BonOffice · Krefeld, D

In an industrial estate in Krefeld (Germany), an administration building with storerooms was erected within 8 months time for the company BonOffice – a service company that equips offices with coffee machines and coffee products. The company has a very distinctive understanding for the customer, which also won the “Best Service Award” 2003.

In order to meet the high demands of the new headquarters, our task was not only to take representative aspects into consideration but also to a high degree the functional and ecological requirements.

In order to avoid the usual structure for business facilities with a small office building in front and a low-priced warehouse made of gas concrete or profiled metal panels behind, the warehouse largely has been digged into earth. This structure is revetted with gridlike precast concrete units and provides the three-story office block on top of it a vegetated base. The slightly sloping terrain was of advantage to this solution. Wide stairs guide the visitor unnoticeably into the entrance level – the actual 1st upper floor.

The widely projecting roof of the entrance hall, the filigree glazing of 7 m in height, and the open-plan flooring mark off an area that obliterates the borderlines between inside and outside. The office wing has been designed as ample double-row and gets optimum illumination through large-scale glass elements in the North and South. The balconies in front of the entire Southern width provide unspectacular and efficient protection from the sun. The top floor houses the large canteen and recreation area for employees and visitors next to a terrace area and green space of 200 sqm.

Special emphasis has to be placed on the fact that the new Bonoffice administration building is operated as low-energy building exclusively by using regenerative energy. The basic saving of energy in an office building is reached primarily on cooling. Contrary to a residential building the equipment of a modern office building (computer, illumination) already serves to a large extent as heating in the winter. For the tempering of the building, the soil is used as reservoir.

The soil has as of 1.2 m depth a consistent temperature of about 14°C, which is an ideal starting temperature for an ecological tempering of a building in summer as well as winter. A small difference between flow-temperature and room temperature requires very large exchange areas. Capillary tube mats make the necessary temperature level possible. Here, tubes 4 mm thin are spaced in narrowest intervals of 10 mm in the lower part of the solid ceiling. The tube surface therefore corresponds to the entire ceiling surface. The active surface is hereby more than twice as large as with conventional systems. Due to the small difference in temperature, the capillary tube mat works exclusively via radiation. This causes practically no thermal turbulences of the air and hereby an especially comfortable room climate. In the summer, the capillary tube mats are connected to a collector space in the soil.

This ground collector replaces a cooling machine. Thus, practically no energy expenses for cooling the building accrue. In the winter, a heat pump is switched to the ground collector. For the required heating, the principle of cooling is reversed and the soil is used as a heat accumulator. A heat pump heats the water to the required level of 30°C. The energy savings on conventional heating is around 75%. For its ecological energy concept, the object is sponsored within the scope of REN (economical use of energy and use of inexhaustible energy sources) of the federal state North Rhine-Westphalia / Germany.