Problems were also caused by the control system for the blinds. In the summer half-year, all the blinds for the building closed during the morning. In accordance with the orientation of the façades, the blinds are now only closed in an easterly direction in the morning, in a southerly direction at midday and in a westerly direction in the afternoon so as to prevent excessive energy input. Otherwise, natural daylight is used extensively. Teachers are generally able to intervene by manually operating the control systems themselves.
The renovation costs amount to 11.3 million euros. Half of this amount is being provided from funding programmes and the other half is being funded via a municipal credit scheme.
The energy costs including the base price are approx. 26 ct/kWh for electricity and approx. 15 ct/kWh for district heating. With regard to heating costs, it should be borne in mind that energy savings have only a marginal effect on costs, since the fixed base price for district heating connections accounts for more than 50 per cent of the costs. In the case of a district heating connection, the building operator does not incur any costs for the possible maintenance of the tank, storage tank and burner, as is necessary for other heat generators.
It will be possible to continue using the monitoring technology once the project has come to an end. For this purpose, the monitoring workplace will be integrated into the “UNEX student experimental laboratory”, which is available to all schools and will move into part of the ground floor. In addition to other student experiments in physics and chemistry, the building energy efficiency can be experienced experimentally, enabling the topic to be incorporated into the lessons of the scientifically oriented school as well as in events held by the BTU Cottbus. The current energy flows will also be depicted on a display panel in the school.
|Building type||System-built secondary school|
|Year of construction||1974|
|Start of refurbishment||2010|
|Measures for the school building and the gym|
|Gross floor area||10.863 m²|
|Heated net floor area||9.509 m²|
|Gross volume||40.954 m³|
|Work places and pupils||600 persons|
|A/V ratio||0,33 (before); 0,35 (after) m²/m³|
|Energy indices according to German regulation EnEV|
|Heating energy demand||26,30 (school building)||260,90 (school building)||kWh/m²a|
|Overall primary energy requirement||45,20||217,40||kWh/m²a|
|Measured energy consumption data|
|Site energy for electricity total||14,70||kWh/m²a|
|Site energy for heating and domestic hot water (dhw)||22,50||133,20 (school building)||kWh/m²a|
|Source energy for heating and domestic hot water (dhw)||93,20 (school building)||kWh/m²a|
|Total source energy||29,90 (school building); 22,60 (gym)||132,10 (school building)||kWh/m²a|
|Net construction costs (according to German DIN 276) relating to gross floor area (BGF, according to German DIN 277)|
|Construction (KG 300)||486||EUR/m²|
|Technical system (KG 400)||255||EUR/m²|
|These figures represent established costs|
|These figures represent established costs, According to Gross floor area|