Overview

Office environments that are air conditioned during the summer and heated in the winter will suffer from low humidity without correct humidification. Prolonged exposure to a dry atmosphere will effect the health of staff, increase absenteeism and lower productivity.

One of the first noticeable effects of dry air is electrostatic shocks, which occur below a threshold of 40%RH. Other less recognizable effects include dry itchy skin, contact lenses prematurely drying out and causing discomfort, sore eyes and throat, and an increase in dehydration.

Tests have shown that the transmission of airborne viruses, such as influenza, are greater at a low humidity. Maintaining an optimum humidity will reduce airborne transmissions on an office and reduce absenteeism.

The recommended level of humidity for human health is between 40-60%RH. To maintain this level large offices will employ industrial humidification systems within the central air conditioning system. However, in-room humidifier systems are available that can introduce moisture directly and discretely to a room's atmosphere.

Health

Correct humidity levels are essential to health. Deviations from the mid-range of relative humidity (RH) of 40-60% can reduce air quality by causing an increased growth of bacteria, viruses, fungi and mites. Bacteria and viruses, in particular, thrive in an environment where the air is too dry. Studies have shown that when the indoor RH drops below 40 percent, absenteeism due to illness increases. Conversely, if the air is too moist (above 60%), allergies and asthma increase due to the growth of fungi and mites.

Comfort

Correctly humidified rooms feel warmer and more comfortable, especially in colder climates where heating systems are required.

The Sterling Chart – optimum RH for health

The Sterling Chart below illustrates how RH affects health and well being. Colds, flu, sore throat, dry eyes, itchy and cracked skin are all symptoms that are usually prevalent in the cold dry months of the winter when the indoor RH is at its lowest. The increase in bacteria, viruses and ozone production (caused by static electricity) in low RH levels all have an adverse affect on health.

How does the outdoor temperature affect the indoor humidity level?

Admitting cold outdoor air into a space will lower the indoor RH. When the lower temperature outdoor air is brought indoors and heated, it loses moisture and reduces the overall RH.

For example: if the outdoor temperature is 0°F and 50% RH and the air comes indoors and is heated to 70°F, the residual moisture after heating the outdoor air will only be about 3% RH. Even on a nice, sunny 35°F and 50% RH day, the residual indoor RH will only be about 14%.