Under the management of the Saxon State Office for Construction and Real Estate Management (Sächsisches Immobilien- und Baumanagement, SIB), the individual buildings of the estate, originating from different historical periods, are being comprehensively refurbished in phases through the end of 2026.

The site of the Saxon Competence Centre for Sustainable Agriculture, Fisheries and Climate in the Lusatian Region comprises a listed historic ensemble consisting of an 18th-century castle, a former fodder barn, an orangery, and a residential building for trainee inland fisheries specialists. In addition to adapting the floor plans to meet the current needs of the users, the refurbishment must comply with statutory requirements while, above all, preserving the architectural and historical value of the listed buildings in accordance with heritage conservation principles.

Picture 1, 2: Castle building (south façade with lecture hall on the upper floor); existing timber beam ceiling in the future air handling unit (AHU) plant room in the attic prior to refurbishment.

Despite the specific requirements associated with the historic building, the project is intended to serve as a showcase for the use of renewable energy technologies at the Saxon State Office for Environment, Agriculture and Geology (LfULG). In addition to a photovoltaic system designed to supply a significant share of the site's electricity demand, a ground-source heat pump has been installed to provide the base load for the heating system.

The project is also part of the German Investment Act for Coal Regions (Investitionsgesetz Kohleregionen – InvKG). It is fully funded through the Structural Development Fund for the Saxon Lignite Mining Region and co-financed with tax revenues from the budget of the Free State of Saxony.

Following a competitive tendering process, the Bautzen branch of the Saxon State Office for Construction and Real Estate Management (Sächsisches Immobilien- und Baumanagement, SIB) commissioned ILK Dresden with the redesign of the building's plumbing, heating, ventilation, air-conditioning (HVAC), building automation systems, and geothermal energy system. During the extensive refurbishment works and the installation of an air-conditioning system in the historic attic of the castle, one of the greatest challenges was preserving one of Saxony's maternity roosts of the serotine bat (Eptesicus serotinus). This colony is among the largest of its kind in the state.

Picture 3: Drilling of a geothermal borehole, installation of a double U-tube ground heat exchanger, pressure testing, and borehole grouting.

Picture 4: Two new air handling units (AHUs) are being precisely installed within the restored roof structure during the period when the bats are absent from their maternity roost.

As no established standards exist regarding the acoustic environment required for such bat roosts, ILK Dresden was commissioned to conduct acoustic measurements of the existing ventilation systems before refurbishment. These measurements documented the baseline sound conditions and established reference values that must not be exceeded by the new systems. After completion of the construction works and commissioning of the new HVAC systems, follow-up measurements will be carried out to verify compliance with these sound pressure level limits. This scientifically based measurement approach ensures that the modernisation of the building services can be achieved without compromising the habitat of this protected bat colony, demonstrating how engineering expertise, heritage conservation and species protection can be successfully integrated within a single refurbishment project. Another challenge is that work on the roof and within the attic space may only be carried out outside the bats' maternity roosting season, i.e. between approximately September and April. However, bats do not follow the Gregorian calendar when moving into and out of their summer roosts. As a result, construction scheduling requires a high degree of flexibility from all project partners to accommodate the animals' natural behaviour.

After the refurbishment, the castle's former ballroom will continue to be used as a lecture hall, training facility, and conference venue. To improve thermal comfort, the room will be equipped for the first time with an indoor air-conditioning system that supplies conditioned air through air-permeable acoustic wall panels. Since no standardised design methods exist for this type of displacement air outlet, ILK Dresden was commissioned to assess the ventilation concept. The investigations included the design of the rear air supply, the airflow distribution within the displacement ventilation wall to ensure a homogeneous, low-velocity air supply, and the evaluation of the acoustic performance of different prototype elements for cooling operation.

Pictures 5, 6, 7: Open rear side of an air-permeable acoustic wall panel, Pressure loss measurement on a test chamber test rig, Laser-based airflow visualisation

The pressure loss characteristics of the wall elements were determined using a test chamber facility. The airflow investigations were carried out in a thermally neutral test hall, where the flow patterns were visualised using laser-based measurement techniques.

As a result, ILK Dresden has further expanded its engineering portfolio by offering additional value-added services to its clients. All relevant measurement, simulation, and design services for building services engineering can now be provided in-house – from initial feasibility studies and concept development through detailed design and commissioning support to warranty monitoring.

The Saxon State Office for Construction and Real Estate Management (SIB) regularly informs its employees and the public about its most significant construction projects through its corporate magazine. In the current issue (01/2026), the project managers responsible for the Königswartha Castle refurbishment emphasise that a project of this complexity—including the protection of 225 serotine bats - can only be successfully delivered through fair, collaborative, and constructive cooperation among all stakeholders. Their conclusion aptly summarises the challenge: "Conducting the entire orchestra."