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Have we gone too far in avoiding humidity?

Mikael Börjesson


Humidity can have a positive impact on our health but is still often ignored when designing indoor environments. Too dry air can cause dry throats, chapped lips and facilitates the spread of viruses. Is it time to re-evaluate the cost for the society of having buildings with too dry indoor air?

There are clear legislative requirements on C02-levels and thermal comfort in most of the developed world. But there is a third dimension, relative humidity (RH), which is often forgotten. Is it because humidity is less important? On the contrary, many researchers claims that it matters a great deal.

Humidity levels need to be controlled

If the relative humidity level is too low, we get dry eyes and skin, chapped lips and some research even indicate that virus spread is worsened as humidity levels drop.  On the other hand, indoor environments with too high humidity levels result in growth of microorganisms that cause other illnesses, and may cause mold problems which are not just harmful to the house itself, but to its inhabitants. In other words, we need to control the humidity levels, so they are not too low, and not too high.

Problems with too dry air in northern Europe

In countries with more temperate and wet climates, the problem will naturally be that the humidity levels are seasonally too high. But too low levels is also a problem. Measurements show that in the cold and dry winters of northern Europe, indoor RH-levels can drop to 5-15% for extended periods of time. This is especially clear in offices and other working places which are lacking natural sources of humidity.

There are a few exceptions, In Poland a minimum of 40 % RH is required in indoor air humidity in working places. It is one of the few European countries where humidity is controlled systematically, at least in system design and execution phase.

Why are we ignoring humidity?

We have known for a long time that humidity can have a positive impact on our health. Humidified air and water vapor inhalation has been a popular self-care treatment and used also in hospitals for quite some time for respiratory illnesses.  So the question is why this knowledge is ignored when design indoor environments?

Our strive to avoid sick building syndrome, especially in the Nordic countries, has given humidity a negative ring to it. To avoid sick building syndrome and molds, high ventilation rates have been recommended, but there have been no requirements for humidity levels to act as a counterbalance, resulting in extremely dry indoor environments.

Humidity can be an asset

We use heat recovery in ventilation systems to save thermal energy. Besides that, control systems automatically start and stop the recovery based on whether we want to keep the thermal energy inside the building or remove it. What would happen to our indoor comfort if we treated humidity like an asset and recovered it and treated it in the same way as we do with thermal energy?

It is time to re-evaluate humidity

Too dry air is bad for our health and is a problem we need to put more attention to in order to create healthy indoor environments for all. We need to look at the actual cost of too dry air, in terms of sick leave rates, not to mention the human cost of poor health. Is now not the right time to see if we by controlling and treating humidity as an asset can create healthier indoor environments in buildings?