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Results

This construction project is ground-breaking, as no other office building of this size has as yet been built in accordance with the passive house concept. Integral planning was a prerequisite for the cost-effective and energy-efficient construction, which according to the building cost index is in the mid-range of the costs usual for conventional office buildings, despite a layout which is also sophisticated in the interior. Precise planning, prefabrication, and intensive quality control enabled a building envelope which is almost devoid of thermal bridges, and which is very air-tight – prerequisites for a well-functioning passive house. The quality of the furnishing and the thermal comfort aid the investor in the attempt to attract tenants. Also, in the tenancy agreement, an upper limit of €0.75/m² is guaranteed for the monthly ancillary costs incurred by heating, cooling and ventilation. However, at €12/m² per month, the rent is relatively high from a local perspective. Upon completion of the building at the end of 2002, there was a great deal of unoccupied office space in Ulm, so renting out was correspondingly difficult. In 2004, the proportion of rented floor area increased from an initial 31% to 60% at the end of the year. In 2006, it is 80%.

The Foundation is considering utilisation of the passive house standard again in a new construction project. The concrete core temperature control, with the borehole heat exchangers as heat sink and heat source, has proven a success for cooling and heating the building. The passive house standard offers very good prerequisites for this, as due to the low heat losses, the building element temperatures must only deviate very slightly from the target room temperature. Even overnight, the building does not cool down significantly, which makes a morning heating phase unnecessary. When cooling is required, the concrete core temperature control allows a load interruption of several hours each day, during which the cooling capacity of the borehole heat exchangers is used for cooling the supply air. The excess room heat which is temporarily stored in the building elements is then dissipated overnight. This saves having to use compression refrigeration machines or cold storage technology to cover the peak load.

For heating, cooling and auxiliary electricity with the current level of utilisation, the building requires only about 25% of the final energy required in a conventional office building. Nevertheless, with heating energy consumption of 34.6 kWh/m² p.a. in 2005, this is significantly higher than the calculated requirement and the passive house specifications. Missing here, most importantly, are the internal yields, which full occupancy of the building would entail. In order to pass final judgement on the success of the project, it is necessary to wait for data from years of full occupancy. Long-term monitoring over 5 further years will provide the data basis.

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Construction physics, BTE & simulation
ebök Planung und Entwicklung Gesellschaft mbH

Construction management
FREIE PLANUNGSGRUPPE 7