Why must ventilation systems always be on?

The image is so common that many of us find it normal and it is part of many routines. This image is as follows: we are in a room, it is hot, and we grab the remote control of the air conditioning unit. We turn on the device and, after a while, we are cold and we turn it off. If the climate is more pleasant afterward, we open the windows and let in the outside air. We have control over it, or we believe we do. But what about the ventilation systems that are always on? Can't we turn them off? Well, not in modern systems. While many people are unaware, even when acquiring a comprehensive ventilation system, that these solutions must always be running.

Although some users may find it strange, mechanical ventilation systems must always be on. They cannot be turned off for a while, as is done with air conditioning or even traditional heating systems. And, of course, they do not consume as much energy as some imagine.

Comprehensive ventilation solutions must be functioning constantly. Moreover, this is something that is implicit in the Technical Building Code, in the basic document HS 3 of indoor air quality. It clearly specifies that mechanical ventilation systems must be working at all times, although it is good that they adapt to the specific moment.

Why? For a more logical reason than it might seem. Nowadays, modern construction regulated by the same CTE has a great capacity for airtightness. The joinery and the other materials used make homes very difficult for outside air to penetrate. This protects us from pollution and, above all, it means that we suffer less from temperature changes inside the premises. In summer, it's less hot, and in winter, the cold is more bearable. We have very airtight homes that gain a lot in energy efficiency but require advanced ventilation solutions in return.

The problem with this powerful airtightness is that air does not pass through easily either. It is not enough to open windows occasionally, as the air must be renewed frequently and a flow must be maintained. Mechanical ventilation systems will facilitate air circulation in the rooms. Some details to keep in mind and highlight are:

• There is an obligation to install ventilation systems by the CTE, and they cannot be turned off. There are no on and off buttons; everything must work constantly.
• To perform more efficiently, it is ideal for the extraction flow to vary depending on the humidity in bathrooms and kitchens. The CTE also specifies these values.
• Mechanical ventilation systems always on consume much less than we think, especially if they are intelligent.

Always on ventilation systems but energy-saving

Many users fear that ventilation systems always on might be a waste on their electricity bill. But nothing could be further from the truth. In some cases, these ventilation units can have a similar or even lower consumption than many of the appliances we have at home.

While traditional air conditioning and heating units have always been high consumers, this is not the case for ventilation systems, as they are comprehensive solutions influenced by many other factors, such as how the house is constructed.

As we have mentioned, the CTE requires buildings to be constructed with great airtightness, isolating their inhabitants from cold and heat. This is already an advantage when considering utility expenses. From there, air renewal also plays a fundamental role in our comfort at home.

To avoid losing the energy we use, a heat recovery unit can be used. In these cases, part of the energy used is reused as it converts into power to climatize the room.

The best system for these cases is double flow mechanical ventilation with a heat recovery unit. In the specific case of passive houses with the Passivhaus standard, we find the perfect example of how heat recovery can help, through ventilation systems always on, to have a very modest expense on the electricity bill. In passive houses, energy recovery is achieved through aerothermal energy, and the only mechanical element in the construction of these houses is the ventilation system itself. This indicates that we can have contained expenses in utilities while still ensuring that ventilation does not stop running in our homes.