Relative humidity control

June 19, 2018

What instruments do we use to control humidity? What is the finality? What consequences can excess or lack of humidity have?

Humidity

The concept of humidity or amount of water vapor present in the air is very complex, since it depends on many factors such as temperature and pressure. To facilitate reading, several concepts have been defined:

Air humidity: Amount of water vapor that is present in the atmosphere.
Dew point : Temperature at which water vapor begins to condense on surfaces. Without changing the content of water vapor present in the air.
Specific humidity: Amount of water vapor in (gr) contained in 1kg of humid air.
Mixing ratio or mixing ratio: Amount of water vapor (in gr) contained in 1kg of dry air.
Relative humidity: relative humidity is defined as the percentage (%) of vapor pressure that the air has with respect to the maximum that it can have at that temperature. It is the most common way of measuring humidity.

Being clear that we will use the concept of relative humidity, we will define 3 ranges:

High: between 70 and 100% (saturation)
Average: between 40 and 70%
Low: between 0 and 40%

Related product: Barigo hygrometer

Measurement instruments

The instrument par excellence that measures relative humidity is the hygrometer. From hygrometers we can find different models according to the mechanism or operating system.

We divide them into two main major groups:

Analogue
Digital

The analog hygrometers work without any battery, and can have an internal system of bimetal spiral or of hair, whether synthetic or natural. Both systems are hygroscopic or sensitive to changes in humidity, experiencing length variation that is transmitted in the movement of the needle.
Digital hygrometers incorporate a so-called capacitive probe, with an internal material, also hygroscopic in nature. The change of the state of the internal material is translated into an electrical signal or impulse and from here to a digital system until the LCD screen indicates the exact humidity value.
There are other instruments for humidity measurement, in this case indirectly. This is the psychrometer and is based on the concept of temperature or dew point. It consists of two thermometers, one dry and the other connected to a tank with (wet) water. The wet thermometer marks the temperature or dew point, and by deference between the two temperatures and a base table, we can determine the% of relative humidity

Moisture assessment

Humidity is a very important and transversal control parameter in different areas. In meteorology, construction, environmental control, heritage conservation, museum, health, food, etc ...

In meteorology it is a parameter present in most meteorological stations, humidity is related to the presence of water vapor in the troposphere and therefore with the presence or absence of clouds, mists, dew, precipitation etc ...

In construction and housing, the presence of high humidity is a big problem, it can indicate from poor ventilation to the presence of leaks, humidity, subsoil humidity, etc. and therefore induce the presence of fungi and / or mold

In heritage and museum, humidity control is essential for a good preservation of works of art and documents, the presence of excessive humidity can damage documents and works of art of great value.

In health, excess humidity or lack can cause certain respiratory problems in children and adults, or accentuate certain diseases such as asthma or lung failure. Humidity control inside homes and rooms is basic in these cases.