Hygro-regulable and auto-regulable air in mechanical ventilation

In the solutions for mechanical ventilation, many factors must be evaluated in their installation and planning to maximize air renewal possibilities. Among them are the air inlets, which will allow air to pass into rooms through ducts. We can find different types of hygro-regulable air inlets and auto-regulable ones, among others, that will allow enjoying outside air in rooms such as bedrooms and living rooms, among others. The differences will relate to how they will modify the volume of air to be introduced.

In modern buildings, high airtightness and thermal insulation have allowed rooms to experience fewer problems with poor air conditioning, making it easier to maintain warmth in winter without the need to spend on air conditioning. However, by sealing air leaks through walls or doors, we find that we need mechanical ventilation solutions to introduce the necessary air.

This is stated in the Technical Building Code, in the Basic Document HS3, which requires at least having a hybrid ventilation system that uses mechanical systems when natural ventilation doesn’t reach the necessary minimum.

Mechanical ventilation considers that, in homes and workplaces, the extraction of air that has lost quality— for example, due to excess humidity or contamination from cooking or chemical use— will be carried out from wet areas: mostly bathrooms and kitchens. The air inlets, conversely, will be located in dry areas, such as living rooms and bedrooms.

The air inlets must be placed at least 1.80 meters above the floor, as otherwise, they may disturb the residents from the airflow. It’s important to consider that warm air usually accumulates in the upper areas of rooms, while cold air tends to descend to the ground. This is significant regarding temperature differences in winter and summer.

Differences between hygro-regulable, fixed, and regulable air inlets

These air inlets—also known as air ventilators— can be of different types, although we can predominantly find the following models:

• Fixed air inlets. They simply allow the passage of air from the outside to the rooms. In this case, regulation is absent, and the air entry will depend more on the other factors of the ventilation installation.
• Auto-regulable air inlets. Here, the entry of air will adapt to the real needs of the ventilation flow to maintain its constancy. They have interior parts that allow for modulation of abrupt air changes, preventing unexpected effects, such as drafts in the house or over-ventilation.
• Hygro-regulable air inlets. This type of ventilator focuses on the humidity factors of each place. In this case, they will always operate based on the water vapor values in the air. When the relative humidity is quite high, the inner flaps will open the passage of air widely to eliminate humidity. When the humidity is lower, the flaps will close to minimize the airflow, thus avoiding higher energy consumption.

In the case of hygro-regulable air inlets, it's important to note that their function is not only to introduce renewed external air, but the distribution of ventilators and ducts should be carried out and planned based on the relative humidity ratio in the home, in addition to the ventilation needs of dry rooms.

That’s why the airflow is not distributed the same at all times since it considers the number of occupants in each room of the house and also the exact situations at each moment. The airflow in the hygro-regulable air inlets varies between 6 and 45 m3/h, depending on the real humidity needs at any time.

The decision to install mechanical ventilation systems with fixed, auto-regulable, or hygro-regulable air inlets will depend on many factors to consider. Fixed systems are for those places with lower ventilation needs and homogeneous conditions, while auto-regulable ones are ideal when the main need is to ensure a ventilation flow. In the case of hygro-regulable air inlets, we can use them— or combine them with others— in cases where we need to control the indoor relative humidity and eliminate excess water vapor in the air.