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Ventilation unit at the Karlstejn castle

The purpose of the project was to design, manufacture and install a ventilation unit which will maintain the desired level of humidity and temperature in the Chapel of the Holy Cross at the state castle of Karlstejn. The control system of the unit constitutes a component of the whole control system of the Chapel’s parameters with a super ordinate operative division located in the Burgrave’s Palace.

The Chapel of the Holy Cross and the Karstejn castle

The Chapel of the Holy Cross is a space with arched walls panelled with gold foils and semiprecious stones. On the walls of the Chapel, there were 229 wooden paintings by Master Theodor. The windows and arched ceiling of the Chapel had not been insulated. The walls of the Chapels, which can be as thick as 6 m in some areas, developed a large amount of cracks.


  • Plastering full of cracks and holes,
  • Goldfoils pealing and semiprecious stones falling off,
  • Bended wooden paintings.


The parameters of the inner microclimate (warmth and humidity) do not in the least suit to the surfaces, arched ceilings and paintings. The initial ventilation by opening windows failed (paintings continued to bend). Eventually, the Master Theodor paintings were removed and deposited elsewhere. Hermetisation of the area also failed (to resolve the issue of mould coating the walls). In respect to the unkept inner area and lasting issues, the National Gallery suggested the paintings be placed elsewhere (August 1999).

Therefore it has been decided that the base for the subsequent solution be the adjustment of the inner microclimate of the Chapel. The works on the air-conditioning project had begun. The documentation with the details of two-year monitoring and data gathering conducted by the university department of electrical studies was made available to the designers. After the consultations with specialists, the entries for air-conditioning systems were prepared.

The desired parameters were as follows:

  • Temperature: 10 to 14°C
  • Relative humidity: 45 to 50 %.

To meet this requirement, the arched ceiling had to be insulated (orsil of 160 mm thick, sealing off the windows).

In regards to technical equipment, a PZP ventilation unit was installed in the side area beside the Chapel also called ‘babinec’ (women party).

The unit is equipped with a programmable computer. The computer receives impulses from sensors placed on the walls and under the paintings.

The size of the unit is atypical mainly due to the requirements related to the transportation and installation into the given space.

  • Minimal exhale speed.
  • Minimal noise level.
  • Continuous air flow in the Chapel of the Holy Cross.


Other requirements

The conductors of the sensors must be designed in a way so that they cannot be seen on the wall (of the same colour as the wall). The area with the air-conditioning unit and the area of the Chapel are in fact two individual fire divisions. Therefore a fire damper has to be fitted at the border in the air-conditioning pipeline.

Considering the fact that the walls of the Chapel are rather massive, the response to the outdoor temperature and humidity change is expected to be very slow. Everything will thus depend on the operation of the air-conditioning unit.

Another important aspect is the adjustment of the visiting hours. Lesser amount of people will be allowed in the Chapel where they will be able to spend shorter period of time.

Evaluation of the whole project

The air-conditioning system has been up and running for the past 10 years. During this time, there has not been any further damage to the plastering, surfaces, paintings or furniture.

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