Wednesday, June 14, 2006

Site: Kassel - Building Research Institute

Improving the indoor climate

In moderate and cold climates people usually spend about ninety per cent of their time in closed buildings. So the indoor climate is very important for their well-being. Their comfort depends on room air temperature, air movement, air humidity, radiation to and from surrounding objects, and the pollution of the air.
If the temperature is too high or too low, it is realised at once by the inhabitants, but the negative influence of too high or too low humidity is not common knowledge. The air humidity inside rooms exerts a significant influence on the health of the inhabitants, and earth has the ability to balancing indoor air humidity like no other building material. This recently investigated fact is described in detail later in this section.

Air humidity and health
From the research done by Grandjean (1972) and Becker (1986) we know that a relative humidity of less than 40% over a long period may dry out the mucous membrane (slime film) which can lead to decreased resistance to colds and related diseases. This is because normally the mucous membrane of the epithelial tissue within the trachea absorbs dust, bacteria, viruses etcetera and returns them to the mouth by the wavelike movement of the epithelial hair. If this absorption and transportation system is disturbed by drying out, these foreign bodies reach the lungs and may cause health problems. (See fig.)
A high relative humidity of up to 70% has many positive influences: it reduces the fine dust content of the air, activates the protection mechanisms of the skin against microbes, reduces the life of many bacteria and viruses, and reduces odour and static change on the surfaces of objects in the room.
A relative humidity of more than 70% normally feels unpleasant probably because of a reduction in the oxygen intake of the blood in warm-humid conditions. Increasing rheumatic pains are observed in cold humid air. Fungus formation increases significantly in closed rooms when the humidity rises above 70% or 80%. Fungus spores in large quantities can lead to various kinds of pain and allergies. From these considerations, it follows that the humidity content in a room should be a minimum of 40% and not more than 70%.


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