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4a Architecten

Photos: Christian Kandzia (4a Architekten)

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• Status:

  Realized

• Education type:

  Municipal Education
  

• Education level:

  Primary Education (pre-school + primary)
  

• Address:

  Kalbacher Höhe 15, 60311 Frankfurt am Main
  

• Client:

  Municipality of Frankfurt am Main

• Keywords:

  Low-energy building

• Programme:

  classrooms, exercise hall, dining area, kitchen, day nursery, school grounds

• Area:

  7700m²
  

• Number of classrooms:

  16
  

A passive house school as the cornerstone for urban development

Riedberg is a vast district being built on the edge of the city of Frankfurt, where a number of university departments are located. The primary school for this future residential district was designed by the municipality. A great deal still remains to be built, but the school is already in use and serves as an attraction for new residents. The school is a motor for urban development. The primary school was planned for 400 children so that it can meet the needs of the future district. This school is a solid building which complies with the passive house standard. A sports hall is also included in the project and this complies with a low energy standard. The nursery school for 125 children forms the third wing of the complex and has a separate entrance. The studies carried out for the building were intensively supervised by the Passivhaus-Institut in Darmstadt and the Hochbauamt of the city of Frankfurt.

The school consists of two stories and is built in a very compact way. The entrance to the primary school at the corner of the L-shaped building opens onto a central meeting area, which in turn opens onto the playground. The wings with classrooms have a central corridor with classrooms on either side. Good thermal insulation, airtightness, passive house windows (thermal window profiles and triple glazing) and an insulated frost fence jointly account for low heat loss. As a result, the body heat of 25 pupils and one teacher is sufficient to heat a classroom while it is used. This is an essential advantage compared to the passive house concept for houses. To achieve the passive house standard for houses it is necessary to have a good orientation to the sun, and to avoid windows in the walls facing north. For a school this is not important as it is actually the children who heat the school. In order to conserve body heat in the building, a central ventilation system with heat recovery is required. Heat exchange ensures that almost 90% of the heat is drawn from the air that is removed. This is used to heat the fresh air that is brought in. At the same time, the central ventilation provides the comfort of indoor air quality. In a traditional school building, the CO₂ level in a classroom regularly goes up to peak values. A limited heating system with two wood pellet heating units can provide extra heating during winter. The central ventilation does not stop the possibility of opening windows in the classroom. However, experience has shown that this does not even happen in summer, because many children benefit from purified indoor air, low in particles.

The solid construction of the building provides a thermal mass which can store heat. False ceilings prevent thermal exchange. On the other hand, hard concrete surfaces are disadvantageous for good acoustics. For this reason, acoustic perforated ceilings were fitted to a limited extent as a finish for the air channels. In summer this mass also provides thermal inertia. Together with the externally fitted sunblinds, this prevents overheating in summer. In the case of extreme temperatures in summer the shutters at the top of the windows automatically open at night and natural ventilation ensures that the solid concrete of the building cools down a few degrees during the night. 

The maximum use of daylight is important in order to achieve low energy consumption. Daylight penetrates into the corridors through roof lights and windows in the walls of the classrooms. The light in the classrooms must be sufficient, even at moments when the sunlight is screened to prevent overheating. For this reason the top slats of the sunblinds are attached in such a way that they always reflect the sunlight against the ceiling, even when the lower blinds are shut. The city of Frankfurt is fulfilling its pioneering role by building a second passive house school and has the ambition of achieving the passive house standard in all the new municipal buildings. The city is also convinced of the economic feasibility and has issued general directives for sustainable and economic building. In addition, it is aiming to provide photovoltaic cells on all the roofs of new buildings. The flat roofs of this school are also rented out to a supplier of green energy.