Technical building equipment diagram
© Ingenieurbüro Ebök

Energy concept: system components
© BINE-Informationsdienst
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Heating, cooling and ventilation

For heating and cooling, the building primarily uses concrete core temperature control (CCTC). Due the fact that with a thermally activated slab, the laws of physics dictate that the cooling capacity exceeds the heating capacity, the system is highly suitable for covering the established loads of this passive-house-standard office building. For the purposes of CCTC, plastic tube heat exchangers with a surface area of around 5,000 m² are laid with 10 cm clearance from the undersides of the slabs. For temperature control, 40 borehole heat exchangers protrude 100 m deep into the ground. Water flows in a closed circuit from the borehole heat exchangers, through the tube heat exchangers, and back. Thus, the ground functions as heat storage or cold storage, and the bivalent utilisation supports thermal regeneration.

In the planning phase, various temperature control options (remote cooling and remote heating alone or in combination with earth-to-air heat exchanger) were compared. The implementation of borehole heat exchangers with water flowing through them proved to be the most cost-efficient and environmentally friendly solution. Due to large-scale activation, even very slight overtemperatures or undertemperatures are sufficient to heat or to cool the energy-optimised building. One advantage of CCTC is that it also balances out temperature differences between the individual sections of the building. In winter, the building's internal yields are often enough to ensure thermal comfort. If the water for CCTC needs to be reheated, this occurs primarily via waste heat from the compression refrigeration machines for the server rooms and cold storage rooms for food. The remaining heat energy requirement is covered by remote heating. The thermal inertia of the concrete core calls for a sophisticated control concept. To charge the concrete core optimally, the required pump running time is determined upon consideration of the room temperature, slab temperature, and water temperature. The situations in which heating is required, and in which cooling is required, are separated by a neutral temperature range. Individual room control is not possible.

The CCTC is supplemented by a sophisticated ventilation concept. Outdoor air is channelled through a 28 m-long underground duct to the air supply centre, where it is further cooled (or heated, depending on the requirement) by the borehole heat exchangers. If heating is required, the heat recovered from exhaust air is used. In the event of very cold outdoor temperatures, the air can be further heated using remote heating. Spray humidification keeps the relative humidity of the supply air above 30% even in cold periods. The conditioned supply air is then channelled into the atrium. From there, it flows through noise-insulated overflow openings in the atrium facades, and through air ducts in the concrete slabs, to the exterior offices. Air quality and temperature in the atrium are monitored with measuring instruments. If required, the atrium can be ventilated naturally via smoke and heat vents; all offices and lounges have openable windows. Exhaust air is actively extracted by suction in the offices, and channelled to the central air exhaust on the roof. The concept of minimal, space-saving and cost-saving air supply and exhaust ducts entails heat recovery in the closed-circuit interconnected system. Ventilation of all office areas is controlled centrally, according to a time program. The rooms on the garden storey which are used for special purposes, such as the kitchen, cafeteria, and IT training, are directly connected to the central air ducts. In these areas, in order to take into account the significantly fluctuating load conditions, individual room control is possible by means of additional heating and cooling surfaces, as well as volume flow controllers.

Projektinfo 05/2006:
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Construction physics, BTE & simulation
ebök Planung und Entwicklung Gesellschaft mbH

Construction management