The school in Olbersdorf (Saxony-Germany), Figure 1, provides an example of a successful compromise between historic conservation and energy-based refurbishment. The building was constructed in 1928 and renovation aimed at reducing its energy demand.
Figure 1: Olbersdorf school in Saxony (Germany) (Build up, 2010)
The most important starting point was to provide consistent thermal protection for the building. The building is a four-storey masonry structure with a gable roof. 180 school pupils are taught in 22 classrooms across a total usable area of around 4,900 m² (Reiss and Schade, 2010).
Large parts of the building were constructed with a solid masonry structure that had a depth of 48 cm and achieved a U-value of around 1.25 W/m²K (Build up, 2010). In order to encourage a “learning atmosphere”, the refurbishment measures also intend to improve the acoustics and air hygiene, while lowering the indoor temperatures in summer.
Figure 2: Cross-section of the Olbersdorf school (Reiss and Schade, 2010)
The key aspect of the renovation focused on facade systems, glazing and windows, daylight systems, optimised lighting, ventilation and heat recovery, active cooling, regenerative and passive cooling.
Firstly, the focus was to improve the thermal insulation of the building envelope in accordance with listed building requirements.
The thermal insulation composite system was developed using stepped profiles and adhesive technology preventing damage to the original facade and avoiding isolated or linear thermal bridges. The new energy concept reactivates existing ventilation and lighting systems.
Double windows were originally installed in the building. During the course of earlier refurbishment measures, the outer panes on the street side were replaced with double-glazed insulating glass and the inner panes of the double windows were removed.
Figure 3: Old and new windows at the Olbersdorf school (EnOB, 2010)
In addition to the structural improvements, energy savings were achieved also by deploying modern heating technology and efficient ventilation strategies. Before the refurbishment, the heat was provided with a gas boiler Figure 4.
Figure 4: Gas boiler providing heating before renovation of Olbersdorf school (EnOB, 2010)
As part of the energy-based refurbishment, a ground-coupled gas absorption heat pump was installed, with peak load compensation provided by the gas boiler. The use of the ground as an energy source for the heat pump system was provided as part of a comprehensive redesign of the open spaces to the east of the main building.
Before renovation, ventilation was provided via the windows and exhaust air ducts integrated into the masonry structure. However, these exhaust air ducts were only full functioning in the entrance areas and partly in the toilets, whereas in the classrooms they had been mostly blocked off during previous renovation work.
In the sanitary spaces, a conventional central exhaust air system was installed during renovation with a presence control. For the teaching spaces, customised ventilation was developed, substantially based on natural uplift and only boosted with fans with low electrical consumption as appropriate (“hybrid ventilation”) as presented in Figure 5.
Figure 5: Ventilation scheme after the renovation of Olbersdorf school (EnOB, 2010)
The replaced windows were built with thermal insulation glazing installed in double air-supply windows. Via an opening in the lower frame, the external air enters the cavity between the panes, warms up and enters the room via the upper window frame. Because the air is pre-heated and supplied above the occupancy zone, this considerably reduces the risk of draughts. In order to prevent unwanted air currents, additional wind pressure reducers and check flaps are integrated in the windows. As soon as a specific external temperature is exceeded, the skylights in the inner panes of the windows are automatically opened, which increases the volume flow of the air change. The exhaust air ducts are also being reactivated so that used air can be removed by means of natural uplift. Should a sensor measure increased CO2 concentrations, an exhaust fan will be switched on to provide support. If the respective teaching space is not or only partly occupied, the fan remains switched off. Compared to a standard system, this considerably saves on electricity for powering the vent.
The school is naturally cooled during the summer by means of effective night cooling, which is neutral in terms of the primary energy use. By utilising the double windows and exhaust air ducts and by controlling the exhaust airflow volumes, the existing building mass can be activated and a considerable drop in room temperatures achieved in large parts of the building.
Before renovation, daylight was provided in the teaching spaces by means of windows along one side of the classrooms, on either the west or east sides. Because of the building’s position on a slope, the corridor spaces, entrance area and assembly hall received too little daylight and required artificial lighting throughout the day. During renovation, the floor plans were reworked to improve the daylight utilisation. Old light shafts were reactivated or supplemented, with louvre blinds integrated in the cavities in the double windows to provide shading, glare protection and to redirect light. In the windows on the east-southeast side, it was installed electrochromic glazing to provide solar shading that counteracts solar gain in these rooms. Any required artificial light is now controlled in accordance with the daylight and switched off centrally when the school closes at the end of the day.
The refurbishment of the school aimed at reducing the heating requirement by more than 80%. Insulation measures adopted and results in terms of levels of insulation achieved are reported in Table 1.
Table 1: Technical characteristics of the thermal envelope of the Olbersdorf school before and after renovation (BMWi, 2010)
|
Component |
U-values [W/m2k] |
Description |
|
|
Before renovation |
After renovation |
||
|
External wall |
1.25 |
0.34 |
7cm ESP insulation |
|
West facing windows |
1.70 |
0.90 |
Double air-supply windows |
|
East facing windows |
2.80 |
||
|
Top floor ceiling |
1.70 |
0.22 |
- |
|
Floor |
3.50 |
0.36 |
10 cm concrete |
|
3.09 |
0.32 |
10 cm concrete |
|
Energy consumption was reduced drastically after renovation as it is reported in Figure 6 and Table 2. The overall investment cost was 8.8 million € which means 1570€/m2.
Figure 6: Energy savings in Olbersdorf school (EnOB, 2010)
Table 2: Energy efficiency improvement in Olbersdorf school before and after renovation (EnOB, 2010)
|
|
Before refurbishment |
After refurbishment |
|
Heating energy demand [kWh/m2yr] |
122.7 |
31.8 |
|
Overall primary energy requirement [kWh/m2yr] |
174.2 |
48.9 |