The psychrometric chart and measurement of air humidity

Do you know what a psychrometric chart is? Do you know the relationship between relative humidity and comfort? In this article, we advance some concepts.

What is a psychrometric chart?

A psychrometric chart is a graphical representation that allows us to know the connection between the relative humidity of the air, the dry temperature, and the water vapor content per volume of dry air. It should be noted that water can be found in the atmosphere in three states: liquid, solid, and gas. Among them, the predominant state is the last one. The air, through which we can ventilate and condition our indoor environments, is made up of a combination of dry air and water vapor.

Psychrometric chart: a measurement tool

The science that studies the thermal characteristics of air, when it presents a certain level of humidity, is psychrometry. This discipline studies, similarly, its control, evaluation, and the consequences that this humid air has on the people inhabiting the spaces, as well as on all the elements that constitute that space, since humidity is a quality of the air that alters both its physical qualities (those of the air itself) and those of the people.

If we want to prevent health problems, maintaining relative humidity levels in the air within the recommended parameters (around 50%) is essential. There are devices in the market capable of measuring the relative humidity of the air: psychrometers. These devices have two thermometers: one with a dry bulb and another with a wet bulb. The first shows the air temperature; the second, since it undergoes a cooling process through water evaporation, shows a lower temperature than the first. Thanks to these two values, and the relationship between the enthalpy of the air (the proportion of energy exchanged with the environment) and that of a wet bulb, one can know the relative humidity of the air.

Efficient and healthy ventilation

As we mentioned earlier, it is crucial to control the relative humidity levels of inhabited spaces. A level above or below the recommended limits negatively influences the comfort, well-being, and health status of individuals. Thus, excessively humid air is a breeding ground for the proliferation of molds and dust mites. Conversely, excessively dry air causes dryness and irritation in mucous membranes.

The necessary ventilation of rooms to renew the air can lead to humidity problems if the ventilation system used is inadequate. Traditional ventilation (natural ventilation), in addition to proving inefficient (due to scheduling and energy efficiency concerns, windows cannot be opened as much as needed), does not meet the comfort and well-being needs. This is because when we ventilate this way, the incoming air from outside is untreated and unfiltered. Therefore, along with the air, we also incorporate particles (dust, soot...) and water vapor (since the air comes in with the hygrometric characteristics of the outside).

A good solution to ensure that the air supplied to our homes is adequate is the installation of a controlled mechanical ventilation double flow system. Thanks to this system, we can enjoy quality indoor air regardless of the relative humidity level of the outdoor air.