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Session Overview
WS8: Swegon workshop: Low relative humidity in indoor air – an important element of indoor air quality
Monday, 13/June/2022:
1:30pm - 3:00pm

Session Chair: Pawel Wargocki
Location: SN202

Session Abstract


In the recent years, indoor air quality research has been focused on air pollutants including VOCs and other species, Radon, particles, and dust etc. The aim was to define permissible levels of these pollutants to avoid the risks to comfort, health and other outcomes such as productivity and learning. Such information is important to equip buildings with technological solutions. There was less discussion on relative humidity and its importance as a modifier of the responses as well in the context of direct effects.

Relative humidity is usually discussed in the context of the thermal comfort criteria as well as perceived air quality because enthalpy of air modifies the perception of air quality. However, relative humidity seems to play much more important role in the context of IAQ and should be discussed on its own and consequently the methods allowing its control in the buildings.

The negative effects of high humidity (>70-80%) are well documented but these levels are rare and unusual. It is important to focus on low end and levels below 20-30% which are prevalent in a large population´s occupying buildings, especially during cold winters and when the continuous ventilation with outdoor air is in place. Few studies looked at these levels, some documenting potential negative effects

There is also a need to look at the effects of low RH for vulnerable populations as most of the work (if not all) is done with healthy people. What about the elderly and otherwise weak people? The discussion should also be potential adaptation to low RH.

Finally, the transmission of pathogens should be discussed in connection with low relative humidity especially that flu and common cold occur usually during winters with low RH indoors.


This workshop wants to initiate debate on the importance of low RH and which levels should create actionable decisions. We need more scientific studies of negative impact of dry indoor air in wellbeing and health.

One other reason for this debate is that the modern humidity recovery equipment in ventilation systems, control strategies and many humidity sources (mechanical and natural), gives new opportunities to minimize the energy costs and avoiding risks to have too high humidity levels in the buildings. Humidity control and humidity optimization is not so expensive as assumed if it is done.

Dry indoor air is a health and wellbeing problem, which is not so rare as expected

In Helsinki region one can find out that in winter months Nov 2018 -March 2019 roughly 2/3 or the working hours the indoor air humidity war lower than 20% RH. This can be considered extreme dry indoor air.

The workshop wants to activate the scientific community to study impact of the dry indoor air to different building user groups (children, elderly, students etc.).


Field measurements in Finland and Sweden

Timo Schreck Swegon AB

Health and wellbeing Impact of dry indoor air

Pawel Wargocki DTU

Need to study impact of extreme dry < RH 20-25% on health and wellbeing

Mikael Börjesson Swegon AB

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ID: 1853
Topics: 1b. Indoor air quality, health and wellbeing - Psychology of IAQ perception
Keywords: Humidity

Swegon workshop: Low relative humidity in indoor air – an important element of indoor air quality

Chair(s): Pawel Wargocki (DTU)

Presenter(s): Pawel Wargocki (DTU), Timo Schreck (Swegon), Mikael Börjesson (Swegon)

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