Dehumidifier prevents the growth of mould in Mästerby Church, Gotland
Mästerby Church is situated in western Gotland. Built from limestone in the 13th century, it has had problems in recent years with damp and mould. The problem arises when high external temperatures and humidity levels meet the cooler interior of the church. A dehumidifier has been installed in Mästerby Church to ensure humidity is kept at a reasonably constant level and to reduce the risk of mould developing.
Mästerby Church.
The mould problem at Mästerby Church, Gotland, was discovered when mould was seen growing on one of the inside walls in the church accompanied by its characteristic smell. Mould is caused by a particular combination of temperature and relative humidity. Relative humidity is the proportion of water vapour contained in the air at a certain temperature relative to the maximum amount of water vapour the air is able to contain at the same temperature. When warm air containing water vapour enters cool buildings, the air is cooled and the air temperature falls so that the water vapour condenses inside the building.
The solution
A dehumidifier has been placed at the back of the church and new procedures have been introduced for the church entrance. Even when there are a lot of visitors during the summer season, the door is kept closed to reduce the risk of warm air getting into the church. A dehumidifier cools the air and the water vapour in the air condenses into a container. The dehumidifier is controlled by the relative humidity in the church and switches on when the humidity level rises. After two years of measuring changes in air humidity and temperature it was noted that the dehumidifier and the new procedures had had the intended effect. Measurements, and the observations of members of staff and visitors, show that the environment inside the church has improved. The dehumidifier was introduced following discussion with all relevant parties, including the heritage authorities. It is switched off and moved when there are functions in the church so that it does not have an effect on how visitors experience the space visually and acoustically.
Financing
The dehumidifier cost SEK 6,000, which was paid for by the parish, and energy costs are around SEK 1,000-3,000 per year. The dehumidifier needs regular inspection and the water container has to be emptied as necessary.