Poul Klenz Larsen
The climate control in Danish churches is a compromise between the demand for human comfort and the need for preservation. Most medieval churches are heated in winter and left unheated in summer. The consequence of this heating practice is large variations in the relative humidity. To control the relative humidity within reasonable limits, the churches should be heated all year, and the temperature should be adjusted to an annual cycle. A moderate relative humidity can also be achieved by mechanical dehumidification, but the effect will sometimes be spoiled by evaporation of water vapour from an internal source. Some churches have the ability to humidify the indoor climate by capillary migration of moisture through the structure. Such processes must be accounted for when devising the heating strategy for a particular church. Further investigation is needed to locate the source of the passive humidification. The conflicting interests of congregation and conservation can sometimes be solved with transparent walls or glass doors to define specific climate zones with independent climate control.