Practices

Plus-energy St. Franziskus Elementary School in Halle, Germany

Highlighted Case March 2017
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In Halle (Saale), a plus-energy school was built as a sustainable and ecological construction made with a timber frame and cellulose insulation in accordance with the Passive House standard. The building replaces the old existing site of the St. Franziskus-Elementary School in the surrounding area. The new school is a three-storey building with two interconnected structures: the after-school care and class area (west structure), as well as the administrative wing with the school canteen and caretaker's apartment (east structure).

 

The building envelope has very high thermal protection as a result of the cellulose insulation. Apart from the timber frame, there are only two staircases elements made of reinforced concrete and an innovative window system. This innovative system consists of two double-glazed windows integrated into a singular frame in order to reduce the thermal bridge. These double glazed insulating glass windows contain blinds in between and therefore ensures a low heat requirement, which is further reduced by means of the ventilation system with heat recovery. The school building covers a large part of its electricity needs with two photovoltaic systems installed on the school's roof and on the carport.

 

The school building was put into operation in February 2014 and its energy consumption has been monitored since then.

 

 

Location

 

Murmansker Street 13, 06130 Halle (Saale), Saxony-Anhalt, Germany

 

 

Project team

 

Project management: Hollenbach Sachverständigenbüro

Architect design: Steinblock Architeckten GmbH

Structural engineering: Theurich + Klose GmbH

Electrical system: AIB GmbH – Architekten Ingenieure Bautzen

HVAC system: IB Naumann und Stahr

Consultant and Monitoring: Hochschule Magdeburg-Stendal (University of Magdeburg-Stendal)

Other collaborators: GEDES eV / IB Kriegenburg / APW Heizung und Sanitärbau GmbH / SET Solar Energie Technik GmbH / HM Heizkörper GmbH & Co. KG

Support: European Regional Development Fund (ERDF) / Federal Ministry of Economic Affairs and Energy (BMWi) – Program EnEff:Schule / Land Sachsen-Anhalt (Federal state of Saxony-Anhalt) / Stadt Halle (City hall of Halle)

Owner: Edith-Stein-Schulstiftung des Bistums Magdeburg

 

 

Time schedule

 

Design: 2008 -2011

Construction: 2012 - 2014

Completion date: January 2014

Official inauguration: February 2014

 

 

Building use and area

 

The new St. Franziskus Elementary School consists of a primary school and kindergarten with 20 classrooms for approximately 200 pupils in total. On the ground floor, there are technology and lavatory facilities, a school kitchen, an auditorium in the east area and a nursery on the west side. The first floor is comprised of classrooms and the administration offices. The hall is on two storeys. The caretaker´s apartment is located In the eastern area of the second floor, and further classrooms and lavatory facilities in the west wing. Transparent classroom walls in the hallways create an open learning atmosphere which allows for a generous sense of space.

 

Total Constructed Floor Area: 3,770 m2

Total Usable Floor Area: 3,132 m2 (according to EnEV, the Germany's Energy Saving Ordinance, is 2,019 m2)

Total Conditioned Area (EBF – Energiebezugsfläche): 2,965 m2

 

 

Construction costs

 

Total: 6,906,192 €

Preparation / on-site infrastructure works: 180,962 €

Buildings – Building structures: 3,425,089 €

Buildings – Technical systems: 1,139,899 €

Outdoor facilities / installations: 549,289 €

Furnishing and artwork: 399,112 €

Incidental Building Costs: 1,240,732 €

 

 

Envelope performance

 

In order to achieve the desired passive house standard, the building envelope was constructed to be highly insulated and as free of thermal bridges as possible. In addition to this, the wish of the builders for sustainable and ecological solutions in the construction were also necessary. With these requirements for the building envelope, the planners opted for a timber frame construction, which is made up of 80% renewable material.

 

The structure of the outer wall is made from double T-timber beams. The panels are fixed to the inside of the belt. The exposed spaces are filled completely with cellulose insulation. In doing so, the straps of the beams are also insulated in order to minimize the heat bridges of the column structure. The gypsum fibre boards facing the interior are attached to horizontal battens and are decoupled in order to reduce sound transmission. The rear-ventilated outer panel consists of cement panels or thermo-wood.

 

The natural lighting is mainly via the window surfaces arranged in the perforated facade. In order to optimize daylight incidence, the external window sills of the box window frames were executed with reflective surfaces. The shading and darkening is carried out with automated slats, which are mounted independantly between the inner and outer window. With this arrangement, the shading system is protected against weather influences. The slats have two different surfaces which are used according to season, either a reflective surface for the warmer months or an absorbing surface for the cooler weather. In the warmer months, the metal-reflecting surface reduces the heat input for the interior. To generate the solar gains in winter, the black surface is positioned outwards to absorb the heat.

 

In order to improve the acoustics of the room and the intelligibility of speech, acoustic panels were used in the classrooms in the central area of the ceiling. Acoustic plasterboard perforated ceilings were installed to reduce the reverberation time in the hallways.

 

An overview of U-values for different building components is shown below:

External wall: 0.11 W/m2.K
Solar thermal wall: 0.16 W/m2.K
Windows: 0.60 W/m2.K
Mullion and transom façade: 0.60 W/m2.K
Flat roof: 0.10 W/m2.K
Floor plate: 0.13 W/m2.K

 

The air tightness of the building envelope is measured with an n50 value of 0.24 h-1. Three years after the first measurement, a second one was performed confirming the air tightness with a measurement of 0.246 h-1.

 

 

Energy consumption

 

The measured final energy consumption (only for the school and the nursery) delivered from the district heating amounts to 12 kWh/m2.y and the measured electricity consumption for ventilation is 13.8 kWh/m2.y. The other electrical consumption such as lighting, controllers, projectors and all other electrical appliances, amounts to 12.7 kWh/m2.y.

 

The plus-energy goal of the school is based on the primary energy consumption and the production of primary energy. The consumption taken into account is heating, cooling, DHW, lighting and ventilation. Unfortunately the consumption for lighting is not measured separately. Therefore the whole energy consumption of the building has to be compared with the primary energy production. The primary energy consumption for the whole building amounts to 72.2 kWh/m2.y while the production amounts to 77.8 kWh/m2.y. As a result, the measurement shows that the plus-energy goal is achieved.

 

According to the Usable Floor Area, a summary of results is listed below:

  • Total primary energy consumption 72.2 kWh/m2.y. Breakdown in kWh/m2.y.: Heating: 3.3; Ventilation: 35.9; All other electrical appliances: 33.0.
  • Total final energy consumption 38.5 kWh/m2.y. Breakdown in kWh/m2.y.: Heating: 12; Ventilation: 13.8; All other electrical appliances: 12.7.
  • Total primary energy renewable production: 77.8 kWh/m2.

The indoor air quality in two classrooms has been measured and the CO2-level during classroom usage (measured via movement detectors) is in 27% of the hours with a usage above 1000 ppm and only 0.4% above 1500 ppm considered over a whole year, therefore providing very good indoor air quality for the pupils.

 

The evaluation of the room air temperature is based on the comfort band from chapter NA.3.2 of DIN EN 15215: 2012-12 [DIN V 15251], which is valid only for rooms in which the users can adapt their clothing. This is the case for schools in the usual clothing resistance between 0.3 clo and 1.0 clo. Looking at the two evaluated rooms the room air temperature exceeds the comfort band in 26% of the usage hours over the course of a year and falls below in 3% of the time. The problem is the non-existent zone or even room regulation.

 

 

Energy systems

 

HVAC through geothermal and mechanical ventilation

 

The building is heated via the ventilation systems; no static heating surfaces have been installed. The supply air is preconditioned via the geothermal heat exchangers and then preheated by the heat recovery unit. If necessary, the supply air is further reheated. This is done via the district heating return of the neighbouring gymnasium. The supply and return temperature of the district heating for the St. Franziskus Primary School is therefore 45/35 ° C. The heated air is introduced into the classrooms and once there, compensates for the very low transmission heat losses due to the high level thermal insulation.

 

Part of the cooling is provided by natural ventilation through the box windows. During the warmer months, the avoidance of overheating is a primary focus, the surplus heat of the intermediate space can be dispensed by tilting the outer window. In winter, the solar gains are supplied to the room by opening the inner window. The mechanical ventilation concept provides for two ventilation systems in combination with heat recovery and geothermal heat utilization. Apart from ensuring the hygienic quality of the air in the rooms, the ventilation also helps the temperature control of the rooms.

 

The eastern and western parts of the building each have a central unit with heat recovery. The total volume flow for the classroom tract was dimensioned with 7.500 m³/h and the hall-tract with 10.000 m³/h. Heat transferable storage materials, so-called heat accumulators, are used as heat exchangers. They absorb heat quickly and dissipate this as quickly to the cold air stream. The constant change between outside air and exhaust air ensures high moisture recovery. The kitchen basic ventilation as well as the residential ventilation of the caretaker’s apartment are also supplied via central ventilation units with counter current channel heat exchangers (320 m³ / h supply air). The lavatory facilities have an additional exhaust ventilation system with 360 m³/h (supply air from after-flow of the room ventilation).

 

In winter, the temperature of the outside air is raised through a ground heat exchanger in order to prevent icing of the heat exchanger units in the ventilation systems. In addition, the use of the ground heat exchanger reduces the energy demand for reheating. In summer, the ground heat exchanger can be used to cool the outside air. A summer night ventilation is also provided.

 

The collection pipes (DN 900) of the ground heat exchanger are made of polyethylene, whereas the strand pipes (DN 300 and 400) are made of polypropylene. The pipes were installed in the frost-free soil with a total length of 650 m within the excavation pit. The ventilation system is temperature-controlled (exhaust air temperature, superimposed by individual room temperatures of unfavourable rooms). In addition, there are space-based presence detectors, which release the respective volume flow regulators.

 

 

DHW through solar thermal

 

The southern solar thermal wall is equipped with 36 m2 of solar thermal collectors for domestic hot water (DHW) heating for the school kitchens and the caretaker’s apartment. The solar thermal collectors feed into a 2 m³ layered storage tank with vacuum insulation (for the kitchen). Post-heating is realized by means of an integrated heating coil (with normal district heating) or by means of an integrated electric heating element for peak load cover.

 

The excess heat from the solar thermal collectors is supplied to a latent heat store (storage material sodium acetate trihydrate). The melting of the phase change material takes place at 85 °C. Due to a lack of excess heat during building operation the latent heat store is rarely used. The DHW for the school is handled with local electric water heaters (children's cafeteria, art room, meeting room, showers). The common lavatory facilities are equipped with cold water connection. The caretaker’s apartment has a 200 litres DHW-storage which is fed from the solar-thermal system and 2 local electric water heaters with an electric heating register in the ventilation system.

 

 

Electric production through PV and wind turbine

 

Two photovoltaic plants with a total output of 81 kWp, as well as a vertical wind turbine with a capacity of 1 kW, were installed to achieve a positive energy balance. The wind turbine was mainly installed for educational purposes.

 

 

Smart lighting system

 

Optimal light conditions ensure a positive learning atmosphere. For this purpose, light sensors measure the brightness in the classroom, which is composed of daylight and electrical light. This measurement is compared with the set point set by the user and is adjusted after a deviation by the electrical light input. A passive infrared sensor measures a change in the heat radiation, which is triggered by movements. If no movement is detected for a certain time, the lighting system is deactivated. Various luminaires are used depending on the space use and size. In classrooms fluorescent tubes with electronic ballasts are predominantly used. LEDs are installed for the exterior spaces. The exterior lighting is predominantly supplied via a PV-powered battery system.

 

 

Awards and recognitions

 

None

 

 

Additional information

 

Buildup news: http://www.buildup.eu/en/node/51364

Homepage of the nursery school: www.hort-sankt-franziskus.de

Homepage of the primary school: www.franziskusschule-halle.de

Project video: https://vimeo.com/163402193

Photo tour:  http://www.edith-stein-schulstiftung.de/de/schulen/geschichte/schulneubau/

Project design:

 

Lessons learnt

- There should only be common ventilation systems for rooms with the same façade orientation to be able to supply colder air to the southern oriented rooms than to northern oriented rooms. - A bypass of the ground heat exchanger would provide the possibility for more efficient mechanical night ventilation during the transitional period. - During wind lacking times (all months except November) the peripheral electrical appliances of the small vertical wind generator can consume far more than the wind generator produces - The solar system provides less excess energy than predicted, therefore the latent heat that is stored is only rarely used.

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Operational date

Wednesday, 26 February, 2014

Source of funding

Funding description

Funding was granted from the german Federal Ministry for Economic Affairs and Energy.