Umweltbundesamt Dessau, Dessau | Germany

The new building for the  Ministry of the Environment combines a compact volume  and a high degree of thermal insulation with strategies of intelligent engineering and utilises renewable energies. In particular it will benefit from the use of one of the largest thermal heat-exchangers currently available.

Ventilation

Energy consumption is further limited by maximising natural ventilation. Every office is approximately 5 m deep and has a large tilt-and-turn opening window to the external façade or the atrium. To avoid overheating in the summer, retractable horizontal blinds sandwiched within the triple-glazed window, provide adjustable solar shading. In the atrium, similarly, mechanically operated roller blinds provide additional shading to the glazed roof. In addition to the natural ventilation system, the building has an energy efficient mechanical ventilation system. Supply air is drawn through an underground geothermal heat exchanger by four air-handling units in the basement. The heat exchangers are used throughout summer and winter. Over 5 km of subterranean ducts provide an annual output of 86,000 kWh of heating energy in the winter and 125,000 kWh of cooling energy in the summer. The network of underground pipes includes 1,500 mm diameter concrete header ducts and smaller 300 mm diameter metal cross ducts. The five air intakes are sculptures made out of folded steel, located around the external perimeter. 138,000 m³/h (38.33 m³/s) of air is introduced through the four air-handling units, via riser shafts located beside the staircase cores into the offices and the base of the atrium. The exterior and interior offices are independently controlled. From the riser, air is mechanically ducted and supplied to each office via a narrow linear slot diffuser located in a bulkhead above the door. Air is exhausted from to the corridor via special sound-absorbing slots located in panels beside the doors. The corridors act as a return air plenum.
In the winter, air is extracted directly from the corridors into the exhaust air duct at five places on every floor next to the main risers, where it is passed through a heat exchanger before being expelled. In the summer, the exhaust air travels directly into the atrium through natural convection. Heat recovery is fitted to all air handling units. Apart from specialist areas, there is no mechanical cooling. Instead, the heavy thermal mass of the building has been used, with ventilation, to cool the structure at night. This is achieved by large mechanically operated opening vents in the glazed atrium roof, in combination with mechanically operated openings adjacent to, and independent from, each external window. These openings allow night air to enter the perimeter rooms via external louvres – secure and protected from the rain. The atrium also has additional vents at ground floor level which can be used in high temperatures to flush through this space.

Sunlight provides cooling

A solar air conditioning system provides cooling for the conference room and the kitchen’s walk-in freezers. 354 sqm of solar vacuum tube heat collectors at roof level provide a peak thermal output of 242 kW. These feed a 69 kW cooling capacity adsorption chiller, which uses silica gel. Additional heat for the chiller is supplied from a district heating system.

The energy source for the district heating plant (Stadtwerke Dessau) is a local landfill gas site, which provides 906 kW to the building. The heat is used in the ventilation plant for background heating, hot water and to drive the adsorption chiller. The solar water panels supplement the heating system. Each office has its own individually controlled radiator designed to achieve a room temperature of 22.8C. Additional renewables have been provided in the form of photovoltaic cells integrated into the atrium glazed roof: 228 sqm of cells achieve a peak electrical output of 31.3 kW and an annual output of 24,000 kWh.

Energy consumption for the lighting has been minimised partly by optimising the use of daylighting and partly by using a lighting control system. The relatively narrow width of the office floor plate (11.8 m) ensures good daylight penetration. In addition, the proportion of window glazing has been optimised throughout 35% of the exterior and 60% of the interior façades to maximise daylight without too much solar gain. Finally, internal surfaces direct and reflect daylight. Lighting control to individual offices is achieved by an occupancy control system.

Images 1-2: © Jan Bitter | Images: © ZWP Ingenieur-AG