Natural cross ventilation, pros and cons

There are many ways to ventilate a house, but how many of them are efficient? Traditionally, it was thought that simply opening the windows and letting in air from outside was sufficient, but modern construction and the new regulations of the Technical Building Code have highlighted the necessary renewal of air indoors, both for health and comfort reasons. And in the event that there are no mechanical ventilation systems, a good option is to achieve natural cross ventilation in the home.

Achieving air renewal indoors through natural cross ventilation is something that can be considered before starting construction, but it is also possible to implement it in almost any home, especially in houses, since it can be more complicated in apartments. It's inexpensive and in many cases effective. How can we define natural cross ventilation? We could say that it involves two openings in the same space or room being located on opposite or adjacent walls, which will allow for the easy entry and exit of air. Obviously, this type of ventilation solution is ideal for places with high temperatures, since the main benefits of natural cross ventilation are two:

1. Great air renewal. Although there are no automatic mechanisms that read the specific needs of a space in real time and act accordingly, the reality is that with this type of natural ventilation solution, air entry and exit are achieved. For this reason, renewal is greatly accomplished.
2. Improvement of thermal comfort in warm climates. The fan effect means that people in the same room notice the climate much more pleasantly. If the wind is in constant motion, they will undoubtedly feel a better thermal sensation. Likewise, by changing the air that has absorbed heat indoors, temperatures should drop.

The effect of natural cross ventilation is possible thanks to the opposite positions of the two openings in the same room. In an apartment it may be more difficult to achieve, but it can sometimes be done by opening the window of a living room and opening the door if it leads to another airflow. In those cases, we can find different ways to achieve good airflow.

In a house, it is undoubtedly much easier to achieve this type of natural ventilation as you can find doors leading to the outside near windows that lead to other areas. Is this effect always equally efficient? Not at all. There are several concepts to consider to maximize the effectiveness of cross ventilation naturally. For example, the following should be taken into account:

• The warmest air currents come from the south facade of houses.
• As air rises in temperature, it rises upwards.

In this way, if we want to plan a construction that takes advantage of natural cross ventilation, it is important to place doors and windows on the south facade, as that is where we will want to extract the warm air from indoors. From that point, we can choose to install fans that send air outside the home through these openings.

Similarly, the windows from where we want the outdoor air to enter must be positioned to the north of the home. And just by having implemented these solutions, we will have undoubtedly gained a lot in terms of the ventilation of our home without relying on mechanical or traditional air conditioning systems.

Hybrid systems, support for natural cross ventilation

As we have said, while we can implement a natural cross ventilation system in almost any home, it is better to plan it beforehand in a construction to face openings in the most comfortable way possible. Nevertheless, the Technical Building Code, in its Basic Document HS3 specifies that it is necessary for homes to have at least one hybrid ventilation system.

To combine with cross ventilation, it is a good alternative to install a controlled hybrid ventilation system (VHC), which is characterized by activating mechanical ventilation when natural ventilation is insufficient. In this type of mechanical systems, the air entry occurs naturally through ventilation grills that introduce air from the outside. The extraction can be done naturally or mechanically.

In any case, the solution of natural cross ventilation will always be something to consider if we have to rely on natural air renewal systems. But it is important to keep in mind how mechanical ventilation systems work to ensure a proper airflow in our homes, as well as in workplaces.