August 19, 2019

Factors that affect the control of the humidity and its level


What influence the level of humidity?

Humidity goes up and down because it is affected by different factors around us, like the temperature and our actions (e.g. opening a door).

Let’s look at 3 factors which highly influence the control of the humidity and its level:

the temperature, the HVAC system and the building itself.


As mentioned in a previous article, “Relative humidity VS. Absolute humidity“, the amount of moisture that can be included in a room varies with its temperature level. Thus, temperature is also highly related to humidity.

As the temperature rises, the amount of moisture that can be included in the air also increases. Therefore, the relative humidity changes even if the absolute humidity is the same.

To illustrate this theory, let’s continue the example used in the previous article.

In a room (representing the air), there is a fixed number of seats. The moisture is represented as a person (1 water droplet = 1 person). And we will assuming that one person is 0.001 kg.

  • When the temperature is 16.5°C, there are 12 seats and 6 people sit.
    • The absolute humidity is 0.006 kg/kg’ and the relative humidity is 50%.


  • When the temperature reaches 25°C, the number of seats increases to 18 seats. There are 18 seats now and still only 6 people sit.
    • So the absolute humidity is the same as before, 0.006 kg/kg’. However, as the overall number of seats increases and the degree of congestion changes, the relative humidity will be about 30%.

That is why it feels dry in winter even when the humidity of the outside air is 50% because the amount of water present in the air is small.

HVAC system


Ventilation and Air conditioning are intended to maintain indoor comfort by eliminating hot and humid air and renewing the inside air with fresh outside air.

Insufficient ventilation will cause mold and condensation if the humidity rises too much.

In addition, the amount of ventilation required to discharge indoor carbon dioxide and chemical substances and keep the air in the room clean is referred to as the required amount of ventilation.

For example, the amount of ventilation required for an office is 6.0m3/h per 1m2

There are 2 methods of ventilation:

  • Natural ventilation: it is performed by opening and closing the windows and clearances provided at the entrance and exit.
  • Mechanical ventilation: it is a system installed with an air inlet and an outlet. It forcibly takes in outside air using a fan and simultaneously discharges it.


Therefore, the amount of ventilation and air conditioning changes greatly depending on the temperature, the natural air flow (wind), and the occupancy density of the room.

The humidity of the room will also change with the air coming from the outside as it alters the temperature level at the same time.


The air tightness of the building and the building materials also greatly affect the humidity.

  • Air tightness

By making the air tighter, you can minimize the effects of outside air, so you can use temperature control and ventilation systems to control temperature and humidity. Even with air conditioning, energy saving and comfortable air conditioning can be performed, leading to the saving of energy costs.

  • Building materials

In recent years, reinforced concrete and new building materials are often used, and it has become difficult to control condensation with humidity control. Therefore, development of new construction materials with humidity control function such as diatomaceous earth and wood-based cellulose fiber has increased.

Using materials that absorb water vapor generated in the building and release the moisture when the room is dry helps to control the humidity naturally.

To summarize, if you optimize these 3 factors in your building / factory, you will be able to control the level of humidity and increase the relative humidity needed for your process.

Stay tuned for the next article about humidification!