Practices

Plus-energy Willibald-Gluck-Highschool in Neumarkt i.d.Opf, Germany

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Building Summary
Location Woffenbacher Str. 33, 92318 Neumarkt
Building Owner Landkreis Neumarkt
Architect Berschneider + Berschneider GmbH
Coordination Berschneider + Berschneider GmbH (ARGE NB WGG)
HVAC planer EGS-plan (LPH 1-4); IB Hauer & Partner (LPH 5-8)
Monitoring Technische Universität Braunschweig, Institut für Gebäude- und Solartechnik
Type of school High school
No. of classrooms 65
No. of pupils 1,400
Gross floor area 16.256 m2 (School), 3.479 m2 (Gym)
Net floor area 12.732 m2 (School), 2.855 m2 (Gym)

 

 

Architecture

 

The Willibald-Gluck-high school including a three field sports hall is located on the western edge of Neumarkt and is surrounded by relatively large green areas. The access route of the campus runs from east to west. It leads from the western car park to the main entrance, along the gym in the direction of the canteen, which is located at the former location of the high school. The façade design of the high school is based on the prominent red precast concrete facades in the upper floors, whose visible joints characterise the appearance of the long-drawn structural body. The windows of the upper storeys with the coloured glass panes in front of the opening wings break up the outward appearance of the façade. The ground floor is provided with a continuous glass facade.

 

A large protruding block on the first floor, in which offices are housed, marks the main entrance to the school and at the same time serves as its canopy. The four-storey school has two inside atriums (see Picture 4), which serve as a recreation halls.

 

Thermal Envelope

 

The school building and the gym are built in solid construction with a red coloured concrete facade. On the ground floor, the facade is built as a mullion and transom construction. The external walls of the upper floors of the school building as well as the external walls of the gym are built as a sandwich construction, with an insulation layer of 16 cm polyurethane hard foam insulation with a thermal conductivity of 0.024 W/mK between the load-bearing construction of reinforced concrete and the red-coloured concrete reinforcement shell.

 

During the construction phase great efforts have been made to ensure an air-tight building envelope. An air change rate at 50 Pa pressure difference during the blower door test of ≤ 0.6 l / h was defined as the planning goal. After completion of the blower door test, the n50 value was 0.18 h-1 for the school building and 0.47 h-1 for the gym. 

 

Overview of U-values for different building components
Building component U-value [W/m2K]
External wall 0.14
Window 0.80
Atrium windows and shed windows 0.9
Mullion and transom façade 0.73
Flat roof 0.15
Floor plate 0.12/0.09 (Gym)

 

Energy system

 

A low-exergy concept was implemented for the heating and cooling of the school building and the gym. As regenerative heat sources, a 4.400 m2 agrothermal energy field with an output of 90 kWth was plowed below the nearby sports ground to supply the school building and the gym (see Picture 5).

 

As a second regenerative heat source, 96 drill piles required for the foundation were thermally activated. These are between 8 to 12 meters deep and provide a total heat dissipation of 100 kWth (see Picture 6). The cooling of the servers and building control system is used as an additional heat source. The peak load coverage as well as the DHW heating for the gym is provided by a gas condensing boiler. The classrooms are cooled by means of the activated drill piles and the agrothermal field. The cooling not only ensures pleasant classroom temperatures in the summer, but at the same time ensures the thermal regeneration of the soil. The heat transfer is carried out by a concrete core activation.

 

Picture 6:  System diagram for heating and cooling ©Fraunhofer-Institut für Bauphysik IBP

 

In order to achieve a positive energy performance over the year for the school building and the gym, PV modules were installed on the roof of both buildings. On the roof of the gym, a total of 290 PV modules with a peak output of 75.4 kW were installed on the opaque, south-oriented areas of the shed roof. 368 PV modules (95.7 kWp) with an 8° installation angle oriented towards east and 460 PV modules (119.6 kWp) with an 8° installation angle oriented towards west have been installed on the roof of the school building (see Picture 7). A Vanadium Redox Flow battery with an electrical storage capacity of 130 kWh was set up to increase the self-consumption of PV-electricity of the school and gym.

 

Ventilation

 

All classrooms are supplied by 4 central ventilation systems, which are housed in the unheated roof space of the school within the thermal envelope. They have heat exchangers with a (dry) heat recovery rate of ≥ 75%, a water-borne post-heating coil and adiabatic exhaust air humidification. The supply air is fed in on the façade opposing wall of the classrooms, and is led through overflow openings in the ceiling box into the traffic routes and into the atria, from where it is extracted by the ventilation systems (see Picture 8).

 

Picture 8: Ventilation concept of the school building ©Fraunhofer-Institut für Bauphysik IBP

 

The supply air volume flow in the classrooms is 7.4 litres per second and person with the goal that the CO2 concentration in the classroom does not rise above 1500 ppm. The supply air volume flow is controlled by means of variable volumetric flow controllers for each classroom based on the CO2 concentration. If natural ventilation is determined by the window contacts, the mechanical ventilation of the room is interrupted through the closing of the variable volume flow controller and is not continued until the windows are closed.

 

The gym is ventilated by a central ventilation system with a (dry) heat recovery rate of ≥ 75%. The mechanical ventilation is supported by natural ventilation via the shed windows. The supply air is introduced into the gym and then enters the changing rooms and shower room through overflow openings, from where the exhaust air is extracted (see Picture 9). The supply air volume is fed in as required, based on monitoring of the CO2 concentration in the gym and the changing rooms, as well as moisture in the showers and changing rooms. If the gym is used as an event hall, decentralised roof located ventilation systems with heat recovery and heating coils can be activated.

 

Picture 9: Ventilation concept of the gym ©Fraunhofer-Institut für Bauphysik IBP

 

Natural lighting

 

The natural lighting of the classrooms is ensured with high and generously dimensioned windows (see Picture 10). Through the use of an external sun shade with rotatable lamellas, the light transmittance of the glazing could be selected high with 0.75, which improves the natural light exposure of the rooms. In addition, glazing to the traffic areas and thus to the light-flooded atrium were also created in the facade-facing wall.

 

The natural light exposure of the recreation halls, the entrance area and a large part of the traffic routes (corridors and staircases) takes place via the atria with its skylights (see Picture 11). Despite their low g-value of 0.28, the sun protection glazing has a light transmittance of 0.66, which results in a very good selectivity characteristic of 2.4. The 3-field sports hall is illuminated by the north-oriented shed roof.

 

Electrical lighting

 

In the classrooms, 3 light strips are installed parallel to the facade. The classroom luminaires contain T5 lamps with dimmable, electronic ballasts. The luminaires provide a combination of direct and indirect lighting, providing a pleasant and uniform illumination of the room with reduced reflection and shadow formation. An illumination intensity sensor is installed between two light bands, which compensates the current value against the set value and, if necessary, adjusts the illumination. No presence detectors have been installed. A central OFF command was set up for switching off unnecessary lighting, which is generated several times a day via a time switch.

The lighting of the recreation halls and the entrance area is done with LED pendulum lights suspended in the atrium in order to achieve an even light distribution on the floor. The LED pendulum lights are dimmed in this case in order to meet the basic lighting requirements as a function of the daylight supply. The traffic routes are illuminated with simple light strips with T5 lamps integrated into the ceiling. The corridors are switched on and off by means of presence detectors.

 

The lighting of 3-field gym was carried out with ball-throw-proof LED luminaires with an efficiency of 140 lm/W, arranged in light bands. The luminaires were designed with dimmable DALI ballasts. The control is dependent on daylight. By means of a contact query at the dividers the whole hall, 2/3 hall or individual fields are controlled as a group.

 

Acoustics

 

Due to the concrete core activation, suspended acoustic baffles have been used in the classrooms. These have been supplemented by conventional wall-mounted absorbers and smaller areas with conventional plasterboard acoustic ceilings in order to bring the reverberation time into the optimum range for classroom use.

 

Acoustic baffles, wooden acoustic panels, acoustic blankets and acoustically effective expanded metal surfaces were used in the recreation halls to achieve a desired reverberation time of 1.4 s.

 

In the gym, horizontal and vertical gypsum plasterboard ceilings, wood fibre panels in the shed roof area, acoustic wall cladding and impact walls systems were used to reduce the reverberation time to the desired range (see Picture 13).

 

Measured performance

 

The measured final energy consumption (only for the School) delivered from the heat pump and the gas boiler amounts to 7.4 kWh/m²NFAyr., but this value does not include the energy consumption for the circulation pumps and the operation of the gas condensing boilers. The measured electricity consumption for ventilation is 5.4 kWh/m²NFAyr (see Table below). The other electrical consumes like lighting, controllers, projectors and all other electrical appliances and the circulation pumps amount to 20.2 kWh/m²NFAyr.

 

Energy demand for Final energy [kWh/m²NFAyr] Primary energy [kWh/m²NFAyr]
Heating 7.4 12.5
Ventilation 5.4 14.0
All other electrical appliances 20.2 52.5

 

The plus-energy goal of the school could not be achieved. If the electricity consumption for all consumers in the building (including user electricity) is taken into account, which corresponds to a total of 28.5 kWh/ m²NFAyr, the photovoltaic system was able to cover around 65% of the total electricity use in the current measurement year. It is still possible to expand the photovoltaic system to such an extent that the plus energy target could be achieved. However, this is not planned by the client because of cost reasons. The proportion of the produced PV electricity used by the school itself averages around 44% per year. The vanadium redox flow battery, which was installed to increase the proportion of self-use has been running according to plan since August of last year, but only achieves an efficiency level of 50% instead of the hoped-for 70%. Since the battery consumes more electricity for stand-by operation than it stores during low PV yield, it is now being considered to switch it off for testing purposes in the winter half of the year.

 

The indoor air quality was evaluated in three classrooms (see Picture 14). Room 1 is located on the first floor of the building and has a west-oriented façade. During winter (1st of January until 29th of February and 1st of November until 31st of December) the CO2-level in Room 1 exceeds 1000 ppm in 54% of the hours with room usage. During the transitional period (1st of March until 30th of April and 1st of September until 31st of October) it is 61% and during Summer (1st of May until 31st of August) 76%. For the assessment of the ventilation quality, a CO2-concentration of 1500 ppm is used as a compromise between air quality and energy consumption. The exceedance of 1500 ppm CO2-concentration in Room 1 is pretty low during winter (4%) and slightly increases during the transitional period (7%) and reaches its maximum during summer with 17% of the usage time with CO2-levels above 1500 ppm. The higher percentage of exceedance during summer, also in Room 2, can be linked to the fact that the variable volumetric flow controller of the ventilation system closes if a window has been opened, although the window wing could only be tilted and therefore is not able to provide a sufficient air flow rate. It would therefore be advisable to mount the opening sensors on the window frames in such a way that they only detect fully opened windows and only then switch off the ventilation system. If this advice is followed or the closing of the variable volumetric flow controller, due to open windows, is stopped the air quality in summer could possibly be improved.

 

Picture 14: Evaluation of the air quality in three classrooms based on the measured CO2-levels ©Fraunhofer-Institut für Bauphysik IBP

 

Picture 15: Evaluation of the room temperature in three classrooms which tends to a moderate overheating in summer and during the transitional periods ©Fraunhofer-Institut für Bauphysik IBP

 

Construction costs

 

The table below shows the construction costs of the school building and the sports hall.

 

Construction costs
Construction costs Net costs
€/m2NFA
Preparation/on-site infrastructure works 571,429 37
Buildings-Building structure 16,655,462 1,069
Buildings-Technical systems 6,521,008 418
Outdoor facilities/installations 1,747,899 112
Furnishings and artwork 260,504 17
Incidental building costs 4,025,210 258
Sum

29,773,109

1910

 

The innovative measures implemented are shown in the table below.

 

Costs for innovative building components
Innovative components Net costs
€/EB €/m2NFA
Photovoltaic system 1,376 €/kWp (291 kWp) 25.7
Vanadium-Redox-Flow-Battery 1,519 €/kWh (130 kWh) 12.7
Agrothermal field 33.4 €/m2 (4,400 m2) 9.4
Sum of all innovative components   47,8

 

Lessons learnt

• The Vanadium-Redox-Flow-Battery did not perform well enough. The losses total around 15,000 kWh within one year. • The exhaust air opening of the ventilation system for the gym caused such a high level of noise outside that the performance of the ventilation system had to be reduced during breaks. • The simultaneous operation of the thermally activated drill piles and the agrothermal field led to a lowering of the source temperature for the heat pumps, since the temperatures in the agrothermal field are clearly below the drill piles.

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Operational date

Monday, 14 September, 2015

Source of funding

Funding description

Bundesministerium für Wirtschaft und Energie (BMWi) – Funding Code 03ET1308A