The relative humidity of indoor air and its effect on people

Did you know that levels of relative humidity of indoor air have a direct or indirect impact on the health of building occupants? In the following article, we explain what this parameter is, why it is important to control it, and where the humidity inside our buildings comes from.

What is relative humidity?

Unlike absolute humidity, "the absolute amount of water vapor in the ambient air," relative humidity is "the mass of water vapor in the air per volume divided by the mass of water vapor per volume at saturation point at the same temperature."

Why is it important to control relative humidity?

The humidity in the air inside a room has a direct or indirect impact on people's health. Here are some of the consequences that arise from excess humidity:

• Affects thermal sensation (perceived temperature).
• Creates an ideal environment for the growth of fungi (such as mold) and house dust mites, which cause allergic ailments and unpleasant odors.
• Increases the emission of chemical products (formaldehyde, among others) from materials.

If, on the contrary, we find ourselves with low humidity:

• Feeling of dryness and irritation (both of the skin and mucous membranes) in some occupants.

To avoid health problems stemming from excessive or insufficient humidity, it is advisable to maintain relative humidity between 40% and 60% (never exceed 70%), in order to eliminate the risk of condensation (it should be noted that water in ventilation and air conditioning systems is the ideal medium for the proliferation of fungi and other microbiological agents).

Where does humidity in a building come from?

• From wet rooms: from kitchens due to cooking appliances, and from bathrooms due to the use of hot water. In these rooms hygro-regulable fans are recommended, as they adapt to levels of relative humidity.
• From human respiration of the occupants. Thus, a high level of activity in the rooms will result in high rates of pollutant production.Rate of water vapor production: -from a sleeping adult: 0.014 l/s -from an active adult: 0.019 l/sRate of CO2 production: -from an inactive adult: 0.004 l/s -from an adult doing light work: between 0.006 l/s and 0.013 l/s
• From domestic activity: -electric cooking: 2000 g/day -gas cooking: 3000 g/day -washing dishes: 400 g/day -personal hygiene (bath or shower): 200 g/day per occupant -Drying clothes indoors: 1500 g/day per occupant
• From the subsoil: depending on the type of construction, water vapor may enter through the ground floor of buildings (the pressure differences and the tightness of the ground floor will condition the rate of water vapor entry), so the designer should consider this aspect.