The right level of humidity makes a vital contribution towards various situations in daily life – in a business environment as well as in your private home. The moisture content of the air is so important that in many countries there are clear guidelines for the operation and maintenance of humidification systems.
A narrowly defined range of 40 to 60% relative humidity has been scientifically proven to provide ideal conditions for health, performance, well-being and value retention. In modern buildings with an impermeable building shell, central heating and ventilation systems, these limits cannot be met in everyday life without active humidification. This brochure is intended to outline the medical principles for the correct air humidity as well as the positive health and economic effects that can be achieved through correct air humidification in workplaces.
The pale blue field in the h,x diagram shows the optimum range for health protection. This range is based on the recommendations of numerous medical studies (direct link) which have investigated the relationships between the spread of germ droplets, the viability of viruses, the risk of infection and air humidity. Technical standards and specialist planners base their planning and operation of air-conditioning systems on this range.
h,x diagram according to Mollier to illustrate thermodynamic processes
Everyone knows the unpleasant effects of excessively dry air: The skin becomes flaky and cracked, and the mucous membranes of the nose and throat, as well as the eyes dry out and become irritated. This makes us feel uncomfortable and more susceptible to respiratory illnesses. But what are the reasons why room air is so unpleasantly dry, especially in the colder seasons?
A short digression into physics and thermodynamics provides answers.
Depending on the temperature, the air has a different capacity to absorb water. In winter, the cold outdoor air has only a low capacity to absorb moisture. By heating it (which increases the capacity to absorb moisture), the relative humidity is reduced further and a very dry room climate is created. Without active humidification, a healthy room air humidity of 40 to 60% is barely feasible.
According to a new study by Yale University, low air humidity considerably promotes and increases the spread of flu viruses (influenza) and thus the risk of infection and an often severe or even fatal disease.
In addition, in its reports on the epidemiology of influenza, the Robert Koch Institute (RKI) records cases of illness and death caused by influenza in Germany, showing a connection to the cold (dry) winter periods. In the report for 2017/2018, the Institute came to the following conclusions (see diagram: Number of acute respiratory infections):
Current findings of a study by the renowned Yale University
The graph shows a significant correlation between flu cases and low humidity levels from December to April.
Whether this correlation actually exists has also been a controversial topic of discussion in medicine. Proof has now been provided in May 2019 by researchers from the renowned American Yale University in their study “Low ambient humidity impairs barrier function and innate resistance against influenza infection”, which was conducted over many years. Without going too deeply into the medical details of this study on the influence of low humidity on the spread of influenza viruses and the resistance of humans to influenza viruses, key findings and results obtained by the researchers are as follows: